IETF MANET Working Group               David B. Johnson, Rice University
INTERNET-DRAFT                              David A. Maltz, AON Networks
2 March
21 November 2001                            Yih-Chun Hu, Rice University
                         Jorjeta G. Jetcheva, Carnegie Mellon University

                  The Dynamic Source Routing Protocol
                    for Mobile Ad Hoc Networks

                     <draft-ietf-manet-dsr-05.txt> (DSR)

                     <draft-ietf-manet-dsr-06.txt>

Status of This Memo

   This document is an Internet-Draft and is in full conformance with subject to all provisions
   of Section 10 of RFC 2026 except that the right to
   produce derivative works is not granted. 2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft is a submission to the IETF Mobile Ad Hoc
   Networks (MANET) Working Group.  Comments on this draft may be sent
   to the Working Group at manet@itd.nrl.navy.mil, or may be sent
   directly to the authors.

Abstract

   The Dynamic Source Routing protocol (DSR) is a simple and efficient
   routing protocol designed specifically for use in multi-hop wireless
   ad hoc networks of mobile nodes.  DSR allows the network to be
   completely self-organizing and self-configuring, without the need
   for any existing network infrastructure or administration.  The
   protocol is composed of the two main mechanisms of "Route Discovery"
   and "Route Maintenance", which work together to allow nodes to
   discover and maintain source routes to arbitrary destinations in the
   ad hoc network.  The use of source routing allows packet routing
   to be trivially loop-free, avoids the need for up-to-date routing
   information in the intermediate nodes through which packets are
   forwarded, and allows nodes forwarding or overhearing packets to
   cache the routing information in them for their own future use.  All
   aspects of the protocol operate entirely on-demand, allowing the
   routing packet overhead of DSR to scale automatically to only that
   needed to react to changes in the routes currently in use.  This
   document specifies the operation of the DSR protocol for routing
   unicast IP IPv4 packets in multi-hop wireless ad hoc networks.

                                Contents

Status of This Memo                                                    i

Abstract                                                              ii

 1. Introduction                                                       1

 2. Assumptions                                                        3

 3. DSR Protocol Overview                                              5

     3.1. Basic DSR Route Discovery . . . . . . . . . . . . . . . .    5
     3.2. Basic DSR Route Maintenance . . . . . . . . . . . . . . .    7
     3.3. Additional Route Discovery Features . . . . . . . . . . .    8    9
           3.3.1. Caching Overheard Routing Information . . . . . .    8    9
           3.3.2. Replying to Route Requests using Cached Routes  .    9   10
           3.3.3. Preventing Route Reply Storms . . . . . . . . . .   10   11
           3.3.4. Route Request Hop Limits  . . . . . . . . . . . .   12   13
     3.4. Additional Route Maintenance Features . . . . . . . . . .   13   14
           3.4.1. Packet Salvaging  . . . . . . . . . . . . . . . .   13   14
           3.4.2. Queued Packets Destined over a Broken Link  . . .   14
           3.4.3. Automatic Route Shortening  . . . . . . . . . . .   13
           3.4.3.   15
           3.4.4. Increased Spreading of Route Error Messages . . .   14   16

 4. Conceptual Data Structures                                        15                                        17

     4.1. Route Cache . . . . . . . . . . . . . . . . . . . . . . .   15   17
     4.2. Route Request Table Send Buffer . . . . . . . . . . . . . . . . . . .   17
     4.3. Send Buffer . . . .   20
     4.3. Route Request Table . . . . . . . . . . . . . . . . . . .   18   21
     4.4. Retransmission Buffer Gratuitous Route Reply Table  . . . . . . . . . . . . . .   22
     4.5. Network Interface Queue and Retransmission Buffer . . . .   19   23

 5. DSR Header Format                                                 20                                                 25

     5.1. Fixed Portion of DSR Header . . . . . . . . . . . . . . .   21   26
     5.2. Route Request Option  . . . . . . . . . . . . . . . . . .   23   28
     5.3. Route Reply Option  . . . . . . . . . . . . . . . . . . .   25   30
     5.4. Route Error Option  . . . . . . . . . . . . . . . . . . .   27   32
     5.5. Acknowledgment Request Option . . . . . . . . . . . . . .   29   35
     5.6. Acknowledgment Option . . . . . . . . . . . . . . . . . .   30   36
     5.7. DSR Source Route Option . . . . . . . . . . . . . . . . . . .   31   37
     5.8. Pad1 Option . . . . . . . . . . . . . . . . . . . . . . .   33   39
     5.9. PadN Option . . . . . . . . . . . . . . . . . . . . . . .   34   40
 6. Detailed Operation                                                35                                                41

     6.1. General Packet Processing . . . . . . . . . . . . . . . .   35   41
           6.1.1. Originating a Packet  . . . . . . . . . . . . . .   35   41
           6.1.2. Adding a DSR Header to a Packet . . . . . . . . .   35   41
           6.1.3. Adding a DSR Source Route Option to a Packet  . . . .   36   42
           6.1.4. Receiving Processing a Received Packet  . . . . . . . . . . . . . . .   36   43
           6.1.5. Processing a Received DSR Source Route Option . . . .   38   45
     6.2. Route Discovery Processing  . . . . . . . . . . . . . . .   40   48
           6.2.1. Originating a Route Request . . . . . . . . . . .   40   48
           6.2.2. Processing a Received Route Request Option  . . .   42   50
           6.2.3. Generating a Route Replies Reply using the Route Cache  .   43   51
           6.2.4. Originating a Route Reply . . . . . . . . . . . .   44   54
           6.2.5. Processing a Received Route Reply Option  . . . . . . . . .   46   55
     6.3. Route Maintenance Processing  . . . . . . . . . . . . . .   47   57
           6.3.1. Using Network-Layer Link-Layer Acknowledgments  . . . . . . .   47 .   57
           6.3.2. Using Link Layer Passive Acknowledgments . . . . . . . .   48 . .   58
           6.3.3. Using Network-Layer Acknowledgments . . . . . . .   59
           6.3.4. Originating a Route Error . . . . . . . . . . . .   48
           6.3.4.   62
           6.3.5. Processing a Received Route Error Option  . . . . . . . . .   49
           6.3.5.   63
           6.3.6. Salvaging a Packet  . . . . . . . . . . . . . . .   49   64

 7. Protocol Constants                                                         50 and Configuration Variables                    66

 8. IANA Considerations                                               51                                               67

 9. Security Considerations                                           52                                           68

Appendix A. Link-MaxLife Cache Description                            69

Appendix B. Location of DSR in the ISO Network Reference Model        53        71

Appendix B. C. Implementation and Evaluation Status                      54                      72

Changes from Previous Version of the Draft                            73

Acknowledgements                                                      55                                                      76

References                                                            56                                                            77

Chair's Address                                                       59                                                       80

Authors' Addresses                                                    60                                                    81

1. Introduction

   The Dynamic Source Routing protocol (DSR) [12, 13] [13, 14] is a simple and
   efficient routing protocol designed specifically for use in multi-hop
   wireless ad hoc networks of mobile nodes.  Using DSR, the network
   is completely self-organizing and self-configuring, requiring no
   existing network infrastructure or administration.  Network nodes
   cooperate to forward packets for each other to allow communication
   over multiple "hops" between nodes not directly within wireless
   transmission range of one another.  As nodes in the network move
   about or join or leave the network, and as wireless transmission
   conditions such as sources of interference change, all routing is
   automatically determined and maintained by the DSR routing protocol.
   Since the number or sequence of intermediate hops needed to reach any
   destination may change at any time, the resulting network topology
   may be quite rich and rapidly changing.

   The DSR protocol allows nodes to dynamically discover a source
   route across multiple network hops to any destination in the ad hoc
   network.  Each data packet sent then carries in its header the
   complete, ordered list of nodes through which the packet will pass,
   allowing packet routing to be trivially loop-free and avoiding the
   need for up-to-date routing information in the intermediate nodes
   through which the packet is forwarded.  By including this source
   route in the header of each data packet, other nodes forwarding or
   overhearing any of these packets may can also easily cache this routing
   information for future use.

   In designing DSR, we sought to create a routing protocol that had
   very low overhead yet was able to react very quickly to changes in
   the network.  The DSR protocol provides highly reactive service in
   order to help ensure successful delivery of data packets in spite of
   node movement or other changes in network conditions.

   The DSR protocol is composed of two main mechanisms that work
   together to allow the discovery and maintenance of source routes in
   the ad hoc network:

    -  Route Discovery is the mechanism by which a node S wishing to
       send a packet to a destination node D obtains a source route
       to D.  Route Discovery is used only when S attempts to send a
       packet to D and does not already know a route to D.

    -  Route Maintenance is the mechanism by which node S is able
       to detect, while using a source route to D, if the network
       topology has changed such that it can no longer use its route
       to D because a link along the route no longer works.  When Route
       Maintenance indicates a source route is broken, S can attempt to
       use any other route it happens to know to D, or can invoke Route
       Discovery again to find a new route for subsequent packets to D.

       Route Maintenance for this route is used only when S is actually
       sending packets to D.

   In DSR, Route Discovery and Route Maintenance each operate entirely
   "on demand".  In particular, unlike other protocols, DSR requires no
   periodic packets of any kind at any level layer within the network.  For
   example, DSR does not use any periodic routing advertisement, link
   status sensing, or neighbor detection packets, and does not rely on
   these functions from any underlying protocols in the network.  This
   entirely on-demand behavior and lack of periodic activity allows
   the number of overhead packets caused by DSR to scale all the way
   down to zero, when all nodes are approximately stationary with
   respect to each other and all routes needed for current communication
   have already been discovered.  As nodes begin to move more or
   as communication patterns change, the routing packet overhead of
   DSR automatically scales to only that needed to track the routes
   currently in use.  Network topology changes not affecting routes
   currently in use are ignored and do not cause reaction from the
   protocol.

   In response to a single Route Discovery (as well as through routing
   information from other packets overheard), a node may learn and cache
   multiple routes to any destination.  This allows the reaction to
   routing changes to be much more rapid, since a node with multiple
   routes to a destination can try another cached route if the one it
   has been using should fail.  This caching of multiple routes also
   avoids the overhead of needing to perform a new Route Discovery each
   time a route in use breaks.

   The operation of both Route Discovery and Route Maintenance in DSR
   are designed to allow uni-directional links and asymmetric routes
   to be easily supported.  In particular, as noted in Section 2, in
   wireless networks, it is possible that a link between two nodes may
   not work equally well in both directions, due to differing antenna
   or propagation patterns or sources of interference.  DSR allows such
   uni-directional links to be used when necessary, improving overall
   performance and network connectivity in the system.

   This document specifies the operation of the DSR protocol for
   routing unicast IP IPv4 packets in multi-hop wireless ad hoc networks.
   Advanced, optional features, such as Quality of Service (QoS) support
   and efficient multicast routing, and operation of DSR with IPv6 [6],
   are covered in other documents.  The specification of DSR in this
   document provides a compatible base on which such features can be
   added, either independently or by integration with the DSR operation
   specified here.

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [4].

2. Assumptions

   We assume in this document that all nodes wishing to communicate with
   other nodes within the ad hoc network are willing to participate
   fully in the protocols of the network.  In particular, each node
   participating in the ad hoc network SHOULD also be willing to forward
   packets for other nodes in the network.

   The diameter of an ad hoc network is the minimum number of hops
   necessary for a packet to reach from any node located at one extreme
   edge of the ad hoc network to another node located at the opposite
   extreme.  We assume that this diameter will often be small (e.g.,
   perhaps 5 or 10 hops), but may often be greater than 1.

   Packets may be lost or corrupted in transmission on the wireless
   network.  We assume that a node receiving a corrupted packet can
   detect the error and discard the packet.

   Nodes within the ad hoc network MAY move at any time without notice,
   and MAY even move continuously, but we assume that the speed with
   which nodes move is moderate with respect to the packet transmission
   latency and wireless transmission range of the particular underlying
   network hardware in use.  In particular, DSR can support very
   rapid rates of arbitrary node mobility, but we assume that nodes do
   not continuously move so rapidly as to make the flooding of every
   individual data packet the only possible routing protocol.

   A common feature of many network interfaces, including most current
   LAN hardware for broadcast media such as wireless, is the ability
   to operate the network interface in "promiscuous" receive mode.
   This mode causes the hardware to deliver every received packet to
   the network driver software without filtering based on link-layer
   destination address.  Although we do not require this facility, some
   of our optimizations can take advantage of its availability.  Use
   of promiscuous mode does increase the software overhead on the CPU,
   but we believe that wireless network speeds are more the inherent
   limiting factor to performance in current and future systems; we also
   believe that portions of the protocol are suitable for implementation
   directly within a programmable network interface unit to avoid this
   overhead on the CPU [13]. [14].  Use of promiscuous mode may also increase
   the power consumption of the network interface hardware, depending
   on the design of the receiver hardware, and in such cases, DSR can
   easily be used without the optimizations that depend on promiscuous
   receive mode, or can be programmed to only periodically switch the
   interface into promiscuous mode.  Use of promiscuous receive mode is
   entirely optional.

   Wireless communication ability between any pair of nodes may at
   times not work equally well in both directions, due for example to
   differing antenna or propagation patterns or sources of interference
   around the two nodes [1, 17]. 18].  That is, wireless communications
   between each pair of nodes will in many cases be able to operate
   bi-directionally, but at times the wireless link between two nodes
   may be only uni-directional, allowing one node to successfully send
   packets to the other while no communication is possible in the
   reverse direction.  Although many routing protocols operate correctly
   only over bi-directional links, DSR can successfully discover and
   forward packets over paths that contain uni-directional links.
   Some MAC protocols, however, such as MACA [16], [17], MACAW [2], or IEEE
   802.11 [10], [11], limit unicast data packet transmission to bi-directional
   links, due to the required bi-directional exchange of RTS and CTS
   packets in these protocols and due to the link-level link-layer acknowledgement
   feature in IEEE 802.11; when used on top of MAC protocols such as
   these, DSR can take advantage of additional optimizations, such as
   the easy ability to reverse a source route to obtain a route back to the
   origin of the original route.

   The IP address used by a node using the DSR protocol MAY be assigned
   by any mechanism (e.g., static assignment or use of DHCP for dynamic
   assignment [8]), [7]), although the method of such assignment is outside
   the scope of this specification.

3. DSR Protocol Overview

3.1. Basic DSR Route Discovery

   When some source node originates a new packet addressed to some
   destination node, the source node places in the header of the packet
   a source route giving the sequence of hops that the packet is to
   follow on its way to the destination.  Normally, the sender will
   obtain a suitable source route by searching its "Route Cache" of
   routes previously learned, but learned; if no route is found in its cache, it will
   initiate the Route Discovery protocol to dynamically find a new route
   to this destination node.  In this case, we call the source node
   the "initiator" and the destination node the "target" of the Route
   Discovery.

   For example, suppose a node A is attempting to discover a route to
   node E.  The Route Discovery initiated by node A in this example
   would proceed as follows:

            ^    "A"    ^   "A,B"   ^  "A,B,C"  ^ "A,B,C,D"
            |   id=2    |   id=2    |   id=2    |   id=2
         +-----+     +-----+     +-----+     +-----+     +-----+
         |  A  |---->|  B  |---->|  C  |---->|  D  |---->|  E  |
         +-----+     +-----+     +-----+     +-----+     +-----+
            |           |           |           |
            v           v           v           v

   To initiate the Route Discovery, node A transmits a "Route
   Request" as a single local broadcast packet, which is received by
   (approximately) all nodes currently within wireless transmission
   range of A, including node B in this example.  Each Route Request
   identifies the initiator and target of the Route Discovery, and
   also contains a unique request identification (2, in this example),
   determined by the initiator of the Request.  Each Route Request also
   contains a record listing the address of each intermediate node
   through which this particular copy of the Route Request has been
   forwarded.  This route record is initialized to an empty list by the
   initiator of the Route Discovery.  In this example, the route record
   initially lists only node A.

   When another node receives this Route Request (such as node B in this
   example), if it is the target of the Route Discovery, it returns
   a "Route Reply" to the initiator of the Route Discovery, giving
   a copy of the accumulated route record from the Route Request;
   when the initiator receives this Route Reply, it caches this route
   in its Route Cache for use in sending subsequent packets to this
   destination.

   Otherwise, if this node receiving the Route Request has recently seen
   another Route Request message from this initiator bearing this same
   request identification and target address, or if this node's own
   address is already listed in the route record in the Route Request,
   this node discards the Request.  Otherwise, this node appends its
   own address to the route record in the Route Request and propagates
   it by transmitting it as a local broadcast packet (with the same
   request identification).  In this example, node B broadcast the Route
   Request, which is received by node C; nodes C and D each also, in
   turn, broadcast the Request, resulting in a copy of the Request being
   received by node E.

   In returning the Route Reply to the initiator of the Route Discovery,
   such as in this example, node E replying back to node A, node E will
   typically examine its own Route Cache for a route back to A, and if
   found, will use it for the source route for delivery of the packet
   containing the Route Reply.  Otherwise, E SHOULD perform its own
   Route Discovery for target node A, but to avoid possible infinite
   recursion of Route Discoveries, it MUST piggyback this Route Reply
   on the packet containing its own Route Request for A.  It is also
   possible to piggyback other small data packets, such as a TCP SYN
   packet [25], [28], on a Route Request using this same mechanism.

   Node E could instead simply reverse the sequence of hops in the route
   record that it is trying to send in the Route Reply, and use this as
   the source route on the packet carrying the Route Reply itself.  For
   MAC protocols such as IEEE 802.11 that require a bi-directional frame
   exchange as part of the MAC protocol [10], this [11], the discovered source
   route reversal
   is preferred, as it avoids MUST be reversed in this way to return the overhead of a possible second Route Discovery, and Reply since it
   tests the discovered route to ensure it is bi-directional before the
   Route Discovery initiator begins using the
   route. route; this route reversal
   also avoids the overhead of a possible second Route Discovery.
   However, this route reversal technique will prevent the discovery
   of routes using uni-directional links.  In links, and in wireless environments
   where the use of uni-directional links is permitted, such routes may
   in some cases be more efficient than those with only bi-directional
   links, or they may be the only way to achieve connectivity to the
   target node.

   When initiating a Route Discovery, the sending node saves a copy of
   the original packet (that triggered the Discovery) in a local buffer
   called the "Send Buffer".  The Send Buffer contains a copy of each
   packet that cannot be transmitted by this node because it does not
   yet have a source route to the packet's destination.  Each packet in
   the Send Buffer is logically associated with the time that it was
   placed into the Send Buffer and is discarded after residing in the
   Send Buffer for some timeout period; if necessary for preventing the
   Send Buffer from overflowing, a FIFO or other replacement strategy
   MAY also be used to evict packets even before they expire.

   While a packet remains in the Send Buffer, the node SHOULD
   occasionally initiate a new Route Discovery for the packet's
   destination address.  However, the node MUST limit the rate at which
   such new Route Discoveries for the same address are initiated, since
   it is possible that the destination node is not currently reachable.
   In particular, due to the limited wireless transmission range and the
   movement of the nodes in the network, the network may at times become
   partitioned, meaning that there is currently no sequence of nodes
   through which a packet could be forwarded to reach the destination.
   Depending on the movement pattern and the density of nodes in the
   network, such network partitions may be rare or may be common.

   If a new Route Discovery was initiated for each packet sent by a
   node in such a partitioned network, a large number of unproductive
   Route Request packets would be propagated throughout the subset
   of the ad hoc network reachable from this node.  In order to
   reduce the overhead from such Route Discoveries, a node MUST SHOULD use
   an exponential back-off algorithm to limit the rate at which it
   initiates new Route Discoveries for the same target.  If target, doubling the node attempts to send
   additional data
   timeout between each successive Discovery initiated for the same
   target.  If the node attempts to send additional data packets to this
   same destination node more frequently than this limit, the subsequent
   packets SHOULD be buffered in the Send Buffer until a Route Reply is
   received giving a route to this destination, but the node MUST NOT
   initiate a new Route Discovery until the minimum allowable interval
   between new Route Discoveries for this target has been reached.  This
   limitation on the maximum rate of Route Discoveries for the same
   target is similar to the mechanism required by Internet nodes to
   limit the rate at which ARP Requests are sent for any single target
   IP address [3].

3.2. Basic DSR Route Maintenance

   When originating or forwarding a packet using a source route, each
   node transmitting the packet is responsible for confirming that the
   packet has been received by the next hop node along the source route; the
   packet SHOULD be retransmitted (up to a maximum number of attempts)
   until this confirmation of receipt is received.  For example, in the
   situation shown below, node A has originated a packet for node E
   using a source route through intermediate nodes B, C, and D:

         +-----+     +-----+     +-----+     +-----+     +-----+
         |  A  |---->|  B  |---->|  C  |--x  |-->? |  D  |     |  E  |
         +-----+     +-----+     +-----+     +-----+     +-----+

   In this case, node A is responsible for receipt of the packet at B,
   node B is responsible for receipt at C, node C is responsible for
   receipt at D, and node D is responsible for receipt finally at the
   destination E.

   This confirmation of receipt in many cases may be provided at no cost
   to DSR, either as an existing standard part of the MAC protocol in
   use (such as the link-level link-layer acknowledgement frame defined by IEEE
   802.11 [10]), [11]), or by a "passive acknowledgement" [15] [16] (in which,
   for example, B confirms receipt at C by overhearing C transmit
   the packet when forwarding it on to D).  If neither of these
   confirmation mechanisms are available, the node transmitting the
   packet can explicitly request a DSR-specific software acknowledgement
   be returned by the next hop; node along the route; this software
   acknowledgement will normally be transmitted directly to the sending
   node, but if the link between these two nodes is uni-directional,
   this software acknowledgement may could travel over a different,
   multi-hop path.

   If

   At the original sender of a packet if no receipt confirmation is
   received after the packet sender has been retransmitted the packet the maximum
   number of attempts by some hop, to the first intermediate node on the source
   route, then the sender determines that this first hop of the route
   is currently "broken".  For example, in the situation shown above,
   if the sender, node A, is unable to deliver the packet to the next
   node B, then A determines that the hop from A to B is broken.  In
   this case, node A removes this link from its Route Cache and removes
   the DSR routing information that it had previously added to the
   packet.  Node A then again searches its Route Cache for a route to
   the destination node, and if no route is found in the cache, uses the
   Route Discovery protocol again to dynamically discover a new route
   for the packet.

   At an intermediate node forwarding a packet, if no receipt
   confirmation is received after the node has retransmitted the packet
   the maximum number of attempts, this node SHOULD return a "Route
   Error" to the original sender of the packet, identifying the link
   over which the packet could not be forwarded.  For example, in the example
   situation shown above, if C is unable to deliver the packet to the
   next hop node D, then C returns a Route Error to A, stating that the link
   from C to D is currently "broken".  Node A then removes this broken
   link from its cache; any retransmission of the original packet can
   be performed by upper layer protocols such as TCP, if necessary.
   For sending such a retransmission or other packets to this same
   destination E, if A has in its Route Cache another route to E
   (for example, from additional Route Replies from its earlier Route
   Discovery, or from having overheard sufficient routing information
   from other packets), it can send the packet using the new route
   immediately.  Otherwise, it SHOULD perform a new Route Discovery for
   this target (subject to the exponential back-off described in Section 3.1).

3.3. Additional Route Discovery Features

3.3.1. Caching Overheard Routing Information

   A node forwarding or otherwise overhearing any packet MAY SHOULD add the all
   usable routing information from that packet to its own Route Cache.  In
   particular, the source route used
   The usefulness of routing information in a data packet, packet depends on the accumulated
   route record in a Route Request, or
   directionality characteristics of the route physical medium (Section 2), as
   well as the MAC protocol being returned used.  Specifically, three distinct
   cases are possible:

    -  Links in a
   Route Reply MAY all be cached by any node.  Routing information from
   any of these the network frequently are capable of operating only
       uni-directionally (not bi-directionally), and the MAC protocol
       in use in the network is capable of transmitting unicast packets received
       over uni-directional links.

    -  Links in the network occasionally are capable of operating
       only uni-directionally (not bi-directionally), but this
       uni-directional restriction on any link is not persistent, almost
       all links are physically bi-directional, and the MAC protocol in
       use in the network is capable of transmitting unicast packets
       over uni-directional links.

    -  The MAC protocol in use in the network is not capable of
       transmitting unicast packets over uni-directional links;
       only bi-directional links can be cached, used by the MAC protocol for
       transmitting unicast packets.  For example, the IEEE 802.11
       Distributed Coordination Function (DCF) MAC protocol [11]
       is capable of transmitting a unicast packet only over a
       bi-directional link, since the MAC protocol requires the return
       of a link-level acknowledgement packet from the receiver and also
       optionally requires the bi-directional exchange of an RTS and CTS
       packet between the transmitter and receiver nodes.

   In the first case above, for example, the source route used in a data
   packet, the accumulated route record in a Route Request, or the route
   being returned in a Route Reply SHOULD all be cached by any node in
   the "forward" direction; any node SHOULD cache this information from
   any such packet received, whether the packet was addressed to this
   node, sent to a broadcast (or multicast) MAC address, or received overheard
   while the node's network interface is in promiscuous mode.

   One limitation, however, on caching of such overheard routing
   information is  However,
   the possible presence "reverse" direction of uni-directional the links identified in the
   ad hoc network (Section 2). such packet
   headers SHOULD NOT be cached.

   For example, in the situation shown below, node A is using a source
   route to communicate with node E:

         +-----+     +-----+     +-----+     +-----+     +-----+
         |  A  |---->|  B  |---->|  C  |---->|  D  |---->|  E  |
         +-----+     +-----+     +-----+     +-----+     +-----+
                                    ^
                                    |
         +-----+     +-----+     +-----+     +-----+     +-----+
         |  V  |---->|  W  |---->|  X  |---->|  Y  |---->|  Z  |
         +-----+     +-----+     +-----+     +-----+     +-----+

   As node C forwards a data packet along the route from A to E, it
   MAY
   SHOULD add to its cache the presence of the "forward" direction
   links that it learns from the headers of these packets, from itself
   to D and from D to E.  However,  Node C SHOULD NOT, in this case, cache the
   "reverse" direction of the links identified in the these packet headers,
   from itself back to B and from B to A, may not work for it since these links might be
   uni-directional.
   If C knows that

   In the links are second case above, in fact bi-directional, for example due
   to which links may occasionally operate
   uni-directionally, the MAC protocol in use, it could cache them but otherwise links described above SHOULD
   not.

   Likewise, node V be cached in the example above both
   directions.  Furthermore, in this case, if node X overhears (e.g.,
   through promiscuous mode) a packet transmitted by node C that is
   using a different source route to communicate with node Z.  If node C overhears from node X
   transmitting a data packet to forward it A to Y (from V), E, node C X SHOULD
   consider whether the cache all of
   these links involved can be known to be bi-directional
   or not before caching them.  If as well, also including the link from X to C (over which this
   data packet was received) can be known to be bi-directional, then C
   MAY cache X over which
   it overheard the link from itself to X, packet.

   In the link from X to Y, and final case, in which the
   link from Y to Z.  If all MAC protocol requires physical
   bi-directionality for unicast operation, links can be assumed to from a source
   route SHOULD be bi-directional,
   C MAY cached in both directions, except when the packet
   also cache contains a Route Reply, in which case only the links from X to W and from W to V.  Similar
   considerations apply to already
   traversed in this source route SHOULD be cached, but the routing information that might links not
   yet traversed in this route SHOULD NOT be learned
   from forwarded or otherwise overheard Route Request or Route Reply
   packets. cached.

3.3.2. Replying to Route Requests using Cached Routes

   A node receiving a Route Request for which it is not the target,
   searches its own Route Cache for a route to the target of the
   Request.  If found, the node generally returns a Route Reply to the
   initiator itself rather than forwarding the Route Request.  In the
   Route Reply, this node sets the route record to list the sequence of
   hops over which this copy of the Route Request was forwarded to it,
   concatenated with the source route to this target obtained from its
   own Route Cache.

   However, before transmitting a Route Reply packet that was generated
   using information from its Route Cache in this way, a node MUST
   verify that the resulting route being returned in the Route Reply,
   after this concatenation, contains no duplicate nodes listed in the
   route record.  For example, the figure below illustrates a case in
   which a Route Request for target E has been received by node F, and
   node F already has in its Route Cache a route from itself to E:

         +-----+     +-----+                 +-----+     +-----+
         |  A  |---->|  B  |-               >|  D  |---->|  E  |
         +-----+     +-----+ \             / +-----+     +-----+
                              \           /
                               \ +-----+ /
                                >|  C  |-
                                 +-----+
                                   | ^
                                   v |
           Route Request         +-----+
           Route: A - B - C - F  |  F  |  Cache: C - D - E
                                 +-----+

   The concatenation of the accumulated route record from the Route
   Request and the cached route from F's Route Cache would include a
   duplicate node in passing from C to F and back to C.

   Node F in this case could attempt to edit the route to eliminate the
   duplication, resulting in a route from A to B to C to D and on to E,
   but in this case, node F would not be on the route that it returned
   in its own Route Reply.  DSR Route Discovery prohibits node F
   from returning such a Route Reply from its cache for two reasons.  First, cache; this limitation prohibition
   increases the probability that the resulting route is valid, since
   node F in this case should have received a Route Error if the route
   had previously stopped working.  Second,  Furthermore, this
   limitation prohibition
   means that a future Route Error traversing the route is very likely
   to pass through any node that sent the Route Reply for the route
   (including node F), which helps to ensure that stale data is removed
   from caches (such as at F) in a timely manner.  Otherwise, manner; otherwise, the next
   Route Discovery initiated by A might also be contaminated by a Route
   Reply from F containing the same stale route.  If the Route
   Request does not meet these restrictions, the node (node F in F, due to this
   example) discards the
   restriction on returning a Route Request rather than replying to it or
   propagating it. Reply based on information from its
   Route Cache, does not return such a Route Reply, node F propagates
   the Route Request normally.

3.3.3. Preventing Route Reply Storms

   The ability for nodes to reply to a Route Request based on
   information in their Route Caches, as described in Section 3.3.2,
   could result in a possible Route Reply "storm" in some cases.  In
   particular, if a node broadcasts a Route Request for a target node
   for which the node's neighbors have a route in their Route Caches,
   each neighbor may attempt to send a Route Reply, thereby wasting
   bandwidth and possibly increasing the number of network collisions in
   the area.

   For example, the figure below shows a situation in which nodes B, C,
   D, E, and F all receive A's Route Request for target G, and each has
   the indicated route cached for this target:

                +-----+                 +-----+
                |  D  |<               >|  C  |
                +-----+ \             / +-----+
      Cache: C - B - G   \           /  Cache: B - G
                          \ +-----+ /
                           -|  A  |-
                            +-----+\     +-----+     +-----+
                             |   |  \--->|  B  |     |  G  |
                            /     \      +-----+     +-----+
                           /       \     Cache: G
                          v         v
                    +-----+         +-----+
                    |  E  |         |  F  |
                    +-----+         +-----+
               Cache: F - B - G     Cache: B - G

   Normally, each of these nodes would all attempt to reply from their its own
   Route Caches, Cache, and they would thus all send their Route Replies at
   about the same time, since they all received the broadcast Route
   Request at about the same time.  Such simultaneous replies Route Replies
   from different nodes all receiving the Route Request may cause local
   congestion in the wireless network and may create packet collisions
   among some or all of these Replies and may cause local congestion in if the
   wireless network. MAC protocol in use does
   not provide sufficient collision avoidance for these packets.  In
   addition, it will often be the case that the different replies will
   indicate routes of different lengths, as shown in this example.

   If

   In order to reduce these effects, if a node can put its network
   interface into promiscuous receive mode, it SHOULD MAY delay sending its
   own Route Reply for a short period, while listening to see if the
   initiating node begins using a shorter route first.  That is,  Specifically,
   this node SHOULD MAY delay sending its own Route Reply for a random period

      d = H * (h - 1 + r)

   where h is the length in number of network hops for the route to be
   returned in this node's Route Reply, r is a random floating point
   number between 0 and 1, and H is a small constant delay (at least
   twice the maximum wireless link propagation delay) to be introduced
   per hop.  This delay effectively randomizes the time at which each
   node sends its Route Reply, with all nodes sending Route Replies
   giving routes of length less than h sending their Replies before this
   node, and all nodes sending Route Replies giving routes of length
   greater than h sending their Replies after this node.

   Within the delay period, this node promiscuously receives all
   packets, looking for data packets from the initiator of this Route
   Discovery destined for the target of the Discovery.  If such a data
   packet received by this node during the delay period uses a source
   route of length less than or equal to h, this node may infer that the
   initiator of the Route Discovery has already received a Route Reply
   giving an equally good or better route.  In this case, this node
   SHOULD cancel its delay timer and SHOULD NOT send its Route Reply for
   this Route Discovery.

3.3.4. Route Request Hop Limits

   Each Route Request message contains a "hop limit" that may be used
   to limit the number of intermediate nodes allowed to forward that
   copy of the Route Request.  This hop limit is implemented using the
   Time-to-Live (TTL) field in the IP header of the packet carrying
   the Route Request.  As the Request is forwarded, this limit is
   decremented, and the Request packet is discarded if the limit reaches
   zero before finding the target.  This Route Request hop limit can be
   used to implement a variety of algorithms for controlling the spread
   of a Route Request during a Route Discovery attempt.

   For example, a node MAY send use this hop limit to implement a
   "non-propagating" Route Request as an initial phase of a Route
   Discovery.  A node using this technique sends its first Route Request
   attempt for some target node using a hop limit of 1, such that any
   node receiving the initial transmission of the Route Request will
   not forward the Request to other nodes by rebroadcasting re-broadcasting it.  This
   form of Route Request is called a "non-propagating" Route Request.  It Request;
   it provides an inexpensive method for determining if the target is
   currently a neighbor of the initiator or if a neighbor node has a
   route to the target cached (effectively using the neighbors' Route
   Caches as an extension of the initiator's own Route Cache).  If no
   Route Reply is received after a short timeout, then the node sends a
   "propagating" Route Request (i.e., with no hop limit) for the target
   node.

   As another example, a node MAY be sent.

   Another possible use of the this hop limit in a Route Request is to implement an
   "expanding ring" search for the target [13].  For
   example, a [14].  A node could send using this
   technique sends an initial non-propagating Route Request as described
   above; if no Route Reply is received for it, the node
   could initiate originates
   another Route Request with a hop limit of 2.  For each Route Request initiated,
   originated, if no Route Reply is received for it, the node could double doubles
   the hop limit used on the previous attempt, to progressively explore
   for the target node without allowing the Route Request to propagate
   over the entire network.  However, this expanding ring search
   approach could have the effect of increasing the average latency of
   Route Discovery, since multiple Discovery attempts and timeouts may
   be needed before discovering a route to the target node.

3.4. Additional Route Maintenance Features

3.4.1. Packet Salvaging

   After sending

   When an intermediate node forwarding a Route Error message as part of packet detects through Route
   Maintenance
   as described in Section 3.2, a node MAY attempt to "salvage" the
   data packet that caused the Route Error rather than discarding next hop along the
   packet.  To attempt to salvage a packet, route for that packet is
   broken, if the node sending a Route
   Error searches its own Route Cache for a has another route from itself to the packet's destination of the packet causing the Error.  If such a route is
   found, in
   its Route Cache, the node MAY salvage SHOULD "salvage" the packet after returning rather than
   discarding it.  To salvage a packet, the Route
   Error by replacing node replaces the original
   source route on the packet with the route from its Route Cache.  The
   node then forwards the packet to the next node indicated along this
   source route.  For example, in the situation shown in the example of
   Section 3.2, if node C has another route cached to node E, it can
   salvage the packet by replacing the original route in the packet with
   this new route from its own Route Cache, rather than discarding the
   packet.

   When salvaging a packet in this way, packet, a count is maintained in the packet of the
   number of times that it has been salvaged, to prevent a single packet
   from being salvaged endlessly.  Otherwise, it could be possible for
   the packet to enter a routing loop, as different nodes repeatedly
   salvage the packet and replace the source route on the packet with
   routes to each other.

3.4.2. Automatic Route Shortening

   Source routes

   As described in use MAY be automatically shortened if one or more Section 3.2, an intermediate hops in the route become no longer necessary.  This
   mechanism of automatically shortening routes in use is somewhat
   similar to the use of passive acknowledgements [15].  In particular,
   if a node is able to overhear a packet carrying a source route (e.g.,
   by operating its network interface node, such as in promiscuous receive mode), then this node examines the unused portion of
   case, that detects through Route Maintenance that source route.  If this
   node is not the intended next hop for the packet but is named in
   the later unused portion of the packet's source route, then it can
   infer that the intermediate nodes before itself in along
   the source route
   are no longer needed in the route.  For example, the figure below
   illustrates an example in which node D has overheard for a data packet
   being transmitted from B to C, for later that it is forwarding to D and to E:

         +-----+     +-----+     +-----+     +-----+     +-----+
         |  A  |---->|  B  |---->|  C  |     |  D  |     |  E  |
         +-----+     +-----+     +-----+     +-----+     +-----+
                        \                       ^
                         \                     /
                          ---------------------

   In this case, this is broken, the node (node D) returns also
   SHOULD return a "gratuitous" Route Reply Error to the original sender of the packet (node A).  The Route Reply
   gives the shorter route as the concatenation of packet,
   identifying the portion of link over which the
   original source route up through packet could not be forwarded.
   If the node that transmitted sends this Route Error, it SHOULD originate the
   overheard packet (node B), plus the suffix of the original source
   route beginning with Route
   Error before salvaging the packet.

3.4.2. Queued Packets Destined over a Broken Link

   When an intermediate node returning the gratuitous forwarding a packet detects through Route Reply
   (node D). In this example,
   Maintenance that the next-hop link along the route returned for that packet
   is broken, in the gratuitous Route
   Reply message sent from D addition to A gives the new route handling that packet as the sequence of
   hops from A to B to D to E.

3.4.3. Increased Spreading of defined for Route Error Messages

   When a source
   Maintenance, the node receives a Route Error for SHOULD also handle in a data packet similar way any pending
   packets that it originated, has queued that are destined over this source new broken
   link.  Specifically, the node propagates this Route Error to its
   neighbors by piggybacking it on SHOULD search its next Route Request.  In this way,
   stale information in Network Interface
   Queue and Retransmission Buffer (Section 4.5) for packets for which
   the caches of nodes around next-hop link is this source new broken link.  For each such packet
   currently queued at this node, the node will
   not generate Route Replies SHOULD process that contain packet as
   follows:

    -  Remove the same invalid link packet from the node's Network Interface Queue and
       Retransmission Buffer and stop any retransmission activity for
   which this source node received
       the packet.

    -  Originate a Route Error.

   For example, in the situation shown in Error for this packet to the example original sender of
       the packet, using the procedure described in Section 3.2, 6.3.4, as if
       the node A learns from had already reached the Route Error message from C, maximum number of retransmission
       attempts for that the link
   from C to D is currently broken.  It thus removes this link from
   its own packet for Route Cache and initiates Maintenance.  However, in
       sending such Route Errors for queued packets in response to a
       single new broken link detected, the node SHOULD send no more
       than one Route Discovery (if it Error to each original sender of any of these
       packets.

    -  If the node has
   no other another route to E the packet's IP
       Destination Address in its Route Cache).  On Cache, the node SHOULD
       salvage the Route Request packet initiating this Route Discovery, as described in Section 6.3.6.  Otherwise, the
       node A piggybacks a copy
   of this Route Error, ensuring that SHOULD discard the packet.

3.4.3. Automatic Route Error spreads well to
   other nodes, and guaranteeing that any Route Reply that it receives
   (including those from other node's Route Caches) Shortening

   Source routes in use MAY be automatically shortened if one or more
   intermediate nodes in response to this
   Route Request does not contain a route that assumes the existence of
   this broken link.

4. Conceptual Data Structures route become no longer necessary.  This document describes the operation
   mechanism of the DSR protocol automatically shortening routes in terms use is somewhat
   similar to the use of passive acknowledgements [16].  In particular,
   if a number of conceptual data structures.  This section describes
   each of these data structures and provides an overview of node is able to overhear a packet carrying a source route (e.g.,
   by operating its use network interface in promiscuous receive mode), then
   this node examines the protocol.  In an implementation unexpended portion of that source route.  If
   this node is not the protocol, these data
   structures MAY be implemented in any manner consistent with intended next-hop destination for the
   external behavior described packet
   but is named in this document.

4.1. Route Cache

   All routing information the later unexpended portion of the packet's source
   route, then it can infer that the intermediate nodes before itself in
   the source route are no longer needed by a node participating in the route.  For example, the
   figure below illustrates an ad hoc
   network using DSR is stored example in that node's Route Cache.  Each which node in
   the network maintains its own Route Cache. D has overheard a
   data packet being transmitted from B to C, for later forwarding to D
   and to E:

         +-----+     +-----+     +-----+     +-----+     +-----+
         |  A  |---->|  B  |---->|  C  |     |  D  |     |  E  |
         +-----+     +-----+     +-----+     +-----+     +-----+
                        \                       ^
                         \                     /
                          ---------------------

   In this case, this node adds information (node D) SHOULD return a "gratuitous" Route
   Reply to its the original sender of the packet (node A).  The Route Cache
   Reply gives the shorter route as it learns the concatenation of new links between nodes in the
   ad hoc network; for example, a portion of
   the original source route up through the node may learn that transmitted the
   overheard packet (node B), plus the suffix of the original source
   route beginning with the node returning the gratuitous Route Reply
   (node D). In this example, the route returned in the gratuitous Route
   Reply message sent from D to A gives the new links when it
   receives a packet carrying either route as the sequence of
   hops from A to B to D to E.

   When deciding whether to return a gratuitous Route Reply or a DSR Routing
   header.  Likewise, in this way,
   a node removes MAY factor in additional information from its Route Cache as
   it learns beyond the fact that existing links in it
   was able to overhear the ad hoc network have broken; for packet.  For example, the node MAY decide to
   return the gratuitous Route Reply only when the overheard packet is
   received with a signal strenth or signal-to-noise ratio above some
   specific threshold.  In addition, each node may learn of maintains a broken link when Gratuitous
   Route Reply Table, as described in Section 4.4, to limit the rate at
   which it receives originates gratuitous Route Replies for the same returned
   route.

3.4.4. Increased Spreading of Route Error Messages

   When a packet
   carrying source node receives a Route Error or through the link-layer retransmission
   mechanism reporting a failure in forwarding for a data packet that
   it originated, this source node propagates this Route Error to its next-hop
   destination.

   It is possible to interface a DSR network with other networks,
   external to
   neighbors by piggybacking it on its next Route Request.  In this DSR network.  Such external networks may, for
   example, be the Internet, or may be other ad hoc networks routed
   with a routing protocol other than DSR.  Such external networks may
   also be other DSR networks that are treated as external networks way,
   stale information in order to improve scalability.  The complete handling of such
   external networks is beyond the scope caches of nodes around this document.  However, source node will
   not generate Route Replies that contain the same invalid link for
   which this document specifies a minimal set source node received the Route Error.

   For example, in the situation shown in the example of requirements and features
   necessary Section 3.2,
   node A learns from the Route Error message from C, that the link
   from C to allow nodes only implementing D is currently broken.  It thus removes this specification to
   interoperate correctly with nodes implementing interfaces to such
   external networks.  This minimal set of requirements and features
   involve the First Hop External (F) and Last Hop External (L)
   bits in a Source link from
   its own Route option (Section 5.7) Cache and initiates a new Route Reply
   option (Section 5.3) Discovery (if it has
   no other route to E in a packet's DSR header (Section 5).  These
   requirements also include its Route Cache).  On the addition of an External flag bit
   tagging each Route Request
   packet initiating this Route Discovery, node in the A piggybacks a copy
   of this Route Cache, copied from the First Hop
   External (F) and Last Hop External (L) bits in Error, ensuring that the Source Route
   option or Error spreads well to
   other nodes, and guaranteeing that any Route Reply option that it receives
   (including those from which the link to this node was
   learned.

   The other node's Route Cache SHOULD support storing more than one route Caches) in response to each
   destination.  In searching the this
   Route Cache for Request does not contain a route to some
   destination node, that assumes the Route Cache is indexed by destination node
   address.  The following properties describe existence of
   this searching function
   on broken link.

4. Conceptual Data Structures

   This document describes the operation of the DSR protocol in terms
   of a Route Cache:

    -  Each number of conceptual data structures.  This section describes
   each of these data structures and provides an overview of its use
   in the protocol.  In an implementation of DSR at any node the protocol, these data
   structures MAY choose be implemented in any appropriate
       strategy and algorithm for searching its manner consistent with the
   external behavior described in this document.

4.1. Route Cache and
       selecting

   All ad hoc network routing information needed by a "best" route node implementing
   DSR is stored in that node's Route Cache.  Each node in the network
   maintains its own Route Cache.  A node adds information to its
   Route Cache as it learns of new links between nodes in the destination from among those
       found.  For ad hoc
   network; for example, a node MAY choose to select the shortest
       route to the destination (the shortest sequence may learn of hops), or new links when it
       MAY use an alternate metric to select the route receives
   a packet carrying a Route Request, Route Reply, or DSR source route.
   Likewise, a node removes information from its Route Cache as it
   learns that existing links in the Cache.

    -  However, if there are multiple cached routes to ad hoc network have broken; for
   example, a destination,
       the selection node may learn of routes a broken link when searching the it receives a packet
   carrying a Route Cache SHOULD
       prefer routes that do not have Error or through the External flag set on any node.
       This preference will select routes that lead directly link-layer retransmission
   mechanism reporting a failure in forwarding a packet to its next-hop
   destination.

   Anytime a node adds new information to its Route Cache, the
       target node over routes that attempt
   SHOULD check each packet in its own Send Buffer (Section 4.2) to reach
   determine whether a route to that packet's IP Destination Address
   now exists in the target via any
       external networks connected node's Route Cache (including the information just
   added to the DSR ad hoc network.

    -  In addition, any route selected when searching the Route Cache
       MUST NOT have the External bit set for any nodes other than
       possibly the first node, the last node, or both; Cache).  If so, the External bit
       MUST NOT packet SHOULD then be set for any intermediate hops in the sent using
   that route selected.

   An implementation of a Route Cache MAY provide and removed from the Send Buffer.

   It is possible to interface a fixed capacity DSR network with other networks,
   external to this DSR network.  Such external networks may, for
   example, be the cache, Internet, or the cache size MAY may be variable. other ad hoc networks routed
   with a routing protocol other than DSR.  Such external networks may
   also be other DSR networks that are treated as external networks
   in order to improve scalability.  The following
   properties describe complete handling of such
   external networks is beyond the management scope of available space within this document.  However,
   this document specifies a node's
   Route Cache:

    -  Each implementation minimal set of DSR at each node MAY choose any
       appropriate policy for managing requirements and features
   necessary to allow nodes only implementing this specification to
   interoperate correctly with nodes implementing interfaces to such
   external networks.  This minimal set of requirements and features
   involve the entries First Hop External (F) and Last Hop External (L)
   bits in its a DSR Source Route Cache,
       such as when limited cache capacity requires option (Section 5.7) and a choice of which
       entries to retain Route Reply
   option (Section 5.3) in the Cache.  For example, a node MAY chose a
       "least recently used" (LRU) cache replacement policy, packet's DSR header (Section 5).  These
   requirements also include the addition of an External flag bit
   tagging each link in which the entry last used longest ago is discarded Route Cache, copied from the cache if a
       decision needs to be made to allow space First Hop
   External (F) and Last Hop External (L) bits in the cache DSR Source Route
   option or Route Reply option from which this link was learned.

   The Route Cache SHOULD support storing more than one route to each
   destination.  In searching the Route Cache for a route to some
       new entry being added.

    -  However,
   destination node, the Route Cache replacement policy SHOULD allow routes
       to be categorized based upon "preference", where routes with is indexed by destination node
   address.  The following properties describe this searching function
   on a
       higher preferences are less likely Route Cache:

    -  Each implementation of DSR at any node MAY choose any appropriate
       strategy and algorithm for searching its Route Cache and
       selecting a "best" route to be removed from the cache. destination from among those
       found.  For example, a node could prefer routes for which MAY choose to select the shortest
       route to the destination (the shortest sequence of hops), or it initiated
       MAY use an alternate metric to select the route from the Cache.

    -  However, if there are multiple cached routes to a destination,
       the selection of routes when searching the Route Discovery over Cache MUST
       prefer routes that it learned as do not have the result of
       promiscuous snooping External flag set on other packets.  In particular, a any link.
       This preference will select routes that lead directly to the
       target node
       SHOULD prefer over routes that it attempt to reach the target via any
       external networks connected to the DSR ad hoc network.

    -  In addition, any route selected when searching the Route Cache
       MUST NOT have the External bit set for any links other than
       possibly the first link, the last link, or both; the External bit
       MUST NOT be set for any intermediate hops in the route selected.

   An implementation of a Route Cache MAY provide a fixed capacity
   for the cache, or the cache size MAY be variable.  The following
   properties describe the management of available space within a node's
   Route Cache:

    -  Each implementation of DSR at each node MAY choose any
       appropriate policy for managing the entries in its Route Cache,
       such as when limited cache capacity requires a choice of which
       entries to retain in the Cache.  For example, a node MAY chose a
       "least recently used" (LRU) cache replacement policy, in which
       the entry last used longest ago is discarded from the cache if a
       decision needs to be made to allow space in the cache for some
       new entry being added.

    -  However, the Route Cache replacement policy SHOULD allow routes
       to be categorized based upon "preference", where routes with a
       higher preferences are less likely to be removed from the cache.
       For example, a node could prefer routes for which it initiated
       a Route Discovery over routes that it learned as the result of
       promiscuous snooping on other packets.  In particular, a node
       SHOULD prefer routes that it is presently using over those that
       it is not.

   Any suitable data structure organization, consistent with this
   specification, MAY be used to implement the Route Cache in any node.
   For example, the following two types of organization are possible:

    -  In DSR, the route returned in each Route Reply that is received
       by the initiator of a Route Discovery (or that is learned from
       the header of overhead packets, as described in Section 6.1.4)
       represents a complete path (a sequence of links) leading to the
       destination node.  By caching each of these paths separately,
       a "path cache" organization for the Route Cache can be formed.
       A path cache is very simple to implement and easily guarantees
       that all routes are loop-free, since each individual route from
       a Route Reply or Route Request or used in a packet is loop-free.
       To search for a route in a path cache data structure, the sending
       node can simply search its Route Cache for any path (or prefix of
       a path) that leads to the intended destination node.

       This type of organization for the Route Cache in DSR has been
       extensively studied through simulation [5, 11, 18] 9, 12, 19] and
       through implementation of DSR in a mobile outdoor testbed under
       significant workload [19, 20, 20]. [20, 21, 22].

    -  Alternatively, a "link cache" organization could be used for the
       Route Cache, in which each individual link (hop) in the routes
       returned in Route Reply packets (or otherwise learned from the
       header of overhead packets) is added to a unified graph data
       structure of this node's current view of the network topology.
       To search for a route in link cache, the sending node must use
       a more complex graph search algorithm, such as the well-known
       Dijkstra's shortest-path algorithm, to find the current best path
       through the graph to the destination node.  Such an algorithm is
       more difficult to implement and may require significantly more
       CPU time to execute.

       However, a link cache organization is more powerful than a path
       cache organization, in its ability to effectively utilize all of
       the potential information that a node might learn about the state
       of the network: network.  In particular, links learned from different
       Route Discoveries or from the header of any overheard packets can
       be merged together to form new routes in the network, but this
       is not possible in a path cache due to the separation of each
       individual path in the cache.

       This type of organization for the Route Cache in DSR, including
       the effect of a range of implementation choices, has been studied
       through detailed simulation [9].

   The choice of data structure organization to use for the Route Cache
   in any DSR implementation is a local matter for each node and affects
   only performance; any reasonable choice of organization for the Route
   Cache does not affect either correctness or interoperability.

4.2. Route Request Table

   The Route Request Table records information about

   Each entry in the Route Requests that Cache SHOULD have been recently originated or forwarded by this node.  The table
   is indexed by IP address.

   The Route Request Table on a node records the following information
   about nodes timeout associated
   with it, to which this node has initiated a Route Request:

    -  The time that this node last originated a Route Request for allow that
       target node.

    -  The number of consecutive Route Requests initiated for this
       target since receiving a valid Route Reply giving a route entry to that
       target node.

    -  The remaining amount of time before which this node MAY next
       attempt at a Route Discovery for that target node.

    -  The Time-to-Live (TTL) field be deleted if not used in the IP header of last Route
       Request initiated by this node for that target node.

   In addition, the Route Request Table on a node also records the
   following information about initiator nodes from which this node has
   received a Route Request:

    -  A FIFO cache within some
   time.  The particular choice of size REQUEST_TABLE_IDS entries containing the
       Identification value algorithm and target address from data structure used
   to implement the most recent Route Requests received by this node from that initiator node.

   Nodes Cache SHOULD use an LRU policy to manage be considered in choosing the
   timeout for entries in their the Route
   Request Table. Cache.  The number of Identification values to retain configuration variable
   RouteCacheTimeout defined in each Route Request
   Table entry, REQUEST_TABLE_IDS, MUST NOT Section 7 specifies the timeout to be unlimited, since,
   applied to entries in the worst case, when a node crashes and reboots, the first
   REQUEST_TABLE_IDS Route Discoveries Cache, although it initiates after rebooting
   could appear to be duplicates is also possible
   to instead use an adaptive policy in choosing timeout values rather
   than using a single timeout setting for all entries; for example, the
   Link-MaxLife cache design (below) uses an adaptive timeout algorithm
   and does not use the RouteCacheTimeout configuration variable.

   As guidance to implementors, Appendix A describes a type of link
   cache known as "Link-MaxLife" that has been shown to outperform
   other nodes types of link caches and path caches studied in detailed
   simulation [9].  Link-MaxLife is an adaptive link cache in which each
   link in the network.
   In addition, cache has a timeout that is determined dynamically by the
   caching node SHOULD base according to its initial Identification value,
   used observed past behavior of the two nodes
   at the ends of the link; in addition, when selecting a route for Route Discoveries after rebooting, on a battery backed-up
   clock or other persistent memory device, in order
   packet being sent to help avoid some destination, among cached routes of equal
   length (number of hops) to that destination, Link-MaxLife selects the
   route with the longest expected lifetime (highest minimum timeout of
   any
   possible such delay link in successfully discovering new routes after
   rebooting; if no such source the route).  Use of initial Identification value the Link-MaxLife design for the Route
   Cache is
   available, a node SHOULD base its initial Identification value after
   rebooting on a random number.

4.3. recommended in implementations of DSR.

4.2. Send Buffer

   The Send Buffer of a node implementing DSR is a queue of packets that
   cannot be sent by that node because it does not yet have a source
   route to each such packet's destination.  Each packet in the Send
   Buffer is logically associated with the time that it was placed into
   the Buffer, and SHOULD be removed from the Send Buffer and silently
   discarded SEND_BUFFER_TIMEOUT seconds after a period of SendBufferTimeout after initially being
   placed in the Buffer.  If necessary, a FIFO strategy SHOULD be used
   to evict packets before they timeout to prevent the buffer from
   overflowing.

   Subject to the rate limiting defined in Section 6.2, a Route
   Discovery SHOULD be initiated as often as possible for the
   destination address of any packets residing in the Send Buffer.

4.4. Retransmission Buffer

4.3. Route Request Table

   The Retransmission Buffer Route Request Table of a node implementing DSR is a queue
   of packets sent records
   information about Route Requests that have been recently originated
   or forwarded by this node.  The table is indexed by IP address.

   The Route Request Table on a node that are awaiting records the receipt following information
   about nodes to which this node has initiated a Route Request:

    -  The Time-to-Live (TTL) field used in the IP header of an
   acknowledgment from the next hop in Route
       Request for the source route (Section 5.7).
   For each packet in last Route Discovery initiated by this node for
       that target node.  This value allows the Retransmission Buffer, a node maintains (1) to implement a
   count
       variety of algorithms for controlling the number spread of retransmissions and (2) the time its Route
       Request on each Route Discovery initiated for a target.  As
       examples, two possible algorithms for this use of the last
   retransmission.

   Packets TTL field
       are removed from the Retransmission Buffer when an
   acknowledgment is received or when the described in Section 3.3.4.

    -  The time that this node last originated a Route Request for that
       target node.

    -  The number of retransmissions
   exceeds DSR_MAXRXTSHIFT.  In the later case, the removal of the
   packet from the Retransmission Buffer SHOULD result in consecutive Route Discoveries initiated for this
       target since receiving a valid Route Error
   being returned Reply giving a route to the original source of the packet (Section 6.3).

5. DSR Header Format that
       target node.

    -  The Dynamic Source Routing protocol makes use remaining amount of time before which this node MAY next
       attempt at a special header
   carrying control information Route Discovery for that can be included in any existing IP
   packet.  This DSR header in a packet contains a small fixed-sized,
   4-octet portion, followed by target node.  When the
       node initiates a sequence of zero or more DSR options
   carrying optional information.  The end of new Route Discovery for this target node, this
       field in the sequence of DSR
   options in the DSR header is implied by total length of the DSR
   header.

   The DSR header Route Request Table entry for that target node is inserted in
       initialized to the packet following timeout for that Route Discovery, after which
       the packet's IP
   header, before any following header such as node MAY initiate a traditional (e.g., TCP
   or UDP) transport layer header.  Specifically, the Protocol field
   in the IP header is used to indicate new Discovery for that target.  Until
       a DSR header follows the
   IP header, and valid Route Reply is received for this target node address,
       a node MUST implement a back-off algorithm in determining this
       timeout value for each successive Route Discovery initiated
       for this target using the Next Header field same Time-to-Live (TTL) value in the DSR
       IP header is used to
   indicate the type of protocol header (such as a transport layer
   header) following the DSR header. Route Request packet.  The total length of timeout between
       such consecutive Route Discovery initiations SHOULD increase by
       doubling the DSR header (and thus timeout value on each new initiation.

   In addition, the total, combined
   length of all DSR options present) MUST be Route Request Table on a multiple of 4 octets.
   This requirement preserves node also records the alignment of any
   following headers in
   the packet.

5.1. Fixed Portion of DSR Header

   The fixed portion of the DSR header is used to carry information that
   must be present in any DSR header.  This fixed portion of the DSR
   header about initiator nodes from which this node has
   received a Route Request:

    -  A FIFO cache of size RequestTableIds entries containing the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  |    Reserved   |        Payload Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                            Options                            .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header

         8-bit selector.  Identifies the type of header immediately
         following the DSR header.  Uses the same values as the IPv4
         Protocol field [26].

      Reserved

         Sent as 0; ignored on reception.

      Payload Length

         The length of the DSR header, excluding the 4-octet fixed
         portion.  The
       Identification value of the Payload Length field defines the
         total length of all options carried in the DSR header.

      Options

         Variable-length field; the length of and target address from the Options field is
         specified most recent
       Route Requests received by the Payload Length field in this DSR header.
         Contains one or more pieces of optional information (DSR
         options), encoded in type-length-value (TLV) format (with the
         exception of node from that initiator node.

   Nodes SHOULD use an LRU policy to manage the Pad1 option, described entries in Section 5.8). their Route
   Request Table.

   The placement of DSR options following the fixed portion number of the DSR
   header MAY be padded for alignment.  However, due Identification values to the typically
   limited available wireless bandwidth retain in ad hoc networks, this padding
   is not required, and receiving nodes each Route
   Request Table entry, RequestTableIds, MUST NOT expect options within
   a DSR header to be aligned.  A node inserting a DSR header into
   a packet MUST set the Don't Fragment (DF) bit unlimited, since,
   in the packet's IP
   header.

   The worst case, when a node crashes and reboots, the first
   RequestTableIds Route Discoveries it initiates after rebooting
   could appear to be duplicates to the other nodes in the network.
   In addition, a node SHOULD base its initial Identification value,
   used for Route Discoveries after rebooting, on a battery backed-up
   clock or other persistent memory device, in order to help avoid
   any possible such delay in successfully discovering new routes
   after rebooting; if no such source of initial Identification
   value is available, a node after rebooting SHOULD base its initial
   Identification value on a random number.

4.4. Gratuitous Route Reply Table

   The Gratuitous Route Reply Table of a node implementing DSR records
   information about "gratuitous" Route Replies sent by this node as
   part of automatic route shortening.  As described in Section 3.4.3,
   a node returns a gratuitous Route Reply when it overhears a packet
   transmitted by some node, for which the node overhearing the
   packet was not the intended next-hop node but was named later in
   the unexpended hops of the source route in that packet; the node
   overhearing the packet returns a gratuitous Route Reply to the
   original sender of the packet, listing the shorter route (not
   including the hops of the source route "skipped over" by this
   packet).  A node uses its Gratuitous Route Reply Table to limit the
   rate at which it originates gratuitous Route Replies to the same
   original sender for the same node from which it overheard a packet to
   trigger the gratuitous Route Reply.

   Each entry in the Gratuitous Route Reply Table of a node contains the
   following types fields:

    -  The address of the node to which this node originated a
       gratuitous Route Reply.

    -  The address of the node from which this node overheard the packet
       triggering that gratuitous Route Reply.

    -  The remaining time before which this entry in the Gratuitous
       Route Reply Table expires and SHOULD be deleted by the node.
       When a node creates a new entry in its Gratuitous Route Reply
       Table, the timeout value for that entry should be initialized to
       the value GratReplyHoldoff.

   When a node overhears a packet that would trigger a gratuitous
   Route Reply, if a corresponding entry already exists in the node's
   Gratuitous Route Reply Table, then the node SHOULD NOT send a
   gratuitous Route Reply for that packet.  Otherwise (no corresponding
   entry already exists), the node SHOULD create a new entry in its
   Gratuitous Route Reply Table to record that gratuitous Route Reply,
   with a timeout value of GratReplyHoldoff.

4.5. Network Interface Queue and Retransmission Buffer

   Depending on factors such as the structure and organization of
   the operating system, protocol stack implementation, network
   interface device driver, and network interface hardware, a
   packet being transmitted could be queued in a variety of ways.
   For example, outgoing packets from the network protocol stack
   might be queued at the operating system or link layer, before
   transmission by the network interface.  The network interface
   might also provide a retransmission mechanism for packets, such
   as occurs in IEEE 802.11 [11]; the DSR protocol also requires
   limited retransmission of packets as part of Route Maintenance.  The
   operation of DSR is defined here in terms of two conceptual data
   structures that together incorporate this queueing and retransmission
   behavior.

   The Network Interface Queue of a node implementing DSR is an output
   queue of packets from the network protocol stack waiting to be
   transmitted by the network interface; for example, in the 4.4BSD
   Unix network protocol stack implementation, this queue for a network
   interface is represented as a "struct ifqueue" [33].  This queue is
   used to hold packets while the network interface is in the process of
   transmitting another packet.

   The Retransmission Buffer of a node implementing DSR is a queue of
   packets sent by this node that are awaiting retransmission as part
   of Route Maintenance.  For each packet in the Retransmission Buffer,
   a node maintains a count of the number of retransmissions and the
   time of the last retransmission.  The Retransmission Buffer MAY be
   of limited size; when adding a new packet to the Retransmission
   Buffer, if the buffer size is insufficient to hold the new packet,
   the new packet SHOULD be silently discarded.  The maximum number of
   retransmission attempts for a packet for Route Maintenance (after the
   initial transmission of the packet) is MaxMaintRexmt.  After this
   time, if Route Maintenance for a packet has not been satisfied, the
   packet SHOULD be removed from the Retransmission Buffer, stopping
   retransmissions for that packet; in this case, the node also SHOULD
   originate a Route Error for this packet to the original source of the
   packet (Section 6.3) and SHOULD salvage the packet (Section 6.3.6) if
   it has another route to the packet's IP Destination Address in its
   Route Cache.  The definition of MaxMaintRexmt conceptually includes
   any retransmissions that might be attempted for a packet at the link
   layer or within the network interface hardware.  The retransmission
   timeout value to use for each transmission attempt for a packet
   depends on the type of acknowledgement mechanism used for Route
   Maintenance for that attempt, as described in Section 6.3.

5. DSR Header Format

   The Dynamic Source Routing protocol makes use of a special header
   carrying control information that can be included in any existing IP
   packet.  This DSR header in a packet contains a small fixed-sized,
   4-octet portion, followed by a sequence of zero or more DSR options
   carrying optional information.  The end of the sequence of DSR
   options in the DSR header is implied by total length of the DSR
   header.

   For IPv4, the DSR header MUST immediately follow the IP header in the
   packet.  (If a Hop-by-Hop Options extension header, as defined in
   IPv6 [6], becomes defined for IPv4, the DSR header MUST immediately
   follow the Hop-by-Hop Options extension header, if one is present in
   the packet, and MUST otherwise immediately follow the IP header.)

   To add a DSR header to a packet, the DSR header is inserted following
   the packet's IP header, before any following header such as a
   traditional (e.g., TCP or UDP) transport layer header.  Specifically,
   the Protocol field in the IP header is used to indicate that a DSR
   header follows the IP header, and the Next Header field in the DSR
   header is used to indicate the type of protocol header (such as a
   transport layer header) following the DSR header.

   If any headers follow the DSR header in a packet, the total length
   of the DSR header (and thus the total, combined length of all DSR
   options present) MUST be a multiple of 4 octets.  This requirement
   preserves the alignment of these following headers in the packet.

5.1. Fixed Portion of DSR Header

   The fixed portion of the DSR header is used to carry information that
   must be present in any DSR header.  This fixed portion of the DSR
   header has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  |    Reserved   |        Payload Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                            Options                            .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header

         8-bit selector.  Identifies the type of header immediately
         following the DSR header.  Uses the same values as the IPv4
         Protocol field [29].

      Reserved

         MUST be sent as 0 and ignored on reception.

      Payload Length

         The length of the DSR header, excluding the 4-octet fixed
         portion.  The value of the Payload Length field defines the
         total length of all options carried in the DSR header.

      Options

         Variable-length field; the length of the Options field is
         specified by the Payload Length field in this DSR header.
         Contains one or more pieces of optional information (DSR
         options), encoded in type-length-value (TLV) format (with the
         exception of the Pad1 option, described in Section 5.8).

   The placement of DSR options following the fixed portion of the DSR
   header MAY be padded for alignment.  However, due to the typically
   limited available wireless bandwidth in ad hoc networks, this padding
   is not required, and receiving nodes MUST NOT expect options within a
   DSR header to be aligned.

   A node inserting a DSR header into a packet MUST set the Don't
   Fragment (DF) bit in the packet's IP header.

   The following types of DSR options are defined in this document for
   use within a DSR header:

    -  Route Request option (Section 5.2)

    -  Route Reply option (Section 5.3)

    -  Route Error option (Section 5.4)

    -  Acknowledgement Request option (Section 5.5)

    -  Acknowledgement option (Section 5.6)

    -  DSR Source Route option (Section 5.7)

    -  Pad1 option (Section 5.8)

    -  PadN option (Section 5.9)

5.2. Route Request Option

   The Route Request option in a DSR header is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Target Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IP fields:

      Source Address

         MUST be set to the address of the node originating this packet.
         Intermediate nodes that retransmit the packet to propagate the
         Route Request MUST NOT change this field.

      Destination Address

         MUST be set to the IP limited broadcast address
         (255.255.255.255).

      Hop Limit (TTL)

         MAY be varied from 1 to 255, for example to implement
         non-propagating Route Requests and Route Request expanding-ring
         searches (Section 3.3.4).

   Route Request fields:

      Option Type

         2

      Opt Data Len

         8-bit unsigned integer.  Length of the option, in octets,
         excluding the Option Type and Opt Data Len fields.

      Identification

         A unique value generated by the initiator (original sender) of
         the Route Request.  Nodes initiating a Route Request generate
         a new Identification value for each Route Request, for example
         based on a sequence number counter of all Route Requests
         initiated by the node.

         This value allows a receiving node to determine whether it
         has recently seen a copy of this Route Request:  if this
         Identification value is found by this receiving node in its
         Route Request Table (in the cache of Identification values
         in the entry there for this initiating node), this receiving
         node MUST discard the Route Request.  When propagating a Route
         Request, this field MUST be copied from the received copy of
         the Route Request being propagated.

      Target Address

         The address of the node that is the target of the Route
         Request.

      Address[1..n]

         Address[i] is the address of the i-th node recorded in the
         Route Request option.  The address given in the Source Address
         field in the IP header is the address of the initiator of
         the Route Discovery and MUST NOT be listed in the Address[i]
         fields; the address given in Address[1] is thus the address
         of the first node on the path after the initiator.  The
         number of addresses present in this field is indicated by the
         Opt Data Len field in the option (n = (Opt Data Len - 6) / 4).
         Each node propagating the Route Request adds its own address to
         this list, increasing the Opt Data Len value by 4 octets.

   The Route Request option MUST NOT appear more than once within a DSR
   header.

5.3. Route Reply Option

   The Route Reply option in a DSR header is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |  Option Type  |  Opt Data Len |L|   Reserved  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IP fields:

      Source Address

         Set to the address of the node sending the Route Reply.
         In the case of a node sending a reply from its Route
         Cache (Section 3.3.2) or sending a gratuitous Route Reply
         (Section 3.4.3), this address can differ from the address that
         was the target of the Route Discovery.

      Destination Address

         MUST be set to the address of the source node of the route
         being returned.  Copied from the Source Address field of the
         Route Request generating the Route Reply, or in the case of a
         gratuitous Route Reply, copied from the Source Address field of
         the data packet triggering the gratuitous Reply.

   Route Reply fields:

      Option Type

         3

      Opt Data Len

         8-bit unsigned integer.  Length of the option, in octets,
         excluding the Option Type and Opt Data Len fields.

      Last Hop External (L)

         Set to indicate that the last hop given by the Route Reply
         (the link from Address[n-1] to Address[n]) is actually an
         arbitrary path in a network external to the DSR network; the
         exact route outside the DSR network is not represented in the
         Route Reply.  Nodes caching this hop in their Route Cache MUST
         flag the cached hop with the External flag.  Such hops MUST NOT
         be returned in a cached Route Reply generated from this Route
         Cache entry, and selection of routes from the Route Cache to
         route a packet being sent MUST prefer routes that contain no
         hops flagged as External.

      Reserved

         MUST be sent as 0 and ignored on reception.

      Address[1..n]

         The source route being returned by the Route Reply.  The route
         indicates a sequence of hops, originating at the source node
         specified in the Destination Address field of the IP header
         of the packet carrying the Route Reply, through each of the
         Address[i] nodes in the order listed in the Route Reply,
         ending with the destination node indicated by Address[n].
         The number of addresses present in the Address[1..n]
         field is indicated by the Opt Data Len field in the option
         (n = (Opt Data Len - 1) / 4).

   A Route Reply option MAY appear one or more times within a DSR
   header.

5.4. Route Error Option

   The Route Error option in a DSR header is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |   Error Type  |Reservd|Salvage|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Error Source Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Error Destination Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                   Type-Specific Information                   .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         4

      Opt Data Len

         8-bit unsigned integer.  Length of the option, in octets,
         excluding the Option Type and Opt Data Len fields.

         For the current definition of the Route Error option,
         this field MUST be set to 10, plus the size of any
         Type-Specific Information present in the Route Error.  Further
         extensions to the Route Error option format may also be
         included after the Type-Specific Information portion of the
         Route Error option specified above.  The presence of such
         extensions will be indicated by the Opt Data Len field.
         When the Opt Data Len is greater than that required for
         the fixed portion of the Route Error plus the necessary
         Type-Specific Information as indicated by the Option Type
         value in the option, the remaining octets are interpreted as
         extensions.  Currently, no such further extensions have been
         defined.

      Error Type

         The type of error encountered.  Currently, the following type
         value is defined:

             1 = NODE_UNREACHABLE

         Other values of the Error Type field are reserved for future
         use.

      Reservd

         Reserved.  MUST be sent as 0 and ignored on reception.

      Salvage

         A 4-bit unsigned integer.  Copied from the Salvage field in
         the DSR Source Route option of the packet triggering the Route
         Error.

         The "total salvage count" of the Route Error option is derived
         from the value in the Salvage field of this Route Error option
         and all preceding Route Error options in the packet as follows:
         the total salvage count is the sum of, for each such Route
         Error option, one plus the value in the Salvage field of that
         Route Error option.

      Error Source Address

         The address of the node originating the Route Error (e.g., the
         node that attempted to forward a packet and discovered the link
         failure).

      Error Destination Address

         The address of the node to which the Route Error must be
         delivered For example, when the Error Type field is set to
         NODE_UNREACHABLE, this field will be set to the address of the
         node that generated the routing information claiming that the
         hop from the Error Source Address to Unreachable Node Address
         (specified in the Type-Specific Information) was a valid hop.

      Type-Specific Information

         Information specific to the Error Type of this Route Error
         message.

   Currently, the Type-Specific Information field is defined only for
   Route Error messages of type NODE_UNREACHABLE.  In this case, the
   Type-Specific Information field is defined as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Unreachable Node Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      Unreachable Node Address

         The address of the node that was found to be unreachable
         (the next-hop neighbor to which the node with address
         Error Source Address was attempting to transmit the packet).

   A Route Error option MAY appear one or more times within a DSR
   header.

5.5. Acknowledgment Request Option

   The Acknowledgment Request option in a DSR header is encoded as
   follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         5

      Opt Data Len

         8-bit unsigned integer.  Length of the option, in octets,
         excluding the Option Type and Opt Data Len fields.

      Identification

         The Identification field is set to a unique value and is copied
         into the Identification field of the Acknowledgement option
         when returned by the node receiving the packet over this hop.

   An Acknowledgement Request option MUST NOT appear more than once
   within a DSR header.

5.6. Acknowledgment Option

   The Acknowledgment option in a DSR header is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       ACK Source Address                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     ACK Destination Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         6

      Opt Data Len

         8-bit unsigned integer.  Length of the option, in octets,
         excluding the Option Type and Opt Data Len fields.

      Identification

         Copied from the Identification field of the Acknowledgement
         Request option of the packet being acknowledged.

      ACK Source Address

         The address of the node originating the acknowledgment.

      ACK Destination Address

         The address of the node to which the acknowledgment is to be
         delivered.

   An Acknowledgement option MAY appear one or more times within a DSR
   header.

5.7. DSR Source Route Option

   The DSR Source Route option in a DSR header is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |F|L|Reservd|Salvage| Segs Left |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         7

      Opt Data Len

         8-bit unsigned integer.  Length of the option, in octets,
         excluding the Option Type and Opt Data Len fields.  For the
         format of the DSR Source Route option defined here, this field
         MUST be set to the value (n * 4) + 2, where n is the number of
         addresses present in the Address[i] fields.

      First Hop External (F)

         Set to indicate that the first hop indicated by the DSR
         Source Route option is actually an arbitrary path in a network
         external to the DSR network; the exact route outside the DSR
         network is not represented in the DSR Source Route option.
         Nodes caching this hop in their Route Cache MUST flag the
         cached hop with the External flag.  Such hops MUST NOT be
         returned in a Route Reply generated from this Route Cache
         entry, and selection of routes from the Route Cache to route
         a packet being sent MUST prefer routes that contain no hops
         flagged as External.

      Last Hop External (L)

         Set to indicate that the last hop indicated by the DSR Source
         Route option is actually an arbitrary path in a network
         external to the DSR network; the exact route outside the DSR
         network is not represented in the DSR Source Route option.
         Nodes caching this hop in their Route Cache MUST flag the
         cached hop with the External flag.  Such hops MUST NOT be
         returned in a Route Reply generated from this Route Cache
         entry, and selection of routes from the Route Cache to route
         a packet being sent MUST prefer routes that contain no hops
         flagged as External.

      Reserved

         MUST be sent as 0 and ignored on reception.

      Salvage

         A 4-bit unsigned integer.  Count of number of times that
         this packet has been salvaged as a part of DSR routing
         (Section 3.4.1).

      Segments Left (Segs Left)

         Number of route segments remaining, i.e., number of explicitly
         listed intermediate nodes still to be visited before reaching
         the final destination.

      Address[1..n]

         The sequence of addresses of the source route.  In routing
         and forwarding the packet, the source route is processed as
         described in Sections 6.1.3 and 6.1.5.  The number of addresses
         present in the Address[1..n] field is indicated by the
         Opt Data Len field in the option (n = (Opt Data Len - 2) / 4).

   When forwarding a packet along a DSR source route using a DSR Source
   Route option in the packet's DSR header, the Destination Address
   field in the packet's IP header is always set to the address of the
   packet's ultimate destination.  A node receiving a packet containing
   a DSR header with a DSR Source Route option MUST examine the
   indicated source route to determine if it is the intended next-hop
   node for the packet and determine how to forward the packet, as
   defined in Sections 6.1.4 and 6.1.5.

5.8. Pad1 Option

   The Pad1 option in a DSR header is encoded as follows:

   +-+-+-+-+-+-+-+-+
   |  Option Type  |
   +-+-+-+-+-+-+-+-+

      Option Type

         0

   A Pad1 option MAY be included in the Options field of a DSR header
   in order to align subsequent DSR options, but such alignment is
   not required and MUST NOT be expected by a node receiving a packet
   containing a DSR header.

   If any headers follow the DSR header in a packet, the total length of
   a DSR header, indicated by the Payload Length field in the DSR header
   MUST be a multiple of 4 octets.  In this case, when building a DSR
   header in a packet, sufficient Pad1 or PadN options MUST be included
   in the Options field of the DSR header to make the total length a
   multiple of 4 octets.

   If more than one consecutive octet of padding is being inserted in
   the Options field of a DSR header, the PadN option, described next,
   SHOULD be used, rather than multiple Pad1 options.

   Note that the format of the Pad1 option is a special case; it does
   not have an Opt Data Len or Option Data field.

5.9. PadN Option

   The PadN option in a DSR header is encoded as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
   |  Option Type  |  Opt Data Len |   Option Data
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

      Option Type

         1

      Opt Data Len

         8-bit unsigned integer.  Length of the option, in octets,
         excluding the Option Type and Opt Data Len fields.

      Option Data

         A number of zero-valued octets equal to the Opt Data Len.

   A PadN option MAY be included in the Options field of a DSR header
   in order to align subsequent DSR options, but such alignment is
   not required and MUST NOT be expected by a node receiving a packet
   containing a DSR header.

   If any headers follow the DSR header in a packet, the total length of
   a DSR header, indicated by the Payload Length field in the DSR header
   MUST be a multiple of 4 octets.  In this case, when building a DSR
   header in a packet, sufficient Pad1 or PadN options MUST be included
   in the Options field of the DSR header to make the total length a
   multiple of 4 octets.

6. Detailed Operation

6.1. General Packet Processing

6.1.1. Originating a Packet

   When originating any packet, a node using DSR routing MUST perform
   the following sequence of steps:

    -  Search the node's Route Cache for a route to the address given in
       the IP Destination Address field in the packet's header.

    -  If no such route is found in the Route Cache, then perform
       Route Discovery for the Destination Address, as described in
       Section 6.2.  Initiating a Route Discovery for this target node
       address results in the node adding a Route Request option in
       a DSR header in this existing packet, or saving this existing
       packet to its Send Buffer and initiating the Route Discovery
       by sending a separate packet containing such a Route Request
       option.  If the node chooses to initiate the Route Discovery
       by adding the Route Request option to this existing packet,
       it will replace the IP Destination Address field with the IP
       "limited broadcast" address (255.255.255.255) [3], copying the
       original IP Destination Address to the Target Address field of
       the new Route Request option added to the packet, as described in
       Section 6.2.1.

    -  If the packet now does not contain a Route Request option,
       then this node must have a route to the Destination Address
       of the packet; if the node has more than one route to this
       Destination Address, the node selects one to use for this packet.
       If the length of this route is greater than 1 hop, or if the
       node determines to request a DSR network-layer acknowledgement
       from the first-hop node in that route, then insert a DSR header
       into the packet, as described in Section 6.1.2, and insert a DSR
       Source Route option, as described in Section 6.1.3.  The source
       route in the packet is initialized from the selected route to the
       Destination Address of the packet.

    -  Transmit the packet to the first-hop node address given in
       selected source route, using Route Maintenance to retransmit the
       packet if necessary, as described in Section 6.3.

6.1.2. Adding a DSR Header to a Packet

   A node originating a packet adds a DSR header to the packet, if
   necessary, to carry information needed by the routing protocol.  A
   packet MUST NOT contain more than one DSR header.  A DSR header is
   added to a packet by performing the following sequence of steps
   (these steps assume that the packet contains no other headers that
   MUST be located in the packet before the DSR header):

    -  Insert a DSR header after the IP header but before any other
       header that may be present.

    -  Set the Next Header field of the DSR header to the Protocol
       number field of the packet's IP header.

    -  Set the Protocol field of the packet's IP header to the Protocol
       number assigned for a DSR header (TBA???).

6.1.3. Adding a DSR Source Route Option to a Packet

   A node originating a packet adds a DSR Source Route option to the
   packet, if necessary, in order to carry the source route from this
   originating node to the final destination address of the packet.
   Specifically, the node adding the DSR Source Route option constructs
   the DSR Source Route option and modifies the IP packet according to
   the following sequence of steps:

    -  The node creates a DSR Source Route option, as described in
       Section 5.7, and appends it to the DSR header in the packet.
       (A DSR header is added, as described in Section 6.1.2, if not
       already present.)

    -  The number of Address[i] fields to include in the DSR Source
       Route option (n) is the number of intermediate nodes in the
       source route for the packet (i.e., excluding address of the
       originating node and the final destination address of the
       packet).  The Segments Left field in the DSR Source Route option
       is initialized equal to n.

    -  The addresses within the source route for the packet are copied
       into sequential Address[i] fields in the DSR Source Route option,
       for i = 1, 2, ..., n.

    -  The First Hop External (F) bit in the DSR Source Route option is
       copied from the External bit flagging the first hop in the source
       route for the packet, as indicated in the Route Cache.

    -  The Last Hop External (L) bit in the DSR Source Route option is
       copied from the External bit flagging the last hop in the source
       route for the packet, as indicated in the Route Cache.

    -  The Salvage field in the DSR Source Route option is
       initialized to 0.

6.1.4. Processing a Received Packet

   When a node receives any packet (whether for forwarding, overheard,
   or as the final destination of the packet), if that packet contains a
   DSR header, then that node MUST process any options contained in that
   DSR header, in the order contained there.  Specifically:

    -  If the DSR header contains a Route Request option, the node
       SHOULD extract the source route from the Route Request and add
       this routing information to its Route Cache, subject to the
       conditions identified in Section 3.3.1.  The routing information
       from the Route Request is the sequence of hop addresses

          initiator, Address[1], Address[2], ..., Address[n]

       where initiator is the value of the Source Address field in
       the IP header of the packet carrying the Route Request (the
       address of the initiator of the Route Discovery), and each
       Address[i] is a node through which this Route Request has passed,
       in turn, during this Route Discovery.  The value n here is the
       number of addresses recorded in the Route Request option, or
       (Opt Data Len - 6) / 4.

       After possibly updating the node's Route Cache in response to
       the routing information in the Route Request option, the node
       MUST then process the Route Request option as described in
       Section 6.2.2.

    -  If the DSR header contains a Route Reply option, the node SHOULD
       extract the source route from the Route Reply and add this
       routing information to its Route Cache, subject to the conditions
       identified in Section 3.3.1.  The source route from the Route
       Reply is the sequence of hop addresses

          initiator, Address[1], Address[2], ..., Address[n]

       where initiator is the value of the Destination Address field in
       the IP header of the packet carrying the Route Reply (the address
       of the initiator of the Route Discovery), and each Address[i]
       is a node through which the source route passes, in turn, on
       the route to the target of the Route Discovery.  Address[n] is
       the address of the target.  If the Last Hop External (L) bit is
       set in the Route Reply, the node MUST flag the last hop from
       the Route Reply (the link from Address[n-1] to Address[n]) in
       its Route Cache as External.  The value n here is the number of
       addresses in the source route being returned in the Route Reply
       option, or (Opt Data Len - 1) / 4.

       After possibly updating the node's Route Cache in response to
       the routing information in the Route Reply option, then if the
       packet's IP Destination Address matches one of this node's IP
       addresses, the node MUST then process the Route Reply option as
       described in Section 6.2.5.

    -  If the DSR header contains a Route Error option, the node MUST
       process the Route Error option as described in Section 6.3.5.

    -  If the DSR header contains an Acknowledgement Request option, the
       node MUST process the Acknowledgement Request option as described
       in Section 6.3.3.

    -  If the DSR header contains an Acknowledgement option, then
       subject to the conditions identified in Section 3.3.1, the node
       SHOULD add to its Route Cache the single link from the node
       identified by the ACK Source Address field to the node identified
       by the ACK Destination Address field.

       After possibly updating the node's Route Cache in response to
       the routing information in the Acknowledgement option, the node
       MUST then process the Acknowledgement option as described in
       Section 6.3.3.

    -  If the DSR header contains a DSR Source Route option, the node
       SHOULD extract the source route from the DSR Source Route and
       add this routing information to its Route Cache, subject to the
       conditions identified in Section 3.3.1.  If the value of the
       Salvage field in the DSR Source Route option is zero, then the
       routing information from the DSR Source Route is the sequence of
       hop addresses

          source, Address[1], Address[2], ..., Address[n], destination

       and otherwise (Salvage is nonzero), the routing information from
       the DSR Source Route is the sequence of hop addresses

          Address[1], Address[2], ..., Address[n], destination

       where source is the value of the Source Address field in the IP
       header of the packet carrying the DSR Source Route option (the
       original sender of the packet), each Address[i] is the value in
       the Address[i] field in the DSR Source Route, and destination is
       the value of the Destination Address field in the packet's IP
       header (the last-hop address of the source route).  The value n
       here is the number of addresses in source route in the DSR Source
       Route option, or (Opt Data Len - 2) / 4.

       After possibly updating the node's Route Cache in response to
       the routing information in the DSR Source Route option, the node
       MUST then process the DSR Source Route option as described in
       Section 6.1.5.

    -  Any Pad1 or PadN options in the DSR header are ignored.

   Finally, if the Destination Address in the packet's IP header matches
   one of this receiving node's own IP address(es), remove the DSR
   header and all the included DSR options in the header, and pass the
   rest of the packet to the network layer.

6.1.5. Processing a Received DSR Source Route Option

   When a node receives a packet containing a DSR Source Route option
   (whether for forwarding, overheard, or as the final destination of
   the packet), that node SHOULD examine the packet to determine if
   the receipt of that packet indicates an opportunity for automatic
   route shortening, as described in Section 3.4.3.  Specifically, if
   this node is not the intended next-hop destination for the packet
   but is named in the later unexpended portion of the source route in
   the packet's DSR options Source Route option, then this packet indicates an
   opportunity for automatic route shortening:  the intermediate nodes
   after the node from which this node overheard the packet and before
   this node itself, are defined no longer necessary in the source route.  In
   this document for
   use within a DSR header:

    -  Route Request option (Section 5.2) case, this node SHOULD perform the following sequence of steps
   as part of automatic route shortening:

    -  The node searches its Gratuitous Route Reply option (Section 5.3)

    -  Route Error option (Section 5.4)

    -  Acknowledgement Request option (Section 5.5)

    -  Acknowledgement option (Section 5.6)

    -  Source Route option (Section 5.7)

    -  Pad1 option (Section 5.8)

    -  PadN option (Section 5.9)

5.2. Table for an entry
       describing a gratuitous Route Request Option

   The Reply earlier sent by this node,
       for which the original sender of the packet triggering the
       gratuitous Route Request DSR option is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Target Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IP fields:

      Source Address

         MUST be set Reply and the transmitting node from which this
       node overheard that packet in order to trigger the gratuitous
       Route Reply, both match the respective node addresses for this
       new received packet.  If such an entry is found in the address of node's
       Gratuitous Route Reply Table, the node originating SHOULD NOT perform
       automatic route shortening in response to this receipt of this
       packet.
         Intermediate nodes that retransmit

    -  Otherwise, the node creates an entry for this overheard packet to propagate the in
       its Gratuitous Route Request MUST NOT change Reply Table.  The timeout value for this field.

      Destination Address

         MUST new
       entry SHOULD be set initialized to the IP limited broadcast address
         (255.255.255.255).

      Hop Limit (TTL)

         MAY be varied value GratReplyHoldoff.  After
       this timeout has expired, the node SHOULD delete this entry from 1 to 255, for example to implement
         non-propagating
       its Gratuitous Route Requests and Reply Table.

    -  After creating the new Gratuitous Route Request expanding-ring
         searches (Section 3.3.4). Reply Table entry
       above, the node originates a gratuitous Route Request fields:

      Option Type

         2

      Opt Data Len

         8-bit unsigned integer.  Length of Reply to the option,
       IP Source Address of this overheard packet, as described in octets,
         excluding
       Section 3.4.3.

       If the Option Type and Opt Data Len fields.

      Identification

         A unique value generated by MAC protocol in use in the initiator (original sender) network is not capable of
         the Route Request.  Nodes initiating a
       transmitting unicast packets over uni-directional links, as
       discussed in Section 3.3.1, then in originating this Route Request generate Reply,
       the node MUST use a new Identification value source route for each routing the Route Request, for example
         based on a Reply
       packet that is obtained by reversing the sequence of hops over
       which the packet triggering the gratuitous Route Reply was routed
       in reaching and being overheard by this node; this reversing of
       the route uses the gratuitous Route Reply to test this sequence number counter
       of all hops for bi-directionality, preventing the gratuitous Route Requests
         initiated
       Reply from being received by the node.

         This value allows a receiving node to determine whether it
         has recently seen a copy initiator of this the Route Request:  if this
         Identification value Discovery
       unless each of the hops over which the gratuitous Route Reply is found by
       returned is bi-directional.

    -  Discard the overheard packet, since the packet has been received
       before its normal traversal of the packet's source route would
       have caused it to reach this receiving node.  Another copy of
       the packet will normally arrive at this node as indicated in its
         Route Request Table (in
       the cache packet's source route; discarding this initial copy of Identification values
         in the entry there for this initiating node),
       packet, which triggered the gratuitous Route Reply, will prevent
       the duplication of this receiving packet that would otherwise occur.

   If the packet is not discarded as part of automatic route shortening
   above, then the node MUST discard process the option according to the
   following sequence of steps:

    -  If the value of the Segments Left field in the DSR Source Route Request.  When propagating a
       option equals 0, then remove the DSR Source Route
         Request, this field MUST be copied option from the received copy
       DSR header.

    -  Else, let n equal (Opt Data Len - 2) / 4.  This is the number of
       addresses in the DSR Source Route Request being propagated.

      Target Address

         The address option.

    -  If the value of the node that Segments Left field is greater than n, then
       send an ICMP Parameter Problem, Code 0, message [26] to the IP
       Source Address, pointing to the Segments Left field, and discard
       the target of packet.  Do not process the DSR Source Route
         Request.

      Address[1..n]

         Address[i] is option further.

    -  Else, decrement the address value of the i-th hop recorded in the Route
         Request option.  The address given in the Source Address Segments Left field
         in the IP header by 1.  Let i
       equal n minus Segments Left.  This is the address of the initiator index of the Route
         Discovery and MUST NOT next
       address to be listed visited in the Address vector.

    -  If Address[i] fields; or the
         address given in Address[1] IP Destination Address is thus the address of a multicast
       address, then discard the first
         node on packet.  Do not process the path after DSR Source
       Route option further.

    -  If the initiator.  The number MTU of addresses
         present in this field is indicated by the Opt Data Len field in the option (n = (Opt Data Len - 2) / 4).  Each link over which this node propagating would transmit the Route Request adds its own address
       packet to this list, increasing
         the Opt Data Len value by 4 octets.

   The Route Request option MUST NOT appear more than once within a DSR
   header.

5.3. Route Reply Option

   The Route Reply DSR option is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                                   +-+-+-+-+-+-+-+-+
                                                   |  Option Type  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Opt Data Len |L|   Reserved  |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IP fields: forward it to the node Address[i] is less than the size
       of the packet, the node MUST discard the packet and send an ICMP
       Packet Too Big message to the packet's Source Address

         Set [26].

    -  Forward the packet to the IP address specified in the Address[i]
       field of the node sending IP header, following normal IP forwarding
       procedures, including checking and decrementing the Route Reply.
         In Time-to-Live
       (TTL) field in the case packet's IP header [27, 3].  In this
       forwarding of the packet, the next-hop node (identified by
       Address[i]) MUST be treated as a direct neighbor node:  the
       transmission to that next node sending MUST be done in a reply from its single IP
       forwarding hop, without Route
         Cache (Section 3.3.2) or sending a gratuitous Discovery and without searching the
       Route Reply
         (Section 3.4.2), this address can differ from Cache.

    -  In forwarding the address that
         was packet, perform Route Maintenance for the target next
       hop of the packet, by verifying that the packet was received by
       that next-hop node, as described in Section 6.3.

   Multicast addresses MUST NOT appear in a DSR Source Route Discovery. option or
   in the IP Destination Address

         MUST be set to the address field of a packet carrying a DSR Source
   Route option in a DSR header.

6.2. Route Discovery Processing

   Route Discovery is the source mechanism by which a node of the S wishing to send a
   packet to a destination node D obtains a source route
         being returned.  Copied from to D.  Route
   Discovery is used only when S attempts to send a packet to D and
   does not already know a route to D.  The node initiating a Route
   Discovery is known as the Source Address field "initiator" of the Route Request generating Discovery, and the
   destination node for which the Route Reply, or in Discovery is initiated is known
   as the case "target" of the Route Discovery.

   Route Discovery operates entirely on demand, with a
         gratuitous node initiating
   Route Reply, copied from the Source Address field Discovery based on its own origination of
         the data packet triggering the gratuitous Reply. new packets for
   some destination address to which it does not currently know a
   route.  Route Reply fields:

      Option Type

         3

      Opt Data Len

         8-bit unsigned integer.  Length Discovery does not depend on any periodic or background
   exchange of the option, routing information or neighbor node detection at any
   layer in octets,
         excluding the Option Type network protocol stack at any node.

   The Route Discovery procedure utilizes two types of messages, a Route
   Request (Section 5.2) and Opt Data Len fields.

      Last Hop External (L)

         Set to indicate that the last node indicated by the a Route Reply (Address[n]) is actually in a (Section 5.3), to actively
   search the ad hoc network external for a route to the desired destination.
   These DSR network; the exact sequence messages MAY be carried in any type of IP packet, through
   use of hops leading to it outside the DSR network is not represented header as described in the Route Reply.  Nodes
         caching this hop Section 5.

   Except as discussed in their Section 6.3.5, a Route Cache MUST flag the cached hop
         with the External flag.  Such hops MUST Discovery for a
   destination address SHOULD NOT be returned in a
         cached Route Reply generated from this Route Cache entry, and
         selection of routes from initiated unless the initiating
   node has a packet in its Send Buffer requiring delivery to that
   destination.  A Route Cache to route Discovery for a packet
         being sent SHOULD prefer routes that contain no hops flagged as
         External.

      Reserved

         Sent as 0; ignored on reception.

      Identification

         Copied from given target node MUST NOT be
   initiated unless permitted by the Identification field of rate-limiting information contained
   in the Route Request Table.  After each Route Discovery attempt, the
   interval between successive Route Discoveries for
         which this Reply is sent in response.  Sent as 0 if the target SHOULD
   be doubled, up to a maximum of MaxRequestPeriod, until a valid Route
   Reply is not sent in response to received for this target.

6.2.1. Originating a Route Request (a gratuitous

   A node initiating a Route Reply).

      Address[1..n]

         The source route being returned by the Discovery for some target creates and
   initializes a Route Reply.  The route
         indicates Request option in a sequence of hops, originating at DSR header in some IP packet.
   This MAY be a separate IP packet, used only to carry this Route
   Request option, or the source node
         specified MAY include the Route Request option
   in some existing packet that it needs to send to the Destination Address field of target node
   (e.g., the IP header
         of the packet carrying originated by this node, that caused the node to
   attempt Route Reply, through each Discovery for the destination address of the
         Address[i] nodes packet).
   The Route Request option MUST be included in the order listed a DSR header in the
   packet.  To initialize the Route Reply,
         ending with Request option, the destination node indicated by Address[n]. performs
   the following sequence of steps:

    -  The number Option Type in the option MUST be set to the value 2.

    -  The Opt Data Len field in the option MUST be set to the value 6.
       The total size of addresses present in the Address[1..n]
         field Route Request option when initiated
       is indicated by 8 octets; the Opt Data Len field in excludes the option
         (n = (Opt size of the
       Option Type and Opt Data Len fields themselves.

    - 3) / 4).

   A Route Reply  The Identification field in the option MUST be set to a new
       value, different from that used for other Route Requests recently
       initiated by this node for this same target address.  For
       example, each node MAY appear one or more times within maintain a DSR
   header.

5.4. single counter value for
       generating a new Identification value for each Route Error Option Request it
       initiates.

    -  The Route Error DSR Target Address field in the option MUST be set to the IP
       address that is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |   Error Type  |Reservd|Salvage|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Error the target of this Route Discovery.

   The Source Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Error Destination Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                   Type-Specific Information                   .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         4

      Opt Data Len

         8-bit unsigned integer.  Length in the IP header of this packet MUST be the option, node's
   own IP address.  The Destination Address in octets,
         excluding the Option Type and Opt Data Len fields.

         For the current definition IP header of this
   packet MUST be the IP "limited broadcast" address (255.255.255.255).

   A node MUST maintain in its Route Request Table, information about
   Route Requests that it initiates.  When initiating a new Route Error option,
         this field
   Request, the node MUST be set to 10, plus use the size of any
         Type-Specific Information present information recorded in the Route Error.  Further
         extensions to
   Request Table entry for the target of that Route Error option format may also be
         included after Request, and it MUST
   update that information in the Type-Specific Information portion of table entry for use in the next Route Error option specified above.
   Request initiated for this target.  In particular:

    -  The presence of such
         extensions will be indicated by the Opt Data Len field.
         When the Opt Data Len is greater than that required Route Request Table entry for a target node records the fixed portion
       Time-to-Live (TTL) field used in the IP header of the Route Error plus
       Request for the necessary
         Type-Specific Information as indicated last Route Discovery initiated by the Option Type this node for
       that target node.  This value in the option, allows the remaining octets are interpreted as
         extensions.  Currently, no such further extensions have been
         defined.

      Error Type

         The type node to implement a
       variety of error encountered.  Currently, algorithms for controlling the following type
         value is defined:

             1 = NODE_UNREACHABLE

         Other values spread of its Route
       Request on each Route Discovery initiated for a target.  As
       examples, two possible algorithms for this use of the Error Type TTL field
       are reserved described in Section 3.3.4.

    -  The Route Request Table entry for a target node records the
       number of consecutive Route Requests initiated for this target
       since receiving a valid Route Reply giving a route to that target
       node, and the remaining amount of time before which this node MAY
       next attempt at a Route Discovery for future
         use.

      Reservd

         Reserved.  Sent as 0; ignored on reception.

      Salvage that target node.

       A 4-bit unsigned integer.  Copied from the Salvage field in node MUST use these values to implement a back-off algorithm to
       limit the
         Source rate at which this node initiates new Route option of the packet triggering Discoveries
       for the same target address.  In particular, until a valid Route Error,
         incremented by the
       Reply is received for this target node returning address, the timeout
       between consecutive Route Error.

      Error Source Address

         The address of the Discovery initiations for this target
       node originating with the Route Error (e.g., same hop limit SHOULD increase by doubling the
       timeout value on each new initiation.

   The behavior of a node that attempted to forward processing a packet containing DSR header
   with both a DSR Source Route option and discovered the link
         failure).

      Error Destination Address

         The address of the node to which the a Route Error must be
         delivered For example, when the Error Type field Request option is set to
         NODE_UNREACHABLE, this field will
   unspecified.  Packets SHOULD NOT contain both a DSR Source Route
   option and a Route Request option.

   Packets containing a Route Request option SHOULD NOT include
   an Acknowledgement Request option, SHOULD NOT expect link-layer
   acknowledgement or passive acknowledgment, and SHOULD NOT be set to the address
   retransmitted.  The retransmission of packets containing a Route
   Request option is controlled solely by the logic described in this
   section.

6.2.2. Processing a Received Route Request Option

   When a node receives a packet containing a Route Request option, that generated the routing information claiming that the
         hop from the Error Source Address
   node MUST process the option according to Unreachable Node the following sequence of
   steps:

    -  If the Target Address
         (specified field in the Type-Specific Information) was Route Request matches this
       node's own IP address, then the node SHOULD return a valid hop.

      Type-Specific Information

         Information specific Route Reply
       to the Error Type initiator of this Route Error
         message.

   Currently, Request (the Source Address in the Type-Specific Information field is defined only for
   Route Error messages
       IP header of type NODE_UNREACHABLE.  In this case, the
   Type-Specific Information field is defined packet), as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Unreachable Node Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Unreachable Node Address described in Section 6.2.4.  The address of
       source route for this Reply is the node that was found to be unreachable
         (the next sequence of hop neighbor to which addresses

          initiator, Address[1], Address[2], ..., Address[n], target

       where initiator is the node with address
         Error Source Address was attempting to transmit of the packet).

   A initiator of this
       Route Error option MAY appear one or more times within a DSR
   header.

5.5. Acknowledgment Request Option

   The Acknowledgment Request DSR option Request, each Address[i] is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   ACK an address from the Route
       Request, and target is the target of the Route Request Source (the
       Target Address                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         5

      Opt Data Len

         8-bit unsigned integer.  Length of field in the option, Route Request).  The value n here
       is the number of addresses recorded in octets,
         excluding the Option Type and Opt Route Request, or
       (Opt Data Len fields.

      Identification - 6) / 4.

       The Identification node then MUST replace the Destination Address field is set to a unique nonzero in
       the Route Request packet's IP header with the value and
         is copied into in the Identification
       Target Address field of in the Acknowledgement
         option when returned by Route Request option, and continue
       processing the node receiving rest of the packet over this
         hop.

      ACK Route Request Source Address packet normally.  The address of the
       node requesting MUST NOT process the acknowledgment.

   An Acknowledgement Route Request option further and MUST
       NOT appear more than once
   within a DSR header.

5.6. Acknowledgment Option

   The Acknowledgment DSR option is encoded retransmit the Route Request to propagate it to other nodes
       as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |         Identification        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       ACK part of the Route Discovery.

    -  Else, the node MUST examine the route recorded in the Route
       Request option (the IP Source Address                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     ACK Destination Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         6

      Opt Data Len

         8-bit unsigned integer.  Length field and the sequence of
       Address[i] fields) to determine if this node's own IP address
       already appears in this list of addresses.  If so, the option, in octets,
         excluding node MUST
       discard the Option Type and Opt Data Len fields.

      Identification

         Copied from entire packet carrying the Identification field of Route Request option.

    -  Else, the Acknowledgement node MUST search its Route Request option of Table for an entry
       for the packet being acknowledged.

      ACK initiator of this Route Request (the IP Source Address

         The address of
       field).  If such an entry is found in the table, the node originating MUST
       search the acknowledgment.

      ACK Destination Address

         The address cache of the node Identification values of recently received
       Route Requests in that table entry, to which determine if an entry
       is present in the acknowledgment cache matching the Identification value
       and target node address in this Route Request.  If such an
       (Identification, target address) entry is to be
         delivered.

   An Acknowledgement option MAY appear one or more times within a DSR
   header.

5.7. Source found in this cache in
       this entry in the Route Option

   The Source Request Table, then the node MUST discard
       the entire packet carrying the Route DSR option is encoded as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Option Type  |  Opt Data Len |F|L|Reservd|Salvage| Segs Left |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[1]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[2]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Address[n]                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Option Type

         7

      Opt Data Len

         8-bit unsigned integer.  Length of Request option.

    -  Else, this node SHOULD further process the option, in octets,
         excluding Route Request
       according to the Option Type following sequence of steps:

        o  Add an entry for this Route Request in its cache of
           (Identification, target address) values of recently received
           Route Requests.

        o  Conceptually create a copy of this entire packet and Opt Data Len fields.  For perform
           the
         format following steps on the copy of the Source Route option defined here, packet.

        o  Append this field
         MUST be set node's own IP address to the value (n * 4) + 2, where n is the number list of
         addresses present Address[i]
           values in the Address[i] fields.

      First Hop External (F)

         Set to indicate that Route Request, and increase the first node indicated value of the
           Opt Data Len field in the Route Request by 4 (the size of an
           IP address).

        o  This node SHOULD search its own Route Cache for a route
           (from itself, as if it were the Source source of a packet) to the
           target of this Route option Request.  If such a route is actually found in
           its Route Cache, then this node SHOULD follow the procedure
           outlined in Section 6.2.3 to return a network external "cached Route Reply"
           to the DSR
         network; the exact sequence initiator of hops leading from it outside this Route Request, if permitted by the
         DSR network are not represented in
           restrictions specified there.

        o  If the Source node does not return a cached Route option.
         Nodes caching Reply, then this hop in their Route Cache MUST flag
           node SHOULD link-layer re-broadcast this copy of the
         cached hop packet,
           with a short jitter delay before the External flag.  Such hops MUST NOT broadcast is sent.  The
           jitter period SHOULD be
         returned in chosen as a random period, uniformly
           distributed between 0 and BroadcastJitter.

6.2.3. Generating a Route Reply generated from this Route Cache
         entry, and selection of routes from using the Route Cache to route
         a packet being sent SHOULD prefer routes that contain no hops
         flagged as External.

      Last Hop External (L)

         Set to indicate that the last hop indicated by the Source Route
         option is actually

   As described in Section 3.3.2, it is possible for a network external node processing a
   received Route Request to avoid propagating the DSR network; Route Request further
   toward the exact sequence target of hops leading to it outside the DSR
         network are not represented in the Source Route option.  Nodes
         caching Request, if this hop node has in their its Route Cache MUST flag the cached
         hop with the External flag.
   a route from itself to this target.  Such hops MUST NOT be returned
         in a Route Reply generated by
   a node from this Route Cache entry, and
         selection of routes from its own cached route to the target of a Route Cache to route Request is
   called a packet
         being sent SHOULD prefer routes that contain no hops flagged as
         External.

      Reserved

         Sent as 0; ignored on reception.

      Salvage

         A 4-bit unsigned integer.  Count of number of times that "cached Route Reply", and this packet has been salvaged as a part of DSR routing
         (Section 3.4.1).

      Segments Left (Segs Left)

         Number of route segments remaining, i.e., number of explicitly
         listed intermediate nodes still to be visited before reaching mechanism can greatly reduce
   the final destination.

      Address[1..n]

         The sequence of addresses overall overhead of Route Discovery on the source route.  In routing
         and forwarding the packet, network by reducing
   the source route flood of Route Requests.  The general processing of a received
   Route Request is processed as described in Sections 6.1.3 Section 6.2.2; this section specifies
   the additional requirements that MUST be met before a cached Route
   Reply may be generated and 6.1.5.

   When forwarding returned and specifies the procedure for
   returning such a packet along cached Route Reply.

   While processing a DSR source route using received Route Request, for a Source node to possibly
   return a cached Route option in the packet's DSR header, the Source Address field Reply, it MUST have in
   the packet's IP header is always set its Route Cache a route
   from itself to the address target of the packet's
   ultimate destination.  A node receiving a packet containing a DSR
   header with this Route Request.  However, before
   generating a Source cached Route option Reply for this Route Request, the node MUST examine
   verify that there are no duplicate addresses listed in the indicated source route to determine if it is
   accumulated in the intended next hop for Route Request together with the route from this
   node's Route Cache.  Specifically, there MUST be no duplicates among
   the following addresses:

    -  The IP Source Address of the packet and
   determine how to forward containing the packet, as defined Route Request,

    -  The Address[i] fields in Sections 6.1.4 the Route Request, and 6.1.5.

5.8. Pad1 Option

    -  The Pad1 DSR option is encoded as follows:

   +-+-+-+-+-+-+-+-+
   |  Option Type  |
   +-+-+-+-+-+-+-+-+

      Option Type

         0

   A Pad1 option MAY be included nodes listed in the Options field route obtained from this node's Route
       Cache, excluding the address of a DSR header
   in order to align subsequent DSR options, but such alignment is
   not required this node itself (this node
       itself is the common point between the route accumulated in the
       Route Request and the route obtained from the Route Cache).

   If any duplicates exist among these addresses, then the node MUST NOT be expected by nodes receiving packets
   containing
   send a DSR header. cached Route Reply.  The total length of a DSR header, indicated by node SHOULD continue to process the Payload Length
   field
   Route Request as described in Section 6.2.2.

   If the DSR header MUST be a multiple of 4 octets.  When
   building a DSR header in a packet, sufficient Pad1 or PadN options
   MUST be included in Route Request and the Options field of route from the DSR header to make Route Cache meet the
   total length
   restriction above, then the node SHOULD construct and return a multiple of 4 octets.

   If more than one consecutive octet of padding cached
   Route Reply as follows:

    -  The source route for this reply is being inserted in the Options field sequence of a DSR header, the PadN option, described next,
   SHOULD be used, rather than multiple Pad1 options.

   Note that hop addresses

          initiator, Address[1], Address[2], ..., Address[n], c-route

       where initiator is the format address of the Pad1 option initiator of this Route
       Request, each Address[i] is a special case; it does
   not have an Opt Data Len or Option Data field.

5.9. PadN Option

   The PadN DSR option address from the Route Request,
       and c-route is the sequence of hop addresses in the source route
       to this target node, obtained from the node's Route Cache.  In
       appending this cached route to the source route for the reply,
       the address of this node itself MUST be excluded, since it is encoded
       already listed as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
   |  Option Type  |  Opt Data Len |   Option Data
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - Address[n].

    -

      Option Type

         1

      Opt Data Len

         8-bit unsigned integer.  Length  Send a Route Reply to the initiator of the option, in octets,
         excluding Route Request, using
       the Option Type and Opt Data Len fields.

      Option Data

         A number procedure defined in Section 6.2.4.  The initiator of zero valued octets equal to the Opt Data Len.

   A PadN option MAY be included
       Route Request is indicated in the Options Source Address field of in the
       packet's IP header.

   If the node returns a cached Route Reply as described above, then
   the node MUST NOT propagate the Route Request further (i.e., the
   node MUST NOT rebroadcast the Route Request).  In this case, instead,
   if the packet contains no other DSR header
   in order to align subsequent options and contains no payload
   after the DSR options, but such alignment header (e.g., the Route Request is not required and MUST NOT be expected by nodes receiving packets
   containing piggybacked
   on a TCP or UDP packet), then the node SHOULD simply discard the
   packet.  Otherwise (if the packet contains other DSR header.

   The total length of a options or
   contains any payload after the DSR header, indicated by header), the Payload Length
   field in node SHOULD forward
   the DSR header MUST be a multiple packet along the cached route to the target of 4 octets.  When
   building a the Route Request.
   Specifically, if the node does so, it MUST use the following
   steps:

    -  Copy the Target Address from the Route Request option in the
       DSR header in a packet, sufficient Pad1 or PadN options
   MUST be included in to the Options Destination Address field of in the packet's IP
       header.

    -  Remove the Route Request option from the DSR header to make in the
   total length a multiple of 4 octets.

6. Detailed Operation

6.1. General Packet Processing

6.1.1. Originating a Packet

   When originating any
       packet, and add a node using DSR routing MUST perform Source Route option to the following sequence of steps: packet's DSR
       header.

    -  Search  In the DSR Source Route option, set the Address[i] fields
       to represent the source route found in this node's Route
       Cache to the original target of the Route Discovery (the
       new IP Destination Address of the packet).  Specifically,
       the node copies the hop addresses of the source route into
       sequential Address[i] fields in the DSR Source Route option,
       for a i = 1, 2, ..., n.  Address[1] here is the address of this
       node itself (the first address in the source route found from
       this node to the address given original target of the Route Discovery).  The
       value n here is the number of hop addresses in this source route,
       excluding the destination of the packet (which is instead already
       represented in the IP Destination Address field in the packet's header. IP
       header).

    -  If no such  Initialize the Segments Left field in the DSR Source Route option
       to n as defined above.

    -  The First Hop External (F) bit in the DSR Source Route option is
       copied from the External bit flagging the first hop in the source
       route for the packet, as indicated in the Route Cache.

    -  The Last Hop External (L) bit in the DSR Source Route option is found
       copied from the External bit flagging the last hop in the Route Cache, then perform
       Route Discovery source
       route for the Destination Address, packet, as described indicated in
       Section 6.2. the Route Cache.

    -  If  The Salvage field in the packet contains a DSR Source Route Request option, then replace option MUST be
       initialized to some nonzero value; the
       IP Destination Address particular nonzero value
       used SHOULD be MAX_SALVAGE_COUNT.  By initializing this field with the IP "limited broadcast"
       address (255.255.255.255) [3].

    -  Else, to
       a nonzero value, nodes forwarding or overhearing this node must have packet will
       not consider a route link to exist between the Destination IP Source Address of the
       packet (since otherwise a and the Address[1] address in the DSR Source Route Request would have
       been added option
       (e.g., they will not attempt to add this to their Route Cache as
       a link).  By choosing MAX_SALVAGE_COUNT as the packet).  If nonzero value to
       which the length of node initializes this field, nodes furthermore will not
       attempt to salvage this packet.

    -  Transmit the packet to the next-hop node on the new source route is
       greater than 1 hop, or if
       in the packet, using the forwarding procedure described in
       Section 6.1.5.

6.2.4. Originating a Route Reply

   A node determines originates a Route Reply in order to reply to request a DSR
       network-layer acknowledgement from received and
   processed Route Request, according to the first hop procedures described in
   Sections 6.2.2 and 6.2.3.  The Route Reply is returned in a Route
   Reply option (Section 5.3).  The Route Reply option MAY be returned
   to the initiator of the route,
       then insert Route Request in a separate IP packet, used
   only to carry this Route Reply option, or it MAY be included in any
   other IP packet being sent to this address.

   The Route Reply option MUST be included in a DSR header as described in Section 6.1.2, and
       insert a Source Route option, as described in Section 6.1.3.  The
       source route in the packet is initialized from the route
   returned to the
       Destination Address found in initiator.  To initialize the Route Cache. Reply option, the
   node performs the following sequence of steps:

    -  Transmit  The Option Type in the packet option MUST be set to the address given value 3.

    -  The Opt Data Len field in the next hop, using
       Route Maintenance option MUST be set to retransmit the packet if necessary, as
       described value
       (n * 4) + 3, where n is the number of addresses in Section 6.3.

6.1.2. Adding a DSR Header to a Packet

   A node originating a packet adds a DSR header to the packet, if
   necessary, source
       route being returned (excluding the Route Discovery initiator
       node's address).

    -  The Last Hop External (L) bit in the option MUST be
       initialized to carry information needed by 0.

    -  The Reserved field in the routing protocol.  A
   packet option MUST NOT contain more than one DSR header.  A DSR header is
   added be initialized to 0.

    -  The Route Request Identifier MUST be initialized to a packet by performing the following sequence
       Identifier field of steps
   (these steps assume that the packet contains no other headers Route Request that
   MUST be located this reply is sent in
       response to.

    -  The sequence of hop addresses in the packet before source route are copied into
       the DSR header):

    -  Insert a DSR header after Address[i] fields of the IP header but before any other
       header that may option.  Address[1] MUST be present.

    -  Set set to
       the Next Header field first-hop address of the DSR header to route after the Protocol
       number field initiator of the packet's IP header.

    -  Set
       Route Discovery, Address[n] MUST be set to the Protocol field last-hop address
       of the packet's IP header to source route (the address of the Protocol
       number assigned for a DSR header (???).

6.1.3. Adding a Source Route Option to a Packet

   A node originating a packet adds a Source Route option target node), and each
       other Address[i] MUST be set to the packet,
   if necessary, next address in sequence in order to carry
       the source route being returned.

   The Destination Address field in the IP header of hops from this
   originating node the packet carrying
   the Route Reply option MUST be set to the final destination address of the packet.
   Specifically, initiator
   of the node adding Route Discovery (i.e., for a Route Reply being returned in
   response to some Route Request, the IP Source Address of the Route option constructs
   Request).

   After creating and initializing the Source Route Reply option and modifies the IP
   packet according to containing it, send the
   following sequence of steps:

    -  A Source Route option, as described in Section 5.7, is created Reply.  In sending the Route
   Reply from this node (but not from nodes forwarding the Route Reply),
   this node SHOULD delay the Reply by a small jitter period chosen
   randomly between 0 and appended to BroadcastJitter.

   When returning any Route Reply in the DSR header case in which the packet (a DSR header is
       added, as described MAC protocol
   in Section 6.1.2, if use in the network is not already present).

    -  The number capable of Address[i] fields to include in transmitting unicast packets
   over uni-directional links, the source route used for routing
   the DSR Source Route option (n) is Reply packet MUST be obtained by reversing the number sequence
   of intermediate nodes hops in the Route Request packet (the source route for that is
   then returned in the packet (i.e., excluding address Route Reply).  This restriction on returning
   a Route Reply enables the Route Reply to test this sequence of
   hops for bi-directionality, preventing the
       originating node and Route Reply from being
   received by the final destination address initiator of the
       packet).  The Segments Left field in Route Discovery unless each of
   the hops over which the DSR Source Route option Reply is initialized equal to n.

    -  The Destination Address from returned (and thus each
   of the IP header is copied into
       Address[n] hops in the DSR Source source route being returned in the Reply) is
   bi-directional.

   If sending a Route option.

    -  The first hop Reply to the initiator of the source route for Route Request
   requires performing a Route Discovery, the Route Reply Option MUST
   be piggybacked on the packet is copied into that contains the Destination Address field in Route Request.  This
   piggybacking prevents a loop wherein the IP header.

    -  The remaining hops target of the source route for new Route
   Request (which was itself the packet are copied
       into sequential Address[i] fields in initiator of the Source original Route option,
       for i = 1, 2, ..., n-1.

    -  The First Hop External (F) bit
   Request) must do another Route Request in order to return its
   Route Reply.

   If sending the Source Route option is
       copied from Reply to the External bit flagging initiator of the first hop Route Request
   does not require performing a Route Discovery, a node SHOULD send a
   unicast Route Reply in response to every Route Request it receives
   for which it is the target node.

6.2.5. Processing a Received Route Reply Option

   Section 6.1.4 describes the
       source route general processing for the a received packet, as indicated
   including the addition of routing information from options in the
   packet's DSR header to the receiving node's Route Cache.

    -  The Last Hop External (L) bit in

   If the received packet contains a Route Reply, no additional special
   processing of the Source Route Reply option is
       copied from the External bit flagging the last hop node in the
       source route for the packet, as indicated required beyond what is
   described there.  As described in Section 4.1 anytime a node adds
   new information to its Route Cache (including the information added
   from this Route Cache.

6.1.4. Receiving a Packet

   When a Reply option), the node receives any SHOULD check each packet containing in
   its own Send Buffer (Section 4.2) to determine whether a DSR header, it MUST
   process the packet according route to the following sequence of steps:

    -  If the
   that packet's IP Destination Address now exists in the packet's IP header matches
       one of this receiving node's own IP address(es), remove Route
   Cache (including the DSR
       header and all information just added to the included DSR options in Cache).  If so,
   the header, packet SHOULD then be sent using that route and pass removed from the rest of
   Send Buffer.  This general procedure handles all processing required
   for a received Route Reply option.

6.3. Route Maintenance Processing

   Route Maintenance is the packet mechanism by which a source node S is able
   to detect, while using a source route to some destination node D,
   if the network layer.

    -  Examine and process each of the options (if any) in the DSR
       header in the order in which they occur in topology has changed such that it can no longer use
   its route to D because a link along the packet, skipping
       over route no longer works.  When
   Route Maintenance indicates that a source route is broken, S can
   attempt to use any Pad1 other route it happens to know to D, or PadN options.

   Any DSR routing information carried in can invoke
   Route Discovery again to find a packet SHOULD be examined
   and reflected in the node's new route for subsequent packets
   to D.  Route Cache, even if the options in
   the packet are not otherwise processed as described above.  In
   particular, the following routing information SHOULD be handled in Maintenance for this way:

    -  In route is used only when S is
   actually sending packets to D.

   Specifically, when forwarding a Route Request option, packet, a node MUST attempt to
   receive an acknowledgement for the accumulated route record,
       represented by packet from the IP Source Address next-hop node.  If
   no acknowledgement is received after MaxMaintRexmt retransmissions of
   the packet and by (after the
       sequence initial transmission of Address[i] entries in the Route Request option SHOULD
       be added to the node's Route Cache.

    -  In a Route Reply option, packet), the route record being returned,
       represented by node
   determines that the sequence link for this next-hop node of Address[i] entries in the Route
       Request option and by the Destination Address in the packet's IP
       header SHOULD be added to source route
   is "broken".  This acknowledgement from the node's next-hop node for Route Cache.

    -  In an Acknowledgement option,
   Maintenance can be implemented using a link-layer acknowledgement
   (Section 6.3.1), using a "passive acknowledgement" (Section 6.3.2),
   or using a network-layer acknowledgement (Section 6.3.3); the single link from
   particular strategy for retransmission timing depends on the
       ACK Source Address to type of
   acknowledgement mechanism used.  If no acknowledgment is received
   after MaxMaintRexmt retransmissions (if necessary), the ACK Destination Address node SHOULD be added
   originate a Route Error to the node's Route Cache.

    - original sender of the packet, as
   described in Section 6.3.4.

   In deciding whether or not to send a Route Error option, in response to
   attempting to forward a packet from some sender over a broken link,
   a node MUST limit the single link number of consecutive packets from a single
   sender that the
       Error Source Address node attempts to forward over this same broken
   link for which the Unreachable Node Address MUST
       be removed from the node's node chooses not to return a Route Cache.

    -  In Error; this
   requirement MAY be satisfied by returning a Source Route option, Error for each
   packet that the indicated source route SHOULD
       be added node attempts to forward over a broken link.

6.3.1. Using Link-Layer Acknowledgments

   If the node's Route Cache, subject MAC protocol in use provides feedback as to the conditions
       identified in Section 3.3.1.  The full sequence successful
   delivery of hops in the
       DSR Source Route option is a data packet (such as follows:

        *  The Source Address in the packet's IP header is provided by the first hop
           (the sender link-layer
   acknowledgement frame defined by IEEE 802.11 [11]), then the use
   of the packet).

        *  The sequence DSR Acknowledgement Request and Acknowledgement options
   is not necessary.  If such link-layer feedback is available, it
   SHOULD be used instead of hops

              Address[1], Address[2], ..., Address[n]

           follow immediately after any other acknowledgement mechanism
   for Route Maintenance, and the node SHOULD NOT use either passive
   acknowledgements or network-layer acknowledgements for Route
   Maintenance.

   When using link-layer acknowledgements for Route Maintenance, the
   retransmission timing and the timing at which retransmission attempts
   are scheduled are generally controlled by the particular link layer
   implementation in use in the IP Source Address network.  For example, in IEEE 802.11,
   the source
           route, where n link-layer acknowledgement is returned after the number data packet as
   a part of addresses in the packet, or
           (Opt Data Len - 2) / 4.

        *  The Destination Address in basic access method of of the packet's IP header is IEEE 802.11 Distributed
   Coordination Function (DCF) MAC protocol; the
           final destination of time at which the packet and
   acknowledgement is expected to arrive and the last hop of time at which the
           source route.

   In addition to next
   retransmission attempt (if necessary) will occur are controlled by
   the processing of received packets described above, MAC protocol implementation.

   When a node receives a link-layer acknowledgement for any packet in
   its Retransmission Buffer, that node SHOULD examine the remove that packet from
   its Retransmission Buffer, stopping Route Maintenance retransmissions
   for that packet.

6.3.2. Using Passive Acknowledgments

   When link-layer acknowledgements are not available, but passive
   acknowledgements [16] are available, passive acknowledgements SHOULD
   be used for Route Maintenance when originating or forwarding a packet
   along any hop other than the last hop (the hop leading to determine if the receipt IP
   Destination Address node of this
   packet indicates an opportunity the packet).  In particular, passive
   acknowledgements SHOULD be used for automatic route shortening, as
   described Route Maintenance in Section 3.4.2.  If the received packet satisfies such cases
   if the
   tests described there, then this node SHOULD perform can place its network interface into "promiscuous"
   receive mode, and network links used for data packets generally
   operate bi-directionally (such as when the following
   sequence of steps:

    -  Return a gratuitous MAC protocol requires
   this, as with IEEE 802.11).

   A node MUST NOT attempt to use passive acknowledgements for Route Reply
   Maintenance for a packet originated or forwarded over its last hop
   (the hop leading to the IP Source Destination Address node of the
       packet, as described in Section 3.4.2.

    -  Discard the received packet, packet),
   since the packet has been received
       before its normal traversal of receiving node will not be forwarding the packet's source route would
       have caused it packet and thus
   no passive acknowledgement will be available to reach be heard by this receiving
   node.  Another copy  Beyond this restriction, a node MAY utilize a variety of
   strategies in using passive acknowledgements for Route Maintenance of
   a packet that it originates or forwards.  For example, the following
   two strategies are possible:

    -  Each time a node receives a packet will normally arrive at this to be forwarded to a node as indicated in
       other than the packet's source route; discarding this initial copy final destination (the IP Destination Address
       of the
       packet, which triggered the gratuitous Route Reply, will prevent packet), that node sends the duplication original transmission of this packet
       that would otherwise occur.

6.1.5. Processing packet without requesting a Received Source Route Option network-layer acknowledgement
       for it.  If a no passive acknowledgement is received packet contains within
       PassiveAckTimeout after this transmission, the node retransmits
       the packet, again without requesting a DSR header with network-layer
       acknowledgement for it; the same PassiveAckTimeout timeout value
       is used for each such attempt.  If no acknowledgement has been
       received after a DSR Source Route
   option, total of TryPassiveAcks retransmissions of
       the Source Route option MUST be examined and processed (even
   though this packet, network-layer acknowledgements (as described in
       Section 6.3.3) are used for all remaining attempts for that
       packet.

    -  Each node is keeps a table of possible next-hop destination nodes,
       noting whether or not indicated in passive acknowledgements can typically
       be expected from transmission to that node, and the Destination Address field expected
       latency and jitter of
   the packet's IP header).

   If, after processing a Source Route option in passive acknowledgement from that node.
       Each time a received packet, an
   intermediate node determines that the receives a packet is to be forwarded onto to a link whose link MTU is less node
       other than the size of the packet, IP Destination Address, the node
   MUST discard the packet and send an ICMP Packet Too Big message checks its table
       of next-hop destination nodes to
   the packet's Source Address [23].

   A Source Route option in determine whether to use a DSR header
       passive acknowledgement or a network-layer acknowledgement for IPv4 is processed according
       that transmission to the following sequence of steps:

    -  If the value of the Segments Left field in the Source Route
       option equals 0, then remove the Source Route option that node.  The timeout for this packet
       can also be derived from the DSR
       header.

    -  Else, let n equal (Opt Data Len - 2) / 4.  This is the number of
       addresses in the Source Route option.

    -  If the value of the Segments Left field is greater than n, then
       send an ICMP Parameter Problem, Code 0, message [23] to the IP
       Source Address, pointing to the Segments Left field, and discard
       the packet.  Do not process the Source Route option further.

    -  Else, decrement the value of the Segments Left field by 1.  Let i
       equal n minus Segments Left.  This is the index of the next
       address this table.  A node using this method
       SHOULD prefer using passive acknowledgements to be visited in the Address vector.

    -  If Address[i] network-layer
       acknowledgements.

   In using passive acknowledgements for a packet that it originates or the IP Destination Address is
   forwards, a multicast
       address, then discard the packet.  Do not process the Source
       Route option further.

    -  Forward node considers the later receipt of a new packet (e.g.,
   with promiscuous receive mode enabled on its network interface) to be
   an acknowledgement of this first packet if both of the IP address specified following two
   tests succeed:

    -  The Source Address, Destination Address, Protocol,
       Identification, and Fragment Offset fields in the Address[i]
       field IP header
       of the IP two packets MUST match [27], and

    -  If either packet contains a DSR Source Route header, following normal IP forwarding
       procedures, including checking both packets
       MUST contain one, and decrementing the Time-to-Live
       (TTL) value in the Segments Left field in the packet's IP
       DSR Source Route header [24, 3].  In this
       forwarding of the packet, the next hop node (identified by
       Address[i]) new packet MUST be treated as a direct neighbor node; the
       transmission to less than that next node MUST be done
       in a single IP
       forwarding hop, without Route Discovery and without searching the
       Route Cache.

    -  In forwarding the packet, perform first packet.

   When a node hears such a passive acknowledgement for any packet in
   its Retransmission Buffer, that node SHOULD remove that packet from
   its Retransmission Buffer, stopping Route Maintenance retransmissions
   for the next
       hop of the packet, by verifying that packet.

6.3.3. Using Network-Layer Acknowledgments

   When a node originates or forwards a packet and has no other
   mechanism of acknowledgement available to determine successful
   delivery of the packet was received by
       that next hop, as described in Section 6.3.

   Multicast addresses MUST NOT appear to the next-hop node in a Source the source route
   for Route Maintenance, that node SHOULD request a network-layer
   acknowledgement from that next-hop node.  To do so, the node inserts
   an Acknowledgement Request option or in the IP Destination Address DSR header in the packet.
   The Identification field of a packet carrying a Source Route
   option in that Acknowledgement Request option MUST
   be set to a DSR header.

6.2. Route Discovery Processing

   Route Discovery is the mechanism value unique over all packets transmitted by which a this node S wishing to send a
   packet
   to a destination the same next-hop node D obtains that are either unacknowledged or recently
   acknowledged.

   When a source route to D.  Route
   Discovery is used only when S attempts to send node receives a packet to D and containing an Acknowledgement Request
   option, then that node performs the following tests on the packet:

    -  If the indicated next-hop node address for this packet does not already know a route to D.
       match any of this node's own IP addresses, then this node MUST
       NOT process the Acknowledgement Request option.  The indicated
       next-hop node initiating a Route
   Discovery address is known as the "initiator" of next Address[i] field in the DSR
       Source Route Discovery, and option in the
   destination node for which DSR header in the Route Discovery is initiated packet, or is known
   as the "target" of IP
       Destination Address in the Route Discovery.

   Route Discovery operates entirely on demand, with a node initiating
   Route Discovery based on its own origination of new packets for
   some destination address to which it packet if the packet does not currently know contain
       a
   route. DSR Source Route Discovery does not depend on any periodic or background
   exchange of routing information option or neighbor the Segments Left there is zero.

    -  If the packet contains an Acknowledgement option, then this node
       MUST NOT process the Acknowledgement Request option.

   If neither of the tests above fails, then this node detection at any
   layer in MUST process the network protocol stack at any node.

   The Route Discovery procedure utilizes two types
   Acknowledgement Request option by sending an Acknowledgement option
   to the previous-hop node; to do so, the node performs the following
   sequence of messages, steps:

    -  Create a Route
   Request (Section 5.2) packet and a Route Reply (Section 5.3), set the IP Protocol field to actively
   search the ad hoc network protocol
       number assigned for a route DSR header (TBA???).

    -  Set the IP Source Address field in this packet to the desired destination.
   These IP address
       of this node, copied from the source route in the DSR messages MAY be carried Source
       Route option in any type of that packet (or from the IP packet, through
   use Destination Address
       field of the packet, if the packet does not contain a DSR header as described in Section 5.

   A Source
       Route Discovery for a destination address SHOULD NOT be initiated
   unless option).

    -  Set the initiating node has a packet IP Destination Address field in its Send Buffer requiring
   delivery this packet to that destination.  A Route Discovery for a given target
   node MUST NOT be initiated unless permitted by the rate-limiting
   information contained IP
       address of the previous-hop node, copied from the source route
       in the DSR Source Route Request Table.  After each
   Route Discovery attempt, option in that packet (or from the interval between successive Route
   Discoveries for this target MUST be doubled, up to a maximum IP
       Source Address field of
   MAX_REQUEST_PERIOD, until a valid Route Reply is received for this
   target.

6.2.1. Originating a Route Request

   A node initiating the packet, if the packet does not
       contain a DSR Source Route Discovery for some target creates and
   initializes option).

    -  Add a Route Request DSR header to the packet, and set the DSR header's
       Next Header field to the "No Next Header" value.

    -  Add an Acknowledgement option in a to the DSR header in some IP packet.
   This MAY be a separate IP packet, used only the packet;
       set the Acknowledgement option's Option Type field to carry this Route
   Request option, or 6 and the node MAY include
       Opt Data Len field to 10.

    -  Copy the Route Identification field from the received Acknowledgement
       Request option into the Identification field in some existing packet it needs to send to the target node (e.g.,
       Acknowledgement option.

    -  Set the ACK Source Address field in the Acknowledgement option to
       be the IP packet originated by Source Address of this node, that caused the node new packet (set above to
   attempt Route Discovery for be the destination
       IP address of this node).

    -  Set the packet).
   The Route Request ACK Destination Address field in the Acknowledgement
       option MUST to be included in a DSR header in the
   packet.  To initialize IP Destination Address of this new packet (set
       above to be the IP address of the previous-hop node).

    -  Send the packet as described in Section 6.1.1.

   Packets containing an Acknowledgement option SHOULD NOT be
   retransmitted by intermediate nodes for Route Maintenance, and SHOULD
   NOT expect a link-layer acknowledgement or passive acknowledgment.

   When a node receives a packet with both an Acknowledgement option
   and an Acknowledgement Request option, the if that node performs is not the following sequence
   destination of steps:

    -  The Option Type in the Acknowledgement option MUST be set to (the IP Destination Address
   of the value 2.

    -  The Opt Data Len field in packet), then the Acknowledgement Request option MUST
   be set to ignored.  Otherwise (that node is the value 6.
       The total size destination of the Route
   Acknowledgement option), that node MUST process the Acknowledgement
   Request option when initiated
       is 8 octets; the Opt Data Len field excludes by returning an Acknowledgement option according to
   the size following sequence of the
       Option Type and Opt Data Len fields themselves. steps:

    -  The Identification field in the option MUST be  Create a packet and set the IP Protocol field to a new
       value, different from that used for other Route Requests recently
       initiated by this node.  For example, each node MAY maintain a
       single counter value the protocol
       number assigned for generating a new Identification value
       for each Route Request it initiates. DSR header (TBA???).

    -  The Target  Set the IP Source Address field in the option MUST be set this packet to the IP address that is the target
       of this Route Discovery.

   The node, copied from the source route in the DSR Source Address
       Route option in that packet (or from the IP header Destination Address
       field of this the packet, if the packet MUST be does not contain a DSR Source
       Route option).

    -  Set the node's
   own IP address.  The Destination Address field in the IP header of this packet MUST be to the IP "limited broadcast"
       address (255.255.255.255).

   A of the node MUST maintain in its Route Request Table, information about
   Route Requests that it initiates.  When initiating originating the Acknowledgement option.

    -  Add a new Route
   Request, DSR header to the node MUST use packet, and set the DSR header's
       Next Header field to the "No Next Header" value.

    -  Add an Acknowledgement option to the DSR header in this packet;
       set the Acknowledgement option's Option Type field to 6 and the
       Opt Data Len field to 10.

    -  Copy the information recorded in Identification field from the Route received Acknowledgement
       Request Table entry for the target of that Route Request, and it MUST
   update that information in option into the table entry for use Identification field in the next Route
   Request initiated for this target.  In particular:
       Acknowledgement option.

    -  The Route Request Table entry for a target node records  Set the
       Time-to-Live (TTL) ACK Source Address field used in the option to be the IP header
       Source Address of the last Route
       Request initiated by this node for that target node.  This
       value allows the node new packet (set above to implement a variety of algorithms
       for controlling be the spread IP address
       of its Route Request on each Route
       Discovery initiated for a target.  As examples, two possible
       algorithms for this use of node).

    -  Set the TTL ACK Destination Address field are described in
       Section 3.3.4.

    -  The Route Request Table entry for a target node records the
       number of consecutive Route Requests initiated for this target
       since receiving a valid Route Reply giving a route option to that target
       node, and be the remaining amount IP
       Destination Address of time before which this node MAY
       next attempt at a Route Discovery for that target node.

       These values MUST be used to implement an exponential back-off
       algorithm new packet (set above to limit be the rate at which this node initiates new
       Route Discoveries for IP
       address of the same target address.  Until a valid
       Route Reply is received for this target node address, originating the timeout
       between consecutive Route Discovery initiations for this target
       node SHOULD increase by doubling Acknowledgement option.)
    -  Send the timeout value on each new
       initiation. packet directly to the destination.  The behavior of IP
       Destination Address MUST be treated as a direct neighbor node:
       the transmission to that node processing a packet containing DSR header with
   both MUST be done in a Source single IP
       forwarding hop, without Route option Discovery and a without searching
       the Route Request option is unspecified.

   Packets SHOULD Cache.  In addition, this packet MUST NOT contain both a Source
       DSR Acknowledgement Request, MUST NOT be retransmitted for Route option
       Maintenance, and MUST NOT expect a link-layer acknowledgement or
       passive acknowledgment.

   When using network-layer acknowledgements for Route
   Request option.

   Packets containing Maintenance,
   a Route Request option SHOULD NOT be
   retransmitted, node SHOULD NOT request a DSR acknowledgment by including use an Acknowledgement Request option, adaptive algorithm in determining the
   retransmission timeout for each transmission attempt of a packet.
   For example, a node SHOULD NOT expect maintain a passive
   acknowledgment, separate round-trip time (RTT)
   estimate for each to which it has recently attempted to transmit
   packets, and it SHOULD NOT be placed use this RTT estimate in setting the Retransmission
   Buffer. timeout
   for each retransmission attempt for Route Maintenance.  The repeated transmission of packets containing TCP RTT
   estimation algorithm has been shown to work well for this purpose in
   implementation and testbed experiments with DSR [20, 22].

6.3.4. Originating a Route
   Request option Error

   When a node is controlled solely by unable to verify successful delivery of a packet to
   the logic described in this
   section.

6.2.2. Processing next-hop node after reaching a maximum number of retransmission
   attempts, a node SHOULD send a Received Route Request Option Error to the IP Source Address
   of the packet.  When sending a node receives Route Error for a packet containing
   either a Route Request Error option or an Acknowledgement option, a node
   SHOULD add these existing options to its Route Error, subject to the
   limit described below.

   A node transmitting a Route Error MUST process the option according to perform the following sequence of steps:

    -  If  Create an IP packet and set the Target Source Address field in the Route Request matches this
       node's own
       packet's IP address, then the node SHOULD return a Route Reply header to the initiator address of this Route Request (the node.

    -  If the Salvage field in the DSR Source Address Route option in the
       IP header of
       packet triggering the packet), as described in Section 6.2.4.  The
       source route for this reply Route Error is zero, then copy the sequence
       Source Address field of hops

          initiator, Address[1], Address[2], ..., Address[n], target

       where initiator is the address of packet triggering the initiator of this Route
       Request, each Address[i] is an address Error
       into the Destination Address field in the new packet's IP
       header; otherwise, copy the Address[1] field from the DSR Source
       Route Request,
       and target is the target option of the packet triggering the Route Request (the Target Error into the
       Destination Address field in the new packet's IP header

    -  Insert a DSR header into the new packet.

    -  Add a Route Request).

       The node MUST then continue processing Error Option to the rest new packet, setting the Error
       Type to NODE_UNREACHABLE, the Salvage value to the Salvage
       value from the DSR Source Route option of the packet
       normally.  The node in this case MUST NOT retransmit triggering
       the Route
       Request to propagate it Error, and the Unreachable Node Address field to other nodes.  Do not process
       the Route
       Request option further.

    -  Else, address of the next-hop node MUST examine from the route recorded in original source
       route.  Set the Error Source Address field to this node's IP
       address, and the Error Destination field to the new packet's IP
       Destination Address.

    -  If the packet triggering the Route
       Request option (the IP Source Address field and Error contains any Route Error
       or Acknowledgement options, the sequence of
       Address[i] fields) node MAY append to determine if this node's own IP address
       already appears in this list its Route
       Error each of addresses.  If so, these options, with the following constraints:

        o  The node MUST
       discard NOT include any Route Error option from the entire
           packet carrying the Route Request option.

    -  Else, triggering the node MUST search its new Route Request Table for an entry Error, for which the initiator total
           salvage count (Section 5.4) of this that included Route Request (the IP Source Address
       field). Error
           would be greater than MAX_SALVAGE_COUNT in the new packet.

        o  If such an entry any Route Error option from the packet triggering the new
           Route Error is found not included in the table, packet, the node MUST
       search NOT
           include any following Route Error or Acknowledgement options
           from the cache of Identification values of recently received packet triggering the new Route Requests in that table entry, to determine if an entry
       is present in Error.

        o  Any appended options from the cache matching packet triggering the Identification value
       and target node address in this Route Request.  If such an
       (Identification, target address) entry is found in this cache in
       this entry
           Error MUST follow the new Route Error in the packet.

        o  In appending these options to the new Route Request Table, then Error, the node MUST discard order
           of these options from the entire packet carrying triggering the Route Request option. Error
           MUST be preserved.

    -  Else, this  Send the packet as described in Section 6.1.1.

6.3.5. Processing a Received Route Error Option

   When a node SHOULD further receives a packet containing a Route Error option, that
   node MUST process the Route Request Error option according to the following
   sequence of steps:

        *  Add an entry for this Route Request in

    -  The node MUST remove from its cache of
           (Identification, target address) values of recently received Route Requests.

        *  Create a copy of this entire packet and perform Cache the following
           steps on link from the copy of
       node identified by the packet.

        *  Append this node's own IP address Error Source Address field to the list of Address[i]
           values in the Route Request, and increase the value of node
       identified by the
           Opt Data Len Unreachable Node Address field (if this link is
       present in the its Route Request by 4 (the size of an
           IP address).

        *  This Cache).  If the node SHOULD search implements its own Route
       Cache for a route
           (from itself, as if it were the source of a packet) to the
           target of link cache, as described in Section 4.1, only this Route Request.  If such a route
       single link is found in removed; if the node implements its Route Cache, then this node SHOULD follow the procedure
           outlined in Section 6.2.3 to return Cache as
       a "cached Route Reply"
           to the initiator of path cache, however, all routes (paths) that use this Route Request, if permitted by the
           restrictions specified there.

        * link are
       removed.

    -  If the node does not return a cached option following the Route Reply, then Error is an Acknowledgement
       or Route Error option sent by this node SHOULD link-layer re-broadcast (that is, with
       Acknowledgement or Error Source Address equal to this node's
       address), copy of the packet,
           with a short jitter delay before the broadcast is sent.  The
           jitter period SHOULD be chosen as a random period, uniformly
           distributed between 0 and BROADCAST_JITTER.

6.2.3. Generating Route Replies using DSR options following the current Route Cache

   As
       Error into a new packet with IP Source Address equal to this
       node's own IP address and IP Destination Address equal to the
       Acknowledgement or Error Destination Address.  Transmit this
       packet as described in Section 3.3.2, it is possible for a node processing a
   received 6.1.1, with the salvage count
       in the DSR Source Route Request option set to avoid propagating the Salvage value of the
       Route Request further
   toward Error.

   In addition, after processing the target of Route Error as described above,
   the Request, if this node MAY initiate a new Route Discovery for any destination node
   for which it then has no route in its Route Cache as a route from itself to result of
   processing this target.  Such a Route Reply generated by
   a Error, if the node from its own cached has indication that a route
   to the target of a Route Request that destination is
   called a "cached Route Reply", and this mechanism can greatly reduce
   the overall overhead of Route Discovery on needed.  For example, if the network by reducing node has an open
   TCP connection to some destination node, then if the flood of Route Requests.  The general processing of a received
   Route Request is described in Section 6.2.2;
   this section specifies Route Error removed the additional requirements only route to that MUST be met before a cached destination from this
   node's Route
   Reply may be generated and returned and specifies the procedure for
   returning such Cache, then this node MAY initiate a cached new Route Reply.

   While processing a received Discovery
   for that destination node.  Any node, however, MUST limit the rate at
   which it initiates new Route Request, Discoveries for a node to possibly
   return a cached any single destination
   address, and any new Route Reply, it MUST have Discovery initiated in its Route Cache a route
   from itself to the target this way as part of
   processing this Route Request.  However, before
   generating a cached Route Reply for Error MUST conform to this Route Request, the limit.

6.3.6. Salvaging a Packet

   When an intermediate node MUST
   verify forwarding a packet detects through Route
   Maintenance that there are no duplicate addresses listed in the route
   accumulated in next-hop link along the Route Request together with route for that packet is
   broken (Section 6.3), if the node has another route from this
   node's Route Cache.  Specifically, there MUST be no duplicates among to the following addresses:

    -  The packet's
   IP Source Destination Address of the packet containing the Route Request,

    -  The Address[i] fields in the its Route Request, and

    -  The nodes listed in Cache, the node SHOULD "salvage"
   the packet rather than discarding it.  To do so using the route obtained from this node's found
   in its Route Cache, excluding the address of this node itself (this node
       itself is processes the common point between packet as follows:

    -  If the route accumulated MAC protocol in use in the network is not capable of
       transmitting unicast packets over uni-directional links, as
       discussed in Section 3.3.1, then if this packet contains a Route Request
       Reply option, remove and the route obtained from discard the Route Cache).

   If any duplicates exist among these addresses, then Reply option in the node MUST NOT
   send a cached Route Reply.  The node SHOULD continue to process
       packet; if the
   Route Request as described DSR header in Section 6.2.2.

   If the Route Request and packet then contains no DSR
       options, remove the route DSR header from the Route Cache meet packet.  If the
   restriction above, resulting
       packet then contains only an IP header, the node SHOULD construct NOT
       salvage the packet and return a cached instead SHOULD discard the entire packet.

       When returning any Route Reply as follows:

    -  The source route for this reply is the sequence of hops

          initiator, Address[1], Address[2], ..., Address[n], c-route

       where initiator is in the address of case in which the initiator of this Route
       Request, each Address[i] is an address from MAC
       protocol in use in the Route Request,
       and c-route network is the sequence not capable of hops in the source route to this
       target node, obtained from the node's Route Cache.  In appending
       this cached route to transmitting
       unicast packets over uni-directional links, the source route
       used for routing the reply, the address
       of this node itself MUST be excluded, since it is already listed
       as Address[n].

    -  Send a Route Reply to packet MUST be obtained by
       reversing the initiator sequence of the Route Request, using
       the procedure defined hops in Section 6.2.4.  The initiator of the Route Request packet (the
       source route that is indicated in the Source Address field then returned in the
       packet's IP header.

6.2.4. Originating a Route Reply

   A node originates Reply).  This
       restriction on returning a Route Reply in order to reply to a received and
   processed Route Request, according to the procedures described in
   Sections 6.2.2 and 6.2.3.  The Route Reply is returned in on salvaging a packet
       that contains a Route Reply option (Section 5.3).  The enables the Route Reply option MAY be returned to the initiator
       test this sequence of hops for bi-directionality, preventing the
       Route Request in a separate IP packet, used
   only to carry this Route Reply option, or it MAY be included in any
   other IP packet from being sent to this address.

   The received by the initiator of the Route
       Discovery unless each of the hops over which the Route Reply option MUST be included is
       returned (and thus each of the hops in a the source route being
       returned in the Reply) is bi-directional.

    -  Modify the existing DSR header Source Route option in the packet
   returned so
       that the Address[i] fields represent the source route found in
       this node's Route Cache to this packet's IP Destination Address.
       Specifically, the initiator.  To initialize node copies the hop addresses of the source
       route into sequential Address[i] fields in the DSR Source Route Reply
       option, for i = 1, 2, ..., n.  Address[1] here is the address
       of the salvaging node performs itself (the first address in the following sequence source
       route found from this node to the IP Destination Address of steps:

    - the
       packet).  The Option Type value n here is the number of hop addresses in this
       source route, excluding the option MUST be set to destination of the value 3. packet (which is
       instead already represented in the Destination Address field in
       the packet's IP header).

    -  The Opt Data Len  Initialize the Segments Left field in the DSR Source Route option MUST be set
       to the value
       (n * 4) + 3, where n as defined above.

    -  The First Hop External (F) bit in the DSR Source Route option is
       copied from the number of addresses External bit flagging the first hop in the source
       route being returned (excluding for the packet, as indicated in the Route Discovery initiator
       node's address). Cache.

    -  The Last Hop External (L) bit in the DSR Source Route option MUST be initialized
       to 0.

    -  The Reserved field is
       copied from the External bit flagging the last hop in the option MUST be initialized to 0.

    -  The Route Request Identifier MUST be initialized to source
       route for the packet, as indicated in the
       Identifier Route Cache.

    -  The Salvage field of in the DSR Source Route Request that this reply option is sent in
       response to.

    -  The sequence of addresses set to 1 plus
       the value of the source route are copied into Salvage field in the Address[i] fields DSR Source Route option of
       the option.  Address[1] MUST be set packet that caused the error.

    -  Transmit the packet to the first hop of next-hop node on the new source route after
       in the initiator of packet, using the forwarding procedure described in
       Section 6.1.5.

   As described in Section 6.3.4, the node in this case also SHOULD
   return a Route
       Discovery, Address[n] MUST be set Error to the last hop original sender of the source
       route (the address of packet.  If the target node),
   node chooses to salvage the packet, it SHOULD do so after originating
   the Route Error.

7. Protocol Constants and Configuration Variables

   Any DSR implementation MUST support the following configuration
   variables and each other Address[i] MUST support a mechanism enabling the value of these
   variables to be set modified by system management.  The specific variable
   names are used for demonstration purposes only, and an implementation
   is not required to use these names for the next address in sequence in configuration variables,
   so long as the source route
       being returned.

   The Destination Address field external behavior of the implementation is consistent
   with that described in this document.

   For each configuration variable below, the IP header of default value is specified
   to simplify configuration.  In particular, the packet carrying default values given
   below are chosen for a DSR network running over 2 Mbps IEEE 802.11
   network network interfaces using the Distributed Coordination
   Function (DCF) MAC with RTS and CTS [11, 5].

       BroadcastJitter                     10   milliseconds

       RouteCacheTimeout                  300   seconds

       SendBufferTimeout                   30   seconds

       RequestTableSize                    64   nodes
       RequestTableIds                     16   identifiers
       MaxRequestRexmt                     16   retransmissions
       MaxRequestPeriod                    10   seconds
       RequestPeriod                      500   milliseconds
       NonpropRequestTimeout               30   milliseconds

       RexmtBufferSize                     50   packets

       MaxMaintRexmt                        2   retransmissions

       TryPassiveAcks                       1   attempt
       PassiveAckTimeout                  100   milliseconds

       GratReplyHoldoff                     1   second

   In addition, the Route Reply option following protocol constant MUST be set to the address of the initiator supported by any
   implementation of the Route Discovery (i.e., for a Route Reply being returned in
   response to some Route Request, DSR protocol:

       MAX_SALVAGE_COUNT                   15   salvages

8. IANA Considerations

   This document proposes the IP Source Address use of the Route
   Request).

   After creating and initializing the Route Reply option and the a DSR header, which requires an IP
   packet containing it, send the Route Reply.
   Protocol number.

   In sending the Route
   Reply from this node (but not from nodes forwarding the Route Reply), addition, this node SHOULD delay document proposes use of the rely by value "No Next Header"
   (originally defined for use in IPv6) within an IPv4 packet, to
   indicate that no further header follows a small jitter period chosen
   randomly between 0 and BROADCAST_JITTER milliseconds.

   If the MAC layer above which DSR is operating requires
   bidirectionality for unidirectional transmissions, the Route
   Reply MUST be sent by reversing the sequence of hops header.

9. Security Considerations

   This document does not specifically address security concerns.  This
   document does assume that are stored all nodes participating in it.

   If sending a Route Reply the DSR protocol
   do so in good faith and without malicious intent to corrupt the originator
   routing ability of the Route Request
   requires performing a Route Discovery, the Route Reply Option MUST
   be piggybacked on network.  In mission-oriented environments
   where all the packet that contains nodes participating in the Route Request.  This
   piggybacking prevents DSR protocol share a loop wherein
   common goal that motivates their participation in the target of protocol, the new Route
   Request (which was itself
   communications between the originator of nodes can be encrypted at the original Route
   Request) must do another Route Request in order physical
   channel or link layer to return its Route
   Reply.

   If sending the Route Reply prevent attack by outsiders.

Appendix A. Link-MaxLife Cache Description

   As guidance to the originator implementors of DSR, the Route Request
   does not require performing Route Discovery, description below outlines
   the operation of a node SHOULD send possible implementation of a
   unicast Route Reply in response Cache for DSR
   that has been shown to every received Route Request
   targeted at it.

6.2.5. Processing a Route Reply Option

   Upon receiving a Route Reply, a node SHOULD extract the source route
   from the Route Reply and add outperform other other caches studied in
   detailed simulations.  Use of this routing information to its Route
   Cache.  The source route from design for the Route Reply Cache is the sequence
   recommended in implementations of hops

      initiator, Address[1], Address[2], ..., Address[n]

   where initiator DSR.

   This cache, called "Link-MaxLife" [9], is the value of the Destination Address field a link cache, in that each
   individual link (hop) in the IP header of the packet carrying the routes returned in Route Reply (the address
   of packets
   (or otherwise learned from the initiator header of the Route Discovery), and each Address[i] overhead packets) is added
   to a
   node through which unified graph data structure of this node's current view of the source route passes,
   network topology, as described in turn, on the Section 4.1.  To search for a route
   in this cache to some destination node, the target of sending node uses a graph
   search algorithm, such as the Route Discovery.  Address[n] is well-known Dijkstra's shortest-path
   algorithm, to find the address of current best path through the
   target.

   If graph to the Last Hop External (L) bit
   destination node.

   The Link-MaxLife form of link cache is set adaptive in that each link in
   the Route Reply, cache has a timeout that is determined dynamically by the caching
   node
   MUST flag according to its observed past behavior of the hop Address[n] two nodes at the
   ends of the link; in its Route Cache as External.

   Each addition, when selecting a route for a packet in the Send Buffer SHOULD then be checked
   being sent to see whether some destination, among cached routes of equal length
   (number of hops) to that destination, Link-MaxLife selects the information route
   with the longest expected lifetime (highest minimum timeout of any
   link in the Route Reply and now route).

   Specifically, in Link-MaxLife, a link's timeout in the Route Cache allows
   it to be sent immediately.

6.3. Route Maintenance Processing

   Route Maintenance
   is the mechanism chosen according to a "Stability Table" maintained by which the caching
   node.  Each entry in a node's Stability Table records the address of
   another node S is able to detect,
   while using and a source route to D, if factor representing the network topology has changed
   such that it can no longer use its route perceived "stability" of
   this node.  The stability of each other node in a node's Stability
   Table is initialized to D because InitStability.  When a link along from the route no longer works.  When Route Maintenance indicates a source
   route
   Cache is broken, S can attempt to use any other route it happens to
   know to D, or can invoke Route Discovery again to find used in routing a new route
   for subsequent packets to D.  Route Maintenance packet originated or salvaged by that
   node, the stability metric for this route each of the two endpoint nodes of that
   link is
   used only incremented by the amount of time since that link was last
   used, multiplied by StabilityIncrFactor (StabilityIncrFactor >= 1);
   when S is actually sending packets to D.

   When forwarding a packet, a node MUST attempt link is observed to receive an
   acknowledgement for break and the packet link is thus removed
   from the next hop.  If no
   acknowledgement is received, Route Cache (either due the node SHOULD return receipt of a Route Error for
   this link or due to exceeding the IP Source Address maximum number of the packet, as described in Section 6.3.3.
   A node's algorithm retransmission
   attempts for deciding whether Route Maintenance for a packet being originated or not to return
   forwarded by this node), the stability metric for each of the two
   endpoint nodes of that link is multiplied by StabilityDecrFactor
   (StabilityDecrFactor < 1).

   When a Route
   Error MUST NOT allow any node adds a new link to attempt its Route Cache, the node assigns a
   lifetime for that link in the Cache equal to send an unbounded number the stability of packets along the
   less "stable" of the two endpoint nodes for the link, except that a broken
   link without receiving is not allowed to be given a Route Error.

6.3.1. Using Network-Layer Acknowledgments lifetime less than MinLifetime.
   When a node retransmits link is used in a packet or has no other way to ensure
   successful delivery of route chosen for a packet originated or
   salvaged by this node, the link's lifetime is set to be at least
   UseExtends into the next hop, it MUST request a
   network-layer acknowledgement by placing inserting an Acknowledgement
   Request future; if the DSR header.  The Identification value contained in lifetime of that
   header MUST be unique over all packets delivered to link in the same next hop
   which are either unacknowledged or recently acknowledged.

   A
   Route Cache is already further into the future, the lifetime remains
   unchanged.

   When a node receiving an Acknowledgement Request MUST send an
   acknowledgement to using Link-MaxLife selects a route from its Route Cache
   for a packet being originated or salvaged by this node, it selects
   the shortest-length route that has the previous hop by performing longest expected lifetime
   (highest minimum timeout of any link in the route), as opposed to
   simply selecting an arbitrary route of shortest length.

   The following
   sequence configuration variables are used in the description
   of steps:

    -  Create a packet Link-MaxLife above.  The specific variable names are used for
   demonstration purposes only, and set an implementation is not required
   to use these names for these configuration variables.  For each
   configuration variable below, the IP Source Address default value is specified to
   simplify configuration.  In particular, the address default values given
   below are chosen for a DSR network where nodes move at relative
   velocities between 12 and 25 seconds per transmission radius.

       InitStability                       25   seconds
       StabilityIncrFactor                  4
       StabilityDecrFactor                  2

       MinLifetime                          1   second
       UseExtends                         120   seconds

Appendix B. Location of this node, DSR in the IP Destination Address ISO Network Reference Model

   When designing DSR, we had to determine at what layer within
   the address of protocol hierarchy to implement ad hoc network routing.  We
   considered two different options:  routing at the
       previous hop, link layer (ISO
   layer 2) and routing at the IP Protocol field network layer (ISO layer 3).  Originally,
   we opted to route at the protocol number
       reserved link layer for DSR headers. several reasons:

    -  Set  Pragmatically, running the DSR header's Next Header field to be protocol at the "No Next Header"
       value.

    -  Set link layer
       maximizes the Acknowledgement option's Option Type field to 6, number of mobile nodes that can participate in
       ad hoc networks.  For example, the protocol can route equally
       well between IPv4 [27], IPv6 [6], and IPX [32] nodes.

    -  Historically [13, 14], DSR grew from our contemplation of
       a multi-hop propagating version of the
       Opt Data Len field to 10. Internet's Address
       Resolution Protocol (ARP) [25], as well as from the routing
       mechanism used in IEEE 802 source routing bridges [24].  These
       are layer 2 protocols.

    -  Copy the Identification field from the Acknowledgement Request
       option into the Identification field  Technically, we designed DSR to be simple enough that it could
       be implemented directly in the Acknowledgement
       option.  Set firmware inside wireless network
       interface cards [13, 14], well below the ACK Source Address field layer 3 software within
       a mobile node.  We see great potential in this for DSR running
       inside a cloud of mobile nodes around a fixed base station,
       where DSR would act to transparently extend the option coverage range
       to these nodes.  Mobile nodes that would otherwise be the
       IP Source Address and the ACK Destination Address field unable
       to communicate with the IP
       Destination Address.

    -  Send the packet base station due to factors such as described in Section 6.1.1.

6.3.2. Using Link Layer Acknowledgments

   If explicit failure notifications are provided by the link layer,
       distance, fading, or local interference sources could then all packets are assumed to be correctly received by reach
       the
   next hop, base station through their peers.

   Ultimately, however, we decided to specify and to implement [20]
   DSR as a Route Error is sent only when an explicit failure
   notification layer 3 protocol, since this is made from the link layer.

   Nodes receiving a packet without an Acknowledgement Request Option
   do not need to send only layer at which we
   could realistically support nodes with multiple network interfaces of
   different types forming an explicit Acknowledgment to ad hoc network.

Appendix C. Implementation and Evaluation Status

   The initial design of the packet's
   originator, DSR protocol, including DSR's basic Route
   Discovery and Route Maintenance mechanisms, was first published in
   December 1994 [13], with significant additional design details and
   initial simulation results published in early 1996 [14].

   The DSR protocol has been extensively studied since then through
   additional detailed simulations.  In particular, we have implemented
   DSR in the link layer will notify ns-2 network simulator [23, 5] and performed extensive
   simulations of DSR using ns-2 (e.g., [5, 19]).  We have also
   conducted evaluations of different caching strategies documented in
   this draft [9].

   We have also implemented the originator if DSR protocol under the
   packet was not received properly.

6.3.3. Originating a Route Error

   When a node FreeBSD 2.2.7
   operating system running on Intel x86 platforms.  FreeBSD [8] is unable to verify successful delivery of a packet to
   the next hop after
   based on a maximum number variety of retransmission attempts,
   a node SHOULD send a Route Error to free software, including 4.4 BSD Lite from the IP Source Address
   University of California, Berkeley.  For the
   packet.  In addition, a node's algorithm for deciding whether or not
   to return a Route Error MUST NOT allow any node to attempt to send
   an unbounded number of packets along a broken link without receiving
   a Route Error.  When sending a Route Error for a packet containing
   either a Route Error option or an Acknowledgement option, a node
   SHOULD add these options to its Route Error, subject to some limit on
   lifetime.  Specifically, environments in which
   we define the "salvage count" of an option used it, this implementation is functionally equivalent to be the sum
   version of one plus the salvage count recorded DSR protocol specified in this draft.

   During the Source
   Route option plus the sum of 7 months from August 1998 to February 1999, we designed
   and implemented a full-scale physical testbed to enable the salvage counts
   evaluation of any Route Errors
   preceding that option.

   A node transmitting a Route Error MUST follow ad hoc network performance in the following steps:

    -  Create a packet field, in an actively
   mobile ad hoc network under realistic communication workloads.  The
   last week of February and set the IP Source Address to the address first week of March of 1999 included
   demonstrations of this node, the IP Destination Address testbed to the address IP Source
       Address a number of our sponsors and
   partners, including Lucent Technologies, Bell Atlantic, and DARPA.
   A complete description of the packet experiencing the error.

    -  Insert testbed is available as a Technical
   Report [20].

   We have since ported this implementation of DSR header into the packet.

    -  Add a Route Error Option, setting the Error Type to
       NODE_UNREACHABLE, the Reserved bits to 0, the Salvage value to
       one plus the Salvage value from the FreeBSD 3.3, and
   we have also added a preliminary version of Quality of Service (QoS)
   support for DSR. A demonstration of this modified version of DSR Source Route option, was
   presented in July 2000.  These QoS features are not included in this
   draft, and will be added later in a separate draft on top of the Unreachable Node Address to base
   protocol specified here.

   DSR has also been implemented under Linux by Alex Song at the address
   University of Queensland, Australia [31].  This implementation
   supports the next hop.  Set
       the Error Source Address to Intel x86 PC platform and the IP Source Address Compaq iPAQ.

   Several other independent groups have also used DSR as a platform for
   their own research, or and as a basis of comparison between ad hoc
   network routing protocols.

Changes from Previous Version of the Error
       Destination to Draft

   This appendix briefly lists some of the IP Destination Address.

    -  The node MAY append each Route Error and Acknowledgement
       option, major changes in order, from this
   draft relative to the packet experiencing previous version of this same draft,
   draft-ietf-manet-dsr-05.txt:

    -  Clarified how to handle Route Maintenance at the error,
       though it MUST exclude options with salvage counts greater original sender
       of a packet, which is slightly different than MAX_SALVAGE_TIMES. at an intermediate
       node forwarding the packet.

    -  Send  In the packet as described definition of the Route Cache in Section 6.1.1.

6.3.4. Processing 4.1, if there
       are multiple cached routes to a Route Error Option

   A node receiving destination, a Route Error node MUST process it as follows:

    -  Delete all prefer
       routes from the Route Cache that do not have a link from the
       Route Error Source Address to the Unreachable Node Address.

    -  If the option following the Route Error is an Acknowledgement
       or Route Error option sent by External flag set on any link; this node (that is,
       restriction was previously specified as a "SHOULD".  This change
       does not affect the operation of DSR with
       Acknowledgement or Error Source Address equal respect to this node's
       address), copy draft,
       since the DSR options following use of external links is outside the current Route
       Error into scope of this
       draft.

    -  Clarified that the Retransmission Buffer MAY be of limited size,
       and that when adding a new packet with IP Source Address equal to this
       node's own IP address and IP Destination Address equal to the
       Acknowledgement or Error Destination Address.  Transmit this
       packet as described in Section 6.1.1, with the salvage count in Retransmission Buffer,
       if the Source Route option set buffer size is insufficient to hold the Salvage value of new packet, the Route
       Error.

6.3.5. Salvaging a Packet

   When a node is unable to verify successful delivery of a
       new packet
   to SHOULD be silently discarded.

    -  Changed the next hop after a maximum number calculation of retransmission attempts
   and has transmitted the Salvage field in a Route
       Error to option and the sender, it MAY attempt to total salvage the packet by examining its route cache.  If the node can
   find a route count of an option to not
       explicitely increment the packet's IP Destination Address in its own Route
   Cache, then this node replaces count when the packet's count is copied from a
       DSR Source Route option
   with into a new Source Route option in Error option.  Instead,
       the same way as described increment is implicit in
   Section 6.1.3, except that Address[1] MUST be set to the address of
   this node and the Salvage field MUST be set to 1 plus the value of the Salvage field
       and is added in when the Source Route option that caused the error.

7. Constants

   BROADCAST_JITTER                        10   milliseconds

   MAX_ROUTE_LEN                           15   nodes

   MAX_SALVAGE_TIMES                       15   salvages

   Route Cache
       ROUTE_CACHE_TIMEOUT                300   seconds

   Send Buffer
       SEND_BUFFER_TIMEOUT                 30   seconds

   Route Request Table
       REQUEST_TABLE_SIZE                  64   nodes
       REQUEST_TABLE_IDS                   16   identifiers
       MAX_REQUEST_REXMT                   16   retransmissions
       MAX_REQUEST_PERIOD                  10   seconds
       REQUEST_PERIOD                     500   milliseconds
       NONPROP_REQUEST_TIMEOUT             30   milliseconds

   Retransmission Buffer
       DSR_RXMT_BUFFER_SIZE                50   packets

   Retransmission Timer
       DSR_MAXRXTSHIFT                      2

8. IANA Considerations

   This document proposes the use total salvage count of a DSR header, which requires an IP
   Protocol number. option is
       calculated.

    -  In addition, this document proposes use Section 5.2, corrected the specification of the value "No Next Header"
   (originally defined for use number of
       Address[i] fields present in IPv6) within an IPv4 packet, to
   indicate that no further header follows a DSR header.

9. Security Considerations

   This document does not specifically address security concerns.  This
   document does assume that all nodes participating in Route Request option.  The number
       of addresses present is indicated by the DSR protocol
   do so Opt Data Len field in good faith and without malicious intent to corrupt the
   routing ability of
       the network. option as n = (Opt Data Len - 6) / 4.

    -  In mission-oriented environments
   where all Section 6.1.3, corrected the nodes participating in specification of the steps for
       adding a DSR protocol share Source Route option to a
   common goal that motivates their participation packet.  As described
       elsewhere in the protocol, the
   communications between draft, the nodes can be encrypted at entire source route (excluding the physical
   channel or link layer to prevent attack by outsiders.

Appendix A. Location
       address of DSR in the ISO Network Reference Model

   When designing DSR, we had to determine at what layer within
   the protocol hierarchy to implement ad hoc network routing.  We
   considered two different options:  routing at the link layer (ISO
   layer 2) originating node and routing at the network layer (ISO layer 3).  Originally,
   we opted to route at final destination address
       of the link layer for several reasons:

    -  Pragmatically, running packet) is copied into the DSR protocol at the link layer
       maximizes Source Route option, and
       the number IP Destination Address of mobile nodes that can participate the packet is not changed when
       inserting the source route.

    -  Added a specific statement in
       ad hoc networks.  For example, the protocol can route equally
       well between IPv4 [24], IPv6 [7], abstract and IPX [27] nodes.

    -  Historically [12, 13], DSR grew from our contemplation introduction
       that this document specifies the operation of
       a multi-hop propagating version DSR only for
       IPv4.  Operation of DSR with IPv6 [6] will be covered in other
       documents.

    -  Removed the Internet's ACK Request Source Address
       Resolution Protocol (ARP) [22], field from the
       Acknowledgement Request option, as well this field was not used in
       standard DSR; instead, the address of the node requesting a DSR
       Acknowledgement is obtained as from the routing
       mechanism previous-hop address of the
       source route in the packet.  This field is, however, used in IEEE 802 source routing bridges [21].  These
       are layer 2 protocols.

    -  Technically, we designed DSR the
       "flow state" enhancement to DSR [10] and will be simple enough specified in
       that it could draft.

    -  The DSR header was previously specified to always be implemented directly in the firmware inside wireless network
       interface cards [12, 13], well below the layer 3 software within a mobile node.  We see great potential multiple
       of 4 octet in size; this for DSR running
       inside a cloud of mobile nodes around a fixed base station,
       where is now only required if any other
       headers follow the DSR would act to transparently extend header in the coverage range packet.

    -  Clarified the definition of salvaging to these nodes.  Mobile nodes that would otherwise be unable
       to communicate with a "SHOULD" rather
       than a "MAY".

    -  Added the base station due to factors such definition of the Gratuitous Route Reply Table as
       distance, fading, or local interference sources could then reach a new
       conceptual data structure in Section 4.4, and added corresponding
       uses of it in the base station through their peers.

   Ultimately, however, we decided to specify detailed operation.  This data structure and to implement [19]
       its use have always been a part of the DSR as simulation but had not
       previously been documented in the draft.

    -  Removed the Identification field from the definition of a layer 3 protocol, Route
       Reply option since this is it was not used in the only layer at which we
   could realistically support nodes with multiple network interfaces protocol.

    -  Removed the restriction that the value of
   different types forming the Identification
       field in an ad hoc network.

Appendix B. Implementation and Evaluation Status

   The DSR protocol has been implemented under Acknowledgement Request option needed to be nonzero;
       the FreeBSD 2.2.7
   operating system running on Intel x86 platforms.  FreeBSD value zero at one time had a special meaning in the protocol
       but no longer is based
   on used for this purpose.

    -  Added a variety description of free software, including 4.4 BSD Lite from the
   University a specific possible implementation of California, Berkeley.  For the environments
       Route Cache data structure, called "Link-MaxLife", in which
   we used it, this Appendix A.
       The actual choice of data structure implementation is functionally equivalent to use for
       the
   protocol specified Route Cache in this draft.

   During any DSR implementation is a local matter
       for each node and affects only performance, not correctness or
       interoperability; the 7 months from August 1998 to February 1999, we designed Link-MaxLife cache, however, has been
       studied extensively and implemented a full-scale physical testbed been shown to enable the
   evaluation outperform other types of ad hoc network performance
       cache implementations studied in the field, detailed simulation [9], and its
       use in DSR implementations is recommended.

    -  Changed most of the protocol constants to now be configuration
       variables, which MUST support a actively
   mobile ad hoc network under realistic communication workloads.
   The last week mechanism enabling the value of February
       these variables to be modified by system management.  Also, to
       be clear in the specification which values are variables now and
       which are constants, changed the first week of March included
   demonstrations names of this testbed all variables to a number be in
       MixedCase instead of our sponsors and
   partners, including Lucent Technologies, Bell Atlantic, and DARPA.
   A complete description ALL_CAPS.

    -  Changed name of the testbed is available as a Technical
   Report [19].

   The software was ported constant MAX_SALVAGE_TIMES to FreeBSD 3.3, and a preliminary version
   of Quality
       MAX_SALVAGE_COUNT.

    -  Changed the name of Service (QoS) support was added.  A demonstration the variable DsrMaxRxtShift to now
       be MaxMaintRexmt.  Also changed the name of
   this modified version the variable
       DsrRxmtBufferSize to now be RexmtBufferSize.

    -  Clarified the description of DSR was presented what to add to a node's Route Cache
       in July 2000.  Those QoS
   features are not included response to different options in this draft, the DSR header of a received
       packet, and will be coalesced this description into Section 6.1.4.

    -  In Section 6.3.5, added later a suggestion that a node, after
       processing a Route Error, MAY initiate a new Route Discovery for
       any destination node for which it then has no route in its Route
       Cache as a
   separate draft on top result of processing this Route Error, if the base protocol specified here.

   The DSR protocol node has been extensively studied using simulation; we
   have implemented DSR
       indication that a route to that destination is needed (e.g., an
       open TCP connection).  Such Route Discoveries MUST conform to the
       standard rate limiting for Route Discoveries.

    -  Clarified the retransmission timing for Route Maintenance
       retransmissions, in Section 6.3.

    -  Updated the ns-2 simulator [5, 18] implementation and conducted
   evaluations of different caching strategies documented evaluation description in this
   draft [9].

   Several independent groups have also used
       Appendix C to include mention of the implementation of DSR as a under
       Linux by Alex Song at the University of Queensland, Australia.
       This implementation supports the Intel x86 PC platform for their
   own research, or and as a basis the
       Compaq iPAQ.

    -  Changed the status of comparison between ad hoc network
   routing protocols. the document to indicate full conformance
       with all provisions of Section 10 of RFC 2026.

Acknowledgements

   The protocol described in this draft has been designed and developed
   within the Monarch Project, a research project at Rice University and
   (previously at Carnegie Mellon University which University) that is developing
   adaptive networking protocols and protocol interfaces to allow truly
   seamless wireless and mobile node networking [14, 6]. [15, 30].

   The authors would like to acknowledge the substantial contributions
   of Josh Broch in helping to design, simulate, and implement the DSR
   protocol.  Josh is currently on leave of absence from Carnegie Mellon
   University at AON Networks.  We thank him for his contributions to
   earlier versions of this draft.

   We would also like to acknowledge the assistance of Robert V. Barron
   at Carnegie Mellon University.  Bob ported our DSR implementation
   from FreeBSD 2.2.7 into FreeBSD 3.3.

References

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        Requirement Levels.  RFC 2119, March 1997.

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    [7] Ralph Droms.  Dynamic Host Configuration Protocol.  RFC 2131,
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Chair's Address

   The MANET Working Group can be contacted via its current chairs:

   M. Scott Corson                        Phone: +1 301 405-6630
   Institute for Systems Research 908 947-7033
   Flarion Technologies, Inc.             Email: corson@isr.umd.edu
   University of Maryland
   College Park, MD  20742 corson@flarion.com
   Bedminster One
   135 Route 202/206 South
   Bedminster, NJ  07921
   USA

   Joseph Macker                          Phone: +1 202 767-2001
   Information Technology Division        Email: macker@itd.nrl.navy.mil
   Naval Research Laboratory
   Washington, DC  20375
   USA

Authors' Addresses

   Questions about this document can also be directed to the authors:

   David B. Johnson                       Phone: +1 713 348-3063
   Rice University                        Fax:   +1 713 348-5930
   Computer Science Department, MS 132    Email: dbj@cs.rice.edu
   6100 Main Street
   Houston, TX 77005-1892
   USA

   David A. Maltz                         Phone: +1 650 688-3128
   AON Networks                           Fax:   +1 650 688-3119
   3045 Park Blvd.                        Email: dmaltz@cs.cmu.edu
   Palo Alto, CA 94306
   USA

   Yih-Chun Hu                            Phone: +1 412 268-3075
   Rice University                        Fax:   +1 412 268-5576
   Computer Science Department, MS 132    Email: yihchun@cs.cmu.edu
   6100 Main Street
   Houston, TX 77005-1892
   USA

   Jorjeta G. Jetcheva                    Phone: +1 412 268-3053
   Carnegie Mellon University             Fax:   +1 412 268-5576
   Computer Science Department            Email: jorjeta@cs.cmu.edu
   5000 Forbes Avenue
   Pittsburgh, PA  15213-3891
   USA