draft-ietf-manet-dsr-00.txt   draft-ietf-manet-dsr-01.txt 
IETF MANET Working Group Josh Broch IETF MANET Working Group Josh Broch
INTERNET-DRAFT David B. Johnson INTERNET-DRAFT David B. Johnson
David A. Maltz David A. Maltz
Carnegie Mellon University Carnegie Mellon University
13 March 1998 8 December 1998
The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks
<draft-ietf-manet-dsr-00.txt> <draft-ietf-manet-dsr-01.txt>
Status of This Memo Status of This Memo
This document is a submission to the Mobile Ad-hoc Networks (manet) This document is a submission to the Mobile Ad-hoc Networks (manet)
Working Group of the Internet Engineering Task Force (IETF). Working Group of the Internet Engineering Task Force (IETF).
Comments should be submitted to the Working Group mailing list at Comments should be submitted to the Working Group mailing list at
"manet@itd.nrl.navy.mil". Distribution of this memo is unlimited. "manet@itd.nrl.navy.mil". Distribution of this memo is unlimited.
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
skipping to change at page 1, line 48 skipping to change at page 1, line 48
Dynamic Source Routing (DSR) is a routing protocol designed Dynamic Source Routing (DSR) is a routing protocol designed
specifically for use in mobile ad hoc networks. The protocol allows specifically for use in mobile ad hoc networks. The protocol allows
nodes to dynamically discover a source route across multiple network nodes to dynamically discover a source route across multiple network
hops to any destination in the ad hoc network. When using source hops to any destination in the ad hoc network. When using source
routing, each packet to be routed carries in its header the complete, routing, each packet to be routed carries in its header the complete,
ordered list of nodes through which the packet must pass. A key ordered list of nodes through which the packet must pass. A key
advantage of source routing is that intermediate hops do not need advantage of source routing is that intermediate hops do not need
to maintain routing information in order to route the packets they to maintain routing information in order to route the packets they
receive, since the packets themselves already contain all of the receive, since the packets themselves already contain all of the
necessary routing information. This, coupled with the dynamic, necessary routing information. This, coupled with the dynamic,
on-demand nature of Route Discovery, completely eliminates the need on-demand nature of DSR's Route Discovery, completely eliminates the
for periodic router advertisements and link status packets, reducing need for periodic router advertisements and link status packets,
the overhead of DSR, especially during periods when the network significantly reducing the overhead of DSR, especially during periods
topology is stable and these packets serve only as keep-alives. when the network topology is stable and these packets serve only as
keep-alives.
Contents Contents
Status of This Memo i Status of This Memo i
Abstract i Abstract i
1. Introduction 1 1. Introduction 1
2. Assumptions 1 2. Assumptions 1
3. Terminology 2 3. Terminology 2
3.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 2 3.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 2
3.2. Specification Language . . . . . . . . . . . . . . . . . 4 3.2. Specification Language . . . . . . . . . . . . . . . . . 4
4. Protocol Overview 5 4. Protocol Overview 5
4.1. Route Discovery and Route Maintenance . . . . . . . . . . 5 4.1. Route Discovery and Route Maintenance . . . . . . . . . . 5
4.2. Packet Forwarding . . . . . . . . . . . . . . . . . . . . 6 4.2. Packet Forwarding . . . . . . . . . . . . . . . . . . . . 6
4.3. Conceptual Data Structures . . . . . . . . . . . . . . . 6 4.3. Multicast Routing . . . . . . . . . . . . . . . . . . . . 7
4.3.1. Route Cache . . . . . . . . . . . . . . . . . . . 6
4.3.2. Node Information Cache . . . . . . . . . . . . . 8
4.3.3. Send Buffer . . . . . . . . . . . . . . . . . . . 8
4.3.4. Retransmission Buffer . . . . . . . . . . . . . . 8
5. Packet Formats 10 5. Conceptual Data Structures 7
5.1. Destination Options Headers . . . . . . . . . . . . . . . 10 5.1. Route Cache . . . . . . . . . . . . . . . . . . . . . . . 7
5.1.1. DSR Route Request Option . . . . . . . . . . . . 11 5.2. Route Request Table . . . . . . . . . . . . . . . . . . . 9
5.1.2. DSR Route Reply Option . . . . . . . . . . . . . 13 5.3. Send Buffer . . . . . . . . . . . . . . . . . . . . . . . 9
5.1.3. DSR Route Error Option . . . . . . . . . . . . . 14 5.4. Retransmission Buffer . . . . . . . . . . . . . . . . . . 9
5.1.4. DSR Acknowledgment Option . . . . . . . . . . . . 15
5.2. DSR Routing Header . . . . . . . . . . . . . . . . . . . 17
6. Detailed Operation 19 6. Packet Formats 11
6.1. Route Discovery . . . . . . . . . . . . . . . . . . . . . 19 6.1. Destination Options Headers . . . . . . . . . . . . . . . 11
6.1.1. Originating a Route Request . . . . . . . . . . . 19 6.1.1. DSR Route Request Option . . . . . . . . . . . . 12
6.1.2. Processing a Route Request Option . . . . . . . . 19 6.2. Hop-by-Hop Options Headers . . . . . . . . . . . . . . . 14
6.1.3. Originating a Route Reply . . . . . . . . . . . . 20 6.2.1. DSR Route Reply Option . . . . . . . . . . . . . 15
6.1.4. Processing a Route Reply Option . . . . . . . . . 21 6.2.2. DSR Route Error Option . . . . . . . . . . . . . 17
6.2. Route Maintenance . . . . . . . . . . . . . . . . . . . . 21 6.2.3. DSR Acknowledgment Option . . . . . . . . . . . . 18
6.2.1. Originating a Route Error . . . . . . . . . . . . 21 6.3. DSR Routing Header . . . . . . . . . . . . . . . . . . . 20
6.2.2. Processing a Route Error Option . . . . . . . . . 21
6.2.3. Processing a DSR Acknowledgment Option . . . . . 22
6.3. Processing a Routing Header . . . . . . . . . . . . . . . 22
7. Optimizations 24 7. Detailed Operation 23
7.1. Leveraging the Route Cache . . . . . . . . . . . . . . . 24 7.1. Originating a Data Packet . . . . . . . . . . . . . . . . 23
7.1.1. Promiscuous Learning of Source Routes . . . . . . 24 7.2. Originating a Packet with a DSR Routing Header . . . . . 23
7.1.2. Answering Route Requests using the Route Cache . 25 7.3. Processing a Routing Header . . . . . . . . . . . . . . . 24
7.2. Route Discovery Using Expanding Ring Search . . . . . . . 25 7.4. Route Discovery . . . . . . . . . . . . . . . . . . . . . 25
7.3. Preventing Route Reply Storms . . . . . . . . . . . . . . 26 7.4.1. Originating a Route Request . . . . . . . . . . . 25
7.4. Piggybacking on Route Discoveries . . . . . . . . . . . . 27 7.4.2. Processing a Route Request Option . . . . . . . . 26
7.5. Discovering Shorter Routes . . . . . . . . . . . . . . . 27 7.4.3. Generating Route Replies using the Route Cache . 27
7.6. Rate Limiting the Route Discovery Process . . . . . . . . 28 7.4.4. Originating a Route Reply . . . . . . . . . . . . 28
7.7. Improved Handling of Route Errors . . . . . . . . . . . . 29 7.4.5. Processing a Route Reply Option . . . . . . . . . 29
7.5. Route Maintenance . . . . . . . . . . . . . . . . . . . . 30
7.5.1. Using Network-Layer Acknowledgments . . . . . . . 30
7.5.2. Using Link Layer Acknowledgments . . . . . . . . 32
7.5.3. Originating a Route Error . . . . . . . . . . . . 32
7.5.4. Processing a Route Error Option . . . . . . . . . 33
7.5.5. Salvaging a Packet . . . . . . . . . . . . . . . 33
8. Constants 30 8. Optimizations 35
8.1. Leveraging the Route Cache . . . . . . . . . . . . . . . 35
8.1.1. Promiscuous Learning of Source Routes . . . . . . 35
8.2. Preventing Route Reply Storms . . . . . . . . . . . . . . 36
8.3. Piggybacking on Route Discoveries . . . . . . . . . . . . 37
8.4. Discovering Shorter Routes . . . . . . . . . . . . . . . 37
8.5. Rate Limiting the Route Discovery Process . . . . . . . . 38
8.6. Improved Handling of Route Errors . . . . . . . . . . . . 39
9. IANA Considerations 31 9. Constants 40
10. Security Considerations 32 10. IANA Considerations 41
Location of DSR Functions in the ISO Model 33 11. Security Considerations 42
Implementation Status 34 Location of DSR Functions in the ISO Model 43
Acknowledgments 35 Implementation Status 44
Areas for Refinement 36 Acknowledgments 45
References 37 References 46
Chair's Address 39 Chair's Address 48
Authors' Addresses 40 Authors' Addresses 49
1. Introduction 1. Introduction
This document describes Dynamic Source Routing (DSR) [6, 7], a This document describes Dynamic Source Routing (DSR) [6, 7], a
protocol developed by the Monarch Project [8, 14] at Carnegie Mellon protocol developed by the Monarch Project [8, 14] at Carnegie Mellon
University for routing packets in a mobile ad hoc network [3]. University for routing packets in a mobile ad hoc network [3].
Source routing is a routing technique in which the sender of a packet Source routing is a routing technique in which the sender of a packet
determines the complete sequence of nodes through which to forward determines the complete sequence of nodes through which to forward
the packet; the sender explicitly lists this route in the packet's the packet; the sender explicitly lists this route in the packet's
header, identifying each forwarding "hop" by the address of the next header, identifying each forwarding "hop" by the address of the next
node to which to transmit the packet on its way to the destination node to which to transmit the packet on its way to the destination
host. node.
DSR offers a number of potential advantages over other routing DSR offers a number of potential advantages over other routing
protocols for mobile ad hoc networks. First, DSR uses no periodic protocols for mobile ad hoc networks. First, DSR uses no periodic
routing messages (e.g., no router advertisements and no link-level routing messages of any kind (e.g., no router advertisements and no
neighbor status messages), thereby reducing network bandwidth link-level neighbor status messages), thereby significantly reducing
overhead, conserving battery power, and avoiding the propagation of network bandwidth overhead, conserving battery power, reducing the
probability of packet collision, and avoiding the propagation of
potentially large routing updates throughout the ad hoc network. Our potentially large routing updates throughout the ad hoc network. Our
Dynamic Source Routing protocol is able to adapt quickly to changes Dynamic Source Routing protocol is able to adapt quickly to changes
such as host movement, yet requires no routing protocol overhead such as node movement, yet requires no routing protocol overhead
during periods in which no such changes occur. during periods in which no such changes occur.
In addition, DSR has been designed to compute correct routes in In addition, DSR has been designed to compute correct routes in
the presence of asymmetric (uni-directional) links. In wireless the presence of asymmetric (uni-directional) links. In wireless
networks, links may at times operate asymmetrically due to sources networks, links may at times operate asymmetrically due to sources
of interference, differing radio or antenna capabilities, or the of interference, differing radio or antenna capabilities, or the
intentional use of asymmetric communication technology such as intentional use of asymmetric communication technology such as
satellites. Due to the existence of asymmetric links, traditional satellites. Due to the existence of asymmetric links, traditional
link-state or distance vector protocols may compute routes that link-state or distance vector protocols may compute routes that do
do not work. DSR, however, will find a correct route even in the not work. DSR, however, will always find a correct route even in the
presence of asymmetric links. presence of asymmetric links.
2. Assumptions 2. Assumptions
We assume that all hosts wishing to communicate with other hosts We assume that all nodes wishing to communicate with other nodes
within the ad hoc network are willing to participate fully in the within the ad hoc network are willing to participate fully in the
protocols of the network. In particular, each host participating in protocols of the network. In particular, each node participating in
the network should also be willing to forward packets for other hosts the network should also be willing to forward packets for other nodes
in the network. in the network.
We refer to the minimum number of hops necessary for a packet to We refer to the minimum number of hops necessary for a packet to
reach from any host located at one extreme edge of the network to reach from any node located at one extreme edge of the network to
another host located at the opposite extreme, as the diameter of the another node located at the opposite extreme, as the diameter of the
network. We assume that the diameter of an ad hoc network will be network. We assume that the diameter of an ad hoc network will be
small (e.g., perhaps 5 or 10 hops), but may often be greater than 1. 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 Packets may be lost or corrupted in transmission on the wireless
network. A host receiving a corrupted packet can detect the error network. A node receiving a corrupted packet can detect the error
and discard the packet. and discard the packet.
We assume that hosts can enable a promiscuous receive mode on We assume that nodes can enable promiscuous receive mode on their
their wireless network interface hardware, causing the hardware to wireless network interface hardware, causing the hardware to
deliver every received packet to the network driver software without deliver every received packet to the network driver software without
filtering based on link-layer destination address. Although we do filtering based on link-layer destination address. Although we do
not require this facility, it is for example common in current LAN not require this facility, it is for example common in current LAN
hardware for broadcast media including wireless, and some of our hardware for broadcast media including wireless, and some of our
optimizations take advantage of it if available. Use of promiscuous optimizations take advantage of its availability. Use of promiscuous
mode does increase the software overhead on the CPU, but we believe mode does increase the software overhead on the CPU, but we believe
that wireless network speeds are more the inherent limiting factor to that wireless network speeds are more the inherent limiting factor
performance in current and future systems. We believe that portions to performance in current and future systems. We also believe
of the protocol are also suitable for implementation directly within that portions of the protocol are also suitable for implementation
a programmable network interface unit to avoid this overhead on the directly within a programmable network interface unit to avoid this
CPU. overhead on the CPU.
3. Terminology 3. Terminology
3.1. General Terms 3.1. General Terms
node
A device that implements IP.
router
A node that forwards IP packets not explicitly addressed to
itself.
host
Any node that is not a router.
link link
A communication facility or medium over which nodes can A communication facility or medium over which nodes can
communicate at the link layer, such as an Ethernet (simple or communicate at the link layer, such as an Ethernet (simple or
bridged). A link is the layer immediately below IP. bridged). A link is the layer immediately below IP.
interface interface
A node's attachment to a link. A node's attachment to a link.
prefix prefix
A bit string that consists of some number of initial bits of an A bit string that consists of some number of initial bits of an
address. address.
interface index interface index
An 8-bit quantity which uniquely identifies an interface among An 7-bit quantity which uniquely identifies an interface among
a given node's interfaces. a given node's interfaces. Each node can assign interface
indices to its interfaces using any scheme it wishes.
The index IF_INDEX_MA is reserved for use by Mobile IP [9]
mobility agents (home or foreign agents) to indicate that they
believe they can reach a destination via a connected internet
infrastructure. The index IF_INDEX_ROUTER is reserved for
use by routers not acting as Mobile IP mobility agents to
indicate that they believe they can reach the destination via a
connected internet infrastructure.
The distinction between the index for mobility agents and
the index for routers, allows mobility agents to advertise
their existence ``for free''. A node that processes a routing
header listing the interface index IF_INDEX_MA, can then send
a unicast Agent Solicitation to the corresponding address in
the routing header to obtain complete information about the
mobility services being provided.
link-layer address link-layer address
A link-layer identifier for an interface, such as IEEE 802 A link-layer identifier for an interface, such as IEEE 802
addresses on Ethernet links. addresses on Ethernet links.
packet packet
An IP header plus payload. An IP header plus payload.
piggybacking
Including two or more conceptually different types of data in
the same packet so that all data elements move through the
network together.
home address home address
An IP address that is assigned for an extended period of time An IP address that is assigned for an extended period of time
to a mobile node. It remains unchanged regardless of where to a mobile node. It remains unchanged regardless of where
the node is attached to the Internet [9]. If a node has more the node is attached to the Internet [9]. If a node has more
than one home address, it SHOULD select and use a single home than one home address, it SHOULD select and use a single home
address when participating in the ad hoc network. address when participating in the ad hoc network.
source route source route
A source route from node A to node B is an ordered list of home A source route from a node S to some node D is an ordered list
addresses, starting with the home address of node A and ending of home addresses and interface indexes that contains all the
with the home address of the node B. Between A and B, the information that would be needed to forward a packet through
source route includes an ordered list of all the intermediate the ad hoc network. For each node that will transmit the
hops between A and B, as well as the interface index of the packet, the source route provides the index of the interface
interface through which the packet should be transmitted to over which the packet should be transmitted, and the address of
reach the next hop. Note that the packet formats defined in the node which is intended to receive the packet.
Section 5.1 encode the Target Address (node B) separately,
instead of encoding it as the last hop on the source route. DSR Routing Headers as described in Section 6.3 use a more
compact encoding of the source route and do not explicitly list
address S in the Routing Header`, since it is carried as the IP
Source Address of the packet.
A source route is described as ``broken'' when the specific
path it describes through the network is not actually viable.
Route Discovery Route Discovery
The method in DSR by which a node A dynamically obtains a The method in DSR by which a node S dynamically obtains a
source route to node B that will carry packets through the source route to some node D that will be used by S to route
network from A to B. Performing a route discovery involves packets through the network to D. Performing a Route Discovery
sending one or more Route Request packets. involves sending one or more Route Request packets.
Route Maintenance Route Maintenance
The process in DSR of monitoring the status of a source route The process in DSR of monitoring the status of a source route
while in use, so that any link-failures along the source route while in use, so that any link-failures along the source route
can be detected and the broken source route removed from use. can be detected and the broken link removed from use.
3.2. Specification Language 3.2. Specification Language
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2]. document are to be interpreted as described in RFC 2119 [2].
4. Protocol Overview 4. Protocol Overview
4.1. Route Discovery and Route Maintenance 4.1. Route Discovery and Route Maintenance
A source routing protocol must solve two challenges, which DSR terms A source routing protocol must solve two challenges, which DSR terms
Route Discovery and Route Maintenance. Route Discovery is the Route Discovery and Route Maintenance. Route Discovery is the
mechanism whereby a node S wishing to send a packet to a destination mechanism whereby a node S wishing to send a packet to a destination
D obtains a source route to D. D obtains a source route to D.
Route Maintenance is the mechanism whereby S is able to detect, while Route Maintenance is the mechanism whereby S is able to detect, while
using a source route to D, if the network topology has changed such 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 hop along the 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 no longer works. When Route Maintenance indicates a source
route is broken, S can attempt to use any other route it happens to 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. know to D, or can invoke Route Discovery again to find a new route.
To perform Route Discovery, the source node S broadcasts a Route To perform Route Discovery, the source node S link-layer broadcasts
Request packet with a recorded source route listing only itself. a Route Request packet. Here, node S is termed the initiator of the
Each node that hears the Route Request forwards the Request if Route Discovery, and the node to which S is attempting to discover a
appropriate, adding its own address to the recorded source route in source route, say D, is termed the target of the Discovery.
this copy of the Request and rebroadcasts the packet. The forwarding
of Requests is constructed so that copies of the Request propagate Each node that hears the Route Request packet forwards a copy of the
hop-by-hop outward from the node initiating the Route Discovery, Request, if appropriate, by adding its own address to a source route
until either the target of the Request is found or until another node being recorded in the Request packet and then rebroadcasting the
is found that can supply a route to the target. Route Request.
The forwarding of Route Requests is constructed so that copies of the
Request propagate hop-by-hop outward from the node initiating the
Route Discovery, until either the target of the Request is found or
until another node is found that can supply a route to the target.
The basic mechanism of forwarding Route Requests forwards the Request The basic mechanism of forwarding Route Requests forwards the Request
if the node (1) is not the target of the Request and (2) is not if the node (1) is not the target of the Request, (2) is not already
already listed in the recorded source route in this copy of the listed in the recorded source route in this copy of the Request, and
Request. In addition, however, each node maintains an LRU cache of (3) has not recently seen another Route Request packet belonging to
recently received Route Requests and does not propagate any copies this same Route Discovery. A node can determine if it has recently
of a Request after the first, avoiding the overhead of forwarding seen such a Route Request, since each Route Request packet contains
additional copies that reach this node along different paths. Also, a unique identifier for this Route Discovery, generated by the
the Time-to-Live field in the IP header of the packet carrying the initiator of the Discovery. Each node maintains an LRU cache of the
Route Request MAY be used to limit the scope over which the Request unique identifier from each recently received Route Request. By not
will propagate, using the normal behavior of Time-to-Live defined by propagating any copies of a Request after the first, the overhead of
IP [12, 1]. Additional optimizations on the handling and forwarding forwarding additional copies that reach this node along different
of Route Requests are also used to further reduce the Route Discovery paths is avoided.
overhead. When the target of the Request (e.g., node D) receives the
Route Request, it copies the recorded source route into a Route Reply In addition, the Time-to-Live field in the IP header of the packet
packet which it then sends this Reply back to the initiator of the carrying the Route Request MAY be used to limit the scope over which
Route Request (e.g., node S). the Request will propagate, using the normal behavior of Time-to-Live
defined by IP [12, 1]. Additional optimizations on the handling and
forwarding of Route Requests are also used to further reduce the
Route Discovery overhead.
When the target of the Request (e.g., node D) receives the Route
Request, the recorded source route in the Request identifies the
sequence of hops over which this copy of the Request reached D.
Node D copies this recorded source route into a Route Reply packet
and sends this Route Reply back to the initiator of the Route Request
(e.g., node S).
All source routes learned by a node are kept in a Route Cache, which All source routes learned by a node are kept in a Route Cache, which
is used to further reduce the cost of Route Discovery. When a node is used to further reduce the cost of Route Discovery. When a node
wishes to send a packet, it examines its own Route Cache and performs wishes to send a packet, it examines its own Route Cache and performs
Route Discovery only if no suitable source route is found in its Route Discovery only if no suitable source route is found in its
Cache. Cache.
Further, when a node B receives a Route Request from S for another Further, when some intermediate node B receives a Route Request from
node D, B searches its own Route Cache for a route to D. If B finds S for some target node D, B not equal D, B searches its own Route
such a route, it does not propagate the Route Request, but instead Cache for a route to D. If B finds such a route, it might not have
returns a Route Reply to node S based on the concatenation of the to propagate the Route Request, but instead return a Route Reply to
recorded source route from S to B in the Route Request and the cached node S based on the concatenation of the recorded source route from
route from B to D. The details of replying from a Route Cache in this S to B in the Route Request and the cached route from B to D. The
way are discussed in Section 7.1. details of replying from a Route Cache in this way are discussed in
Section 8.1.
As a node overhears routes being used by others, either by As a node overhears routes being used by others, either on data
promiscuously snooping on them or when forwarding packets, the node packets or on control packets used by Route Discovery or Route
MAY insert those routes into its Route Cache, leveraging the Route Maintenance, the node MAY insert those routes into its Route Cache,
Discovery operations of the other nodes. leveraging the Route Discovery operations of the other nodes in
the network. Such route information MAY be learned either by
promiscuously snooping on packets or when forwarding packets.
4.2. Packet Forwarding 4.2. Packet Forwarding
To represent a source route within a packet's header, DSR uses a To represent a source route within a packet's header, DSR uses a
Routing Header that conforms to the Routing Header format specified Routing Header similar to the Routing Header format specified for
for IPv6, adapted to the needs of DSR and to the use of the DSR in IPv6, adapted to the needs of DSR and to the use of DSR in IPv4 (or
IPv4 (or in IPv6 in the future). The DSR Routing Header uses a in IPv6 in the future). The DSR Routing Header uses a unique Routing
unique Routing Type field value to distinguish it from the existing Type field value to distinguish it from the existing Type 0 Routing
Type 0 Routing Header defined within IPv6 [4]. Header defined within IPv6 [4].
To forward a packet, a receiving node N simply processes the Routing To forward a packet, a receiving node N simply processes the Routing
Header as specified in the IPv6 [4] and transmits the packet to Header as specified in Section 7.3 and transmits the packet to
the next hop. If a forwarding error occurs along the link to the next hop. If a forwarding error occurs along the link to the
the next hop in the route, this node N sends a Route Error back next hop in the route, this node N sends a Route Error back to the
to the originator S of the packet informing S that this link is originator S of this packet informing S that this link is "broken".
"broken". If node N's Route Cache contains a different route to the If node N's Route Cache contains a different route to the destination
destination, then the packet is retransmitted using the new source of the original packet, then the packet is salvaged using the new
route. Each node overhearing or forwarding a Route Error packet also source route (Section 7.5.5). Otherwise, the packet is dropped.
Each node overhearing or forwarding a Route Error packet also
removes from its Route Cache the link indicated to be broken, thereby removes from its Route Cache the link indicated to be broken, thereby
cleaning the stale cache data from the network. cleaning the stale cache data from the network.
4.3. Conceptual Data Structures 4.3. Multicast Routing
All information a node needs for participation in an ad hoc At this time DSR does not support true multicasting. However, it
network using the Dynamic Source Routing Protocol can be organized does support the controlled flooding of a data packet to all nodes in
conceptually into four data structures: a Route Cache, a Node the network that are within some number of hops of the originator.
Information Cache, a Send Buffer, and a Retransmission Buffer. These While this mechanism does not support pruning of the broadcast
tree to conserve network resources, it can be used to distribute
information to nodes in the network.
When an application on a DSR node sends a packet to a multicast
address, DSR piggybacks the data from the packet inside a Route
Request packet targeted at the multicast address. The normal Route
Request distribution scheme described in Sections 4.1 and 7.4.2
will result in this packet being efficiently distributed to all
nodes in the network within the specified TTL of the originator.
The receiving nodes can then do destination address filtering on
the packet, discarding it if they do not wish to receive multicast
packets destined to this multicast address.
5. Conceptual Data Structures
In order to participate in the Dynamic Source Routing Protocol, a
node needs four conceptual data structures: a Route Cache, a Route
Request Table, a Send Buffer, and a Retransmission Buffer. These
data structures MAY be implemented in any manner consistent with the data structures MAY be implemented in any manner consistent with the
external behavior described in this document. external behavior described in this document.
4.3.1. Route Cache 5.1. Route Cache
All routing information needed by a node participating in an ad hoc All routing information needed by a node participating in an ad hoc
network is stored in a Route Cache. Each node in the network network using DSR is stored in a Route Cache. Each node in the
maintains its own Route Cache. The node adds information to the network maintains its own Route Cache. The node adds information
cache as it learns of new links between nodes in the ad hoc network, to the Cache as it learns of new links between nodes in the ad hoc
for example through packets carrying either a Route Reply or a network, for example through packets carrying either a Route Reply or
Routing Header. Likewise, the node removes information from the a Routing Header. Likewise, the node removes information from the
cache as it learns existing links in the ad hoc network have broken, cache as it learns existing links in the ad hoc network have broken,
for example through packets carrying a Route Error or through the for example through packets carrying a Route Error or through the
link-layer retransmission mechanism reporting a failure in forwarding link-layer retransmission mechanism reporting a failure in forwarding
a packet to its next-hop destination. The Route Cache is indexed a packet to its next-hop destination. The Route Cache is indexed
logically by destination node, and supports the following operations: logically by destination node address, and supports the following
operations:
void Insert(Route RT) void Insert(Route RT)
Information extracted from source route RT is inserted into the Inserts information extracted from source route RT into the
Route Cache. Route Cache.
Route Get(Node DEST) Route Get(Node DEST)
A source route from this node to DEST (if it exists) is Returns a source route from this node to DEST (if one is
returned. known).
void Delete(Node FROM, Node TO) void Delete(Node FROM, Interface INDEX, Node TO)
Any routes in the cache that assume the existence of a Removes from the route cache any routes which assume that a
unidirectional link from node FROM to node TO are removed from packet transmitted by node FROM over its interface with the
the cache. given INDEX will be received by node TO.
Each implementation MAY choose the cache replacement and cache search Each implementation MAY choose the cache replacement and cache search
strategies most appropriate for its particular network environment. strategies for its Route Cache that are most appropriate for its
For example, some environments may choose to return the shortest particular network environment. For example, some environments may
route to a node (the shortest sequence of hops), while others may choose to return the shortest route to a node (the shortest sequence
select an alternate metric for the Get() operation. of hops), while others may select an alternate metric for the Get()
operation.
The Route Cache SHOULD support storing more than one source route for The Route Cache SHOULD support storing more than one source route for
each destination. each destination.
If node S is using a source route to destination D that includes If there are multiple cached routes to a destination, the Route Get()
intermediate node I, S SHOULD shorten the route to destination D when operation SHOULD prefer routes that do not traverse a hop with an
it learns of a shorter route to node I. A node S using a source route interface index of IF_INDEX_MA or IF_INDEX_ROUTER. This will prefer
to destination D through node I, MAY shorten the source route if it routes that lead directly to the target node over routes that attempt
learns of a shorter path from node I to node D. to reach the target via any internet infrastructure connected to the
ad hoc network.
If a node S is using a source route to some destination D that
includes intermediate node N, S SHOULD shorten the route to
destination D when it learns of a shorter route to node N than the
one that is listed as the prefix of its current route to D.
A node S using a source route to destination D through intermediate
node N, MAY shorten the source route if it learns of a shorter path
from node N to node D.
The Route Cache replacement policy SHOULD allow routes to be The Route Cache replacement policy SHOULD allow routes to be
categorized based upon "preference", where routes with a higher categorized based upon "preference", where routes with a higher
preferences are less likely to be removed from the cache. For preferences are less likely to be removed from the cache. For
example, a node could prefer routes for which it initiated a Route example, a node could prefer routes for which it initiated a Route
Discovery over routes that it learned as the result of promiscuous Discovery over routes that it learned as the result of promiscuous
snooping. In particular, a node SHOULD prefer routes that it is snooping on other packets. In particular, a node SHOULD prefer
presently using over those that it is not. routes that it is presently using over those that it is not.
The Route Cache SHOULD time-stamp each route as it is inserted into
the cache. If the route is not used within ROUTE_CACHE_TIMEOUT
seconds, it SHOULD be removed from the cache.
4.3.2. Node Information Cache 5.2. Route Request Table
The Node Information Cache is a collection of records indexed by home The Route Request Table is a collection of records about Route
address. A record maintained on node N1 for node N2 contains the Request packets that were recently originated or forwarded by this
following: node. The table is indexed by the home address of the target of the
route discovery. A record maintained on node S for node D contains
the following:
- The time that N1 last began a Route Discovery for N2. - The time that S last originated a Route Discovery for D.
- The interval of time that N1 must wait before the next attempt at - The remaining amount of time that S must wait before the next
a Route Discovery for N2. attempt at a Route Discovery for D.
- The Time-to-live (TTL) field in the IP header of last Route - The Time-to-live (TTL) field in the IP header of last Route
Request transmitted by N1 for N2. Request originated by S for D.
- A FIFO cache of the last ID_FIFO_SIZE Identification values - A FIFO cache of the last ID_FIFO_SIZE Identification values from
observed in Route Request packets initiated by N2. Route Request packets targeted at node D that were forwarded by
this node.
Nodes SHOULD use an LRU policy to manage the entries of the Node Nodes SHOULD use an LRU policy to manage the entries of in their
Information Cache. Route Request Table.
4.3.3. Send Buffer ID_FIFO_SIZE MUST NOT be set to an unlimited value, since, in the
worst case, when a node crashes and reboots the first ID_FIFO_SIZE
Route Request packets it sends might appear to be duplicates to the
other nodes in the network.
The Send Buffer is a queue of packets that cannot be transmitted 5.3. Send Buffer
because the transmitting node does not yet have a source route
to the packets' destinations. Each packet in the Send Buffer is
stamped with the time that it is placed into the Buffer, and SHOULD
be removed from the Send Buffer and discarded SEND_BUFFER_TIMEOUT
seconds 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 6.1, a Route The Send Buffer of some node is a queue of packets that cannot be
Discovery SHOULD be initiated as often as possible for any packets transmitted by that node because it does not yet have a source
residing in the Send Buffer. route to each respective packet's destination. Each packet in the
Send Buffer is stamped with the time that it is placed into the
Buffer, and SHOULD be removed from the Send Buffer and discarded
SEND_BUFFER_TIMEOUT seconds 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.
4.3.4. Retransmission Buffer Subject to the rate limiting defined in Section 7.4, a Route
Discovery SHOULD be initiated as often as possible for the
destination address of any packets residing in the Send Buffer.
The Retransmission Buffer is a queue of packets that are awaiting the 5.4. Retransmission Buffer
receipt of an explicit acknowledgment from the next hop in the source
route (Section 5.2). The Retransmission Buffer of a node is a queue of packets sent by
this node that are awaiting the receipt of an acknowledgment from the
next hop in the source route (Section 6.3).
For each packet in the Retransmission Buffer, a node maintains (1) a For each packet in the Retransmission Buffer, a node maintains (1) a
count of the number of retransmissions and (2) the time of the last count of the number of retransmissions and (2) the time of the last
retransmission. retransmission.
Packets are removed from the buffer when an acknowledgment Packets are removed from the buffer when an acknowledgment
is received, or when the number of retransmissions exceeds is received, or when the number of retransmissions exceeds
MAX_EXPLICIT_REXMIT. In the later case, the removal of the packet DSR_MAXRXTSHIFT. In the later case, the removal of the packet from
from the Retransmission Buffer should result in a Route Error being the Retransmission Buffer SHOULD result in a Route Error being
returned to the initial source of the packet (Section 6.2). returned to the initial source of the packet (Section 7.5).
5. Packet Formats
5.1. Destination Options Headers 6. Packet Formats
Dynamic Source Routing makes use of four options carrying control Dynamic Source Routing makes use of four options carrying control
information that can be piggybacked in any existing IP packet. information that can be piggybacked in any existing IP packet.
The mechanism used for these options is based on the design of
the Destination Option mechanism in IPv6 [4]. This notion of The mechanism used for these options is based on the design of the
a Destination Option must be build in to a IPv4 protocol stack. Hop-by-Hop and Destination Options mechanisms in IPv6 [4]. The
Specifically, the Protocol field in the IP header should be used to ability to generate and process such options must be added to an IPv4
indicate that a Destination Options header exists between the IP protocol stack. Specifically, the Protocol field in the IP header
header and the remaining portion of a packet's payload (such as a is used to indicate that a Hop-by-Hop Options or Destination Options
transport layer header). The Next Header field in the Destination extension header exists between the IP header and the remaining
Options header will then indicate the type of header that follows it portion of a packet's payload (such as a transport layer header).
in a packet. The Next Header field in each extension header will then indicate the
type of header that follows it in a packet.
6.1. Destination Options Headers
The Destination Options header is used to carry optional information The Destination Options header is used to carry optional information
that need be examined only by a packet's destination node(s). The that need be examined only by a packet's destination node(s). The
Destination Options header is identified by a Next Header value of 60 Destination Options header is identified by a Next Header (or
in the immediately preceding header, and has the following format: Protocol) value of 60 in the immediately preceding header, and has
the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | | | Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| | | |
. . . .
. Options . . Options .
. . . .
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following destination options are used by the Dynamic Source Next Header
Routing protocol:
- DSR Route Request option (Section 5.1.1) 8-bit selector. Identifies the type of header immediately
following the Destination Options header. Uses the same values
as the IPv4 Protocol field [15].
- DSR Route Reply option (Section 5.1.2) Hdr Ext Len
- DSR Route Error option (Section 5.1.3) 8-bit unsigned integer. Length of the Destination Options
header in 4-octet units, not including the first 8 octets.
- DSR Acknowledgement option (Section 5.1.4) Options
All of these destination options MAY appear multiple times within a Variable-length field, of length such that the complete
Destination Options header is an integer multiple of 4 octets
long. Contains one or more TLV-encoded options.
The following destination option is used by the Dynamic Source
Routing protocol:
- DSR Route Request option (Section 6.1.1)
This destination option MUST NOT appear multiple times within a
single Destination Options header. single Destination Options header.
5.1.1. DSR Route Request Option 6.1.1. DSR Route Request Option
The DSR Route Request destination option is encoded in The DSR Route Request destination option is encoded in
type-length-value (TLV) format as follows: type-length-value (TLV) format as follows:
0 1 2 3 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 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 | Option Length | Identification | | Option Type | Option Length | Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Address | | Target Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index[1] | Index[2] | Index[3] | Index[4] | |C| IN Index[1] |C| IN Index[2] |C| IN Index[3] |C| IN Index[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|OUT Index[1] |C|OUT Index[2] |C|OUT Index[3] |C|OUT Index[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] | | Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] | | Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[3] | | Address[3] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[4] | | Address[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index[5] | Index[6] | Index[7] | Index[8] | |C| IN Index[5] |C| IN Index[6] |C| IN Index[7] |C| IN Index[8]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|OUT Index[5] |C|OUT Index[6] |C| OUT Index[7] |C|OUT Index[8]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[5] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP fields: IP fields:
Source Address Source Address
MUST be the home address of the node transmitting this packet. MUST be the home address of the node originating this packet.
Intermediate nodes that repropagate the request do not change
this field.
Destination Address Destination Address
MUST be the limited broadcast address (255.255.255.255). MUST be the limited broadcast address (255.255.255.255).
Hop Limit (TTL) Hop Limit (TTL)
Can be varied from 1 to 255, for example to implement Can be varied from 1 to 255, for example to implement
expanding-ring searches. expanding-ring searches.
Route Request fields: Route Request fields:
Option Type Option Type
???. A node that does not understand this option MUST discard ???. A node that does not understand this option MUST discard
the packet (the top two bits must be 01). the packet and the Option Data may change en-route (the top
three bits are 011).
Option Length Option Length
8-bit unsigned integer. Length of the option, in octets, 8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. excluding the Option Type and Option Length fields.
Identification Identification
A unique value generated by the initiator (original sender) A unique value generated by the initiator (original sender)
of the Route Request. This value allows a recipient to of the Route Request. This value allows a recipient to
determine whether or not it has recently seen this a copy of determine whether or not it has recently seen this a copy of
this Request; if it has, the packet is simply discarded. When this Request; if it has, the packet is simply discarded. When
propagating a Route Request, this field MUST be copied from the propagating a Route Request, this field MUST be copied from the
received copy of the Request being forwarded. received copy of the Request being forwarded.
Target Address Target Address
The home address of the node that is the target of the Route The home address of the node that is the target of the Route
Request. Request.
Index[1..n] Change Interface (C) bit[1..n]
Index[i] is the interface index of the ith hop recorded in in A flag associated with each interface index that indicates
the Route Request option (in Address[i]). whether or not the corresponding node repropagated the Request
over a different physical interface type than over which it
received the Request.
IN Index[1..n]
IN Index[i] is the index of the interface over which the node
indicated by Address[i] received the Route Request option.
These are used to record a reverse route from the target of
the request to the originator, over which a Route Reply MAY be
sent.
OUT Index[1..n]
OUT Index[i] is the interface index that the node indicated by
Address[i-1] used when rebroadcasting the Route Request option.
Address[1..n] Address[1..n]
Address[i] is the home address of the ith hop recorded in the Address[i] is the home address of the ith hop recorded in the
Route Request option. Route Request option.
5.1.2. DSR Route Reply Option 6.2. Hop-by-Hop Options Headers
The DSR Route Reply destination option is encoded in The Hop-by-Hop Options header is used to carry optional information
type-length-value (TLV) format as follows: that must be examined by every node along a packet's delivery path.
The Hop-by-Hop Options header is identified by a Next Header (or
Protocol) value of ??? in the IP header, and has the following
format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
8-bit selector. Identifies the type of header immediately
following the Hop-by-Hop Options header. Uses the same values
as the IPv4 Protocol field [15].
Hdr Ext Len
8-bit unsigned integer. Length of the Hop-by-Hop Options
header in 4-octet units, not including the first 8 octets.
Options
Variable-length field, of length such that the complete
Hop-by-Hop Options header is an integer multiple of 4 octets
long. Contains one or more TLV-encoded options.
The following hop-by-hop options are used by the Dynamic Source
Routing protocol:
- DSR Route Reply option (Section 6.2.1)
- DSR Route Error option (Section 6.2.2)
- DSR Acknowledgment option (Section 6.2.3)
All of these destination options MAY appear one or more times within
a single Hop-by-Hop Options header.
6.2.1. DSR Route Reply Option
The DSR Route Reply hop-by-hop option is encoded in type-length-value
(TLV) format as follows:
0 1 2 3 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 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 | Option Length |R|F| Reserved | | Option Type | Option Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Address | | Target Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index[1] | Index[2] | Index[3] | Index[4] | |C|OUT Index[1] |C|OUT Index[2] |C|OUT Index[3] |C|OUT Index[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] | | Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] | | Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[3] | | Address[3] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[4] | | Address[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index[5] | Index[6] | Index[7] | Index[8] | |C|OUT Index[5] |C|OUT Index[6] |C|OUT Index[7] |C|OUT Index[8] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[5] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type Option Type
???. A node that does not understand this option should ignore ???. A node that does not understand this option should ignore
this option and continue processing the packet (the top two this option and continue processing the packet, and the Option
bits should be 00). Data does not change en-route (the top three bits are 000).
Option Length Option Length
8-bit unsigned integer. Length of the option, in octets, 8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. excluding the Option Type and Option Length fields.
Router (R)
If the Router (R) bit is set, the last address recorded in this
header is the home address of a router that believes it can
reach the Target Address specified in the Route Request packet.
Foreign Agent (F)
If the Foreign Agent (F) bit is set, the last address recorded
in this header is the home address of an IETF Mobile IP [9]
Foreign Agent. The Router (R) bit and the Foreign Agent (F)
bit are mutually exclusive as (F) implies (R).
Reserved Reserved
Sent as 0; ignored on reception. Sent as 0; ignored on reception.
Target Address Target Address
The home address of the node that is the ultimate destination The home address of the node to which the Route Reply must be
of the source route contained in the Route Reply. delivered.
Index[1..n] Change Interface (C) bit[1..n]
Index[i] is the interface index of the ith hop listed in the If the C bit associated with a node N is set, it implies N will
Route Reply option (in Address[i]). be forwarding the packet out a different interface than the one
over which it was received (i.e., the node sending the packet
to N should not expect a passive acknowledgment).
OUT Index[1..n]
OUT Index[i] is the interface index of the ith hop listed in
the Route Reply option. It denotes the interface that should
be used by Address[i-1] to reach Address[i] when using the
specified source route.
Address[1..n] Address[1..n]
Address[i] is the home address of the ith hop listed in the Address[i] is the home address of the ith hop listed in the
Route Reply option. Route Reply option.
5.1.3. DSR Route Error Option 6.2.2. DSR Route Error Option
The DSR Route Error destination option is encoded in The DSR Route Error hop-by-hop option is encoded in type-length-value
type-length-value (TLV) format as follows: (TLV) format as follows:
0 1 2 3 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 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 | Option Length | Index | | Option Type | Option Length | Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address | | Error Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| From Hop Address | | Error Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Hop Address | | Unreachable Node Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type Option Type
???. A node that does not understand this option should ignore ???. A node that does not understand this option should ignore
the option and continue processing the packet (the top two bits the option and continue processing the packet, and the Option
must be 00). Data does not change en-route (the top three bits are 000).
Option Length Option Length
8-bit unsigned integer. Length of the option, in octets, 8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. excluding the Option Type and Option Length fields.
Index Index
The interface index of the network interface over which the The interface index of the network interface over which the
link from the From Hop Address node to the Next Hop Node is node designated by Error Source Address tried to forward a
being reported as broken by this Route Error option. This packet to the node designated by Unreachable Node Address.
Index refers to an interface on the From Hop Address node.
Originating Address Error Source Address
The home address of the node which originated the packet that The home address of the node originating the Route Error (e.g.,
could not be forwarded. the node that attempted to forward a packet and discovered the
link failure).
From Hop Address Error Destination Address
The home address of the node that attempted to forward a packet The home address of the node to which the Route Error must be
and discovered the link failure. delivered (e.g, the node that generated the routing information
claiming that the hop Error Source Address to Unreachable Node
Address was a valid hop).
Next Hop Address Unreachable Node Address
The home address of the node that was found to be unreachable The home address of the node that was found to be unreachable
(the next hop neighbor to which the node at Originating Address (the next hop neighbor to which the node at ``Error Source
was attempting to transmit the packet). Address'' was attempting to transmit the packet).
5.1.4. DSR Acknowledgment Option 6.2.3. DSR Acknowledgment Option
The DSR Acknowledgment destination option is encoded in The DSR Acknowledgment hop-by-hop option is encoded in
type-length-value (TLV) format as follows: type-length-value (TLV) format as follows:
0 1 2 3 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 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 | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Identification | | Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] | | ACK Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type Option Type
???. A node that does not understand this option should ignore ???. A node that does not understand this option should ignore
the option and continue processing the packet (the top two bits the option and continue processing the packet, and the Option
must be 00). Data does not change en-route (the top three bits are 000).
Option Length Option Length
8-bit unsigned integer. Length of the option, in octets, 8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. excluding the Option Type and Option Length fields.
Identification Identification
A unique value assigned by the originator of the packet. A 32-bit value that when taken in conjunction with Data Source
This value is used to match explicit acknowledgments to the Address, uniquely identifies the packet being acknowledged.
corresponding packet.
Address[1] The Identification value is computed as ((ip_id << 16) | ip_off)
where ip_id is the value of the 16-bit Identification field in
the IP header of the packet being acknowledged, and ip_off is
the value of the 13-bit Fragment Offset field in the IP header
of the packet being acknowledged.
The home address of the original source of the IP packet. When constructing the Identification, ip_id and ip_off MUST be
in host byte-order. The entire Identification value MUST then
be converted to network byte-order before being placed in the
Acknowledgment option.
5.2. DSR Routing Header ACK Source Address
The home address of the node originating the Acknowledgment.
ACK Destination Address
The home address of the node to which the Acknowledgment must
be delivered.
Data Source Address
The IP Source Address of the packet being acknowledged.
6.3. DSR Routing Header
As specified for IPv6 [4], a Routing header is used by a source to As specified for IPv6 [4], a Routing header is used by a source to
list one or more intermediate nodes to be "visited" on the way to list one or more intermediate nodes to be ``visited'' on the way to
a packet's destination. This function is similar to IPv4's Loose a packet's destination. This function is similar to IPv4's Loose
Source and Record Route option, but the Routing header does not Source and Record Route option, but the Routing header does not
record the route taken as the packet is forwarded. The specific record the route taken as the packet is forwarded. The specific
processing steps required to implement the Routing header must be processing steps required to implement the Routing header must be
added to an IPv4 protocol stack. The Routing header is identified by added to an IPv4 protocol stack. The Routing header is identified by
a Next Header value of 43 in the immediately preceding header, and a Next Header value of 43 in the immediately preceding header, and
has the following format: has the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left | | Next Header | Hdr Ext Len | Routing Type | Segments Left |
skipping to change at page 17, line 33 skipping to change at page 20, line 33
. . . .
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The type specific data for a Routing Header carrying a DSR Source The type specific data for a Routing Header carrying a DSR Source
Route is: Route is:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| Reserved | Identification | |R|S| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index[1] | Index[2] | Index[3] | Index[4] | |C|OUT Index[1] |C|OUT Index[2] |C|OUT Index[3] |C|OUT Index[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] | | Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] | | Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[3] | | Address[3] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[4] | | Address[4] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index[5] | Index[6] | Index[7] | Index[8] | |C|OUT Index[5] |C|OUT Index[6] |C|OUT Index[7] |C|OUT Index[8] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[5] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Routing Header Fields: Routing Header Fields:
Next Header Next Header
8-bit selector. Identifies the type of header immediately 8-bit selector. Identifies the type of header immediately
following the Routing Request header. following the Routing header.
Hdr Ext Len Hdr Ext Len
8-bit unsigned integer. Length of the Routing header in 8-bit unsigned integer. Length of the Routing header in
8-octet units, not including the first 8 octets. 4-octet units, not including the first 8 octets.
Routing Type Routing Type
??? ???
Segments Left Segments Left
Number of route segments remaining, i.e., number of explicitly Number of route segments remaining, i.e., number of explicitly
listed intermediate nodes still to be visited before reaching listed intermediate nodes still to be visited before reaching
the final destination. the final destination.
Type Specific Fields: Type Specific Fields:
Acknowledgment Request (R) Acknowledgment Request (R)
The Acknowledgment Request (R) bit is set to request an The Acknowledgment Request (R) bit is set to request an
explicit acknowledgment from the next hop. explicit acknowledgment from the next hop. After processing
the Routing Header, The IP Destination Address lists the
address of the next hop.
Salvaged Packet (S)
The Salvaged Packet (S) bit indicates that this packet has been
salvaged by an intermediate node, and thus that this Routing
Header was generated by Address[1] and not the IP Source
Address (Section 7.5.5).
Reserved Reserved
Sent as 0; ignored on reception. Sent as 0; ignored on reception.
Identification Change Interface (C) bit[1..n]
A unique value assigned by the originator of the packet. This If the C bit associated with a node N is set, it implies N will
value is used to match acknowledgments (passive or explicit) to be forwarding the packet out a different interface than the one
the appropriate packet. over which it was received (i.e., the node sending the packet
to N should not expect a passive acknowledgment and MAY wish to
set the R bit).
Index[1..n] OUT Index[1..n]
Index[i] is the interface index of the ith hop in the Routing Index[i] is the interface index that the node indicated
header. by Address[i-1] must use when transmitting the packet to
Address[i]. Index[1] indicates which interface the node
indicated by the IP Source Address uses to transmit the packet.
Address[1..n] Address[1..n]
Address[i] is the home address of the ith hop in the Routing Address[i] is the home address of the ith hop in the Routing
header. header.
6. Detailed Operation Note that Address[1] is the first intermediate hop along the route.
The address of the originating node is the IP Source Address. The
only exception to this rule is for packets that are salvaged, as
described in Section 7.5.5. A packet that has been salvaged has an
alternate route placed on it by an intermediate node in the network,
and in this case, the address of the originating node (the salvaging
node) is Address[1]. Salvaged packets are indicated by setting the S
bit in the DSR Routing header.
6.1. Route Discovery 7. Detailed Operation
Route Discovery is the demand-driven process by which nodes actively 7.1. Originating a Data Packet
When node A originates a packet, the following steps MUST be taken
before transmitting the packet:
1. If the destination address is a multicast address, piggyback the
data packet on a Route Request targeting the multicast address.
The following fields MUST be initialized as specified:
IP.Source_Address = Home address of node A
IP.Destination_Address = 255.255.255.255
Request.Target_Address = Multicast destination address
DONE.
2. Otherwise, call Route_Cache.Get() to determine if there is a
cached source route to the destination.
3. If the cached route indicates that the destination is directly
reachable over one hop, no Routing Header should be added to the
packet. Initialize the following fields:
IP.Source_Address = Home address of node A
IP.Destination_Address = Home address of the Destination
DONE.
4. Otherwise, if the cached route indicates that multiple hops are
required to reach the destination, insert a Routing Header into
the packet as described in Section 7.2. DONE.
5. Otherwise, if no cached route to the destination is found, insert
the packet into the Send Buffer and initiate Route Discovery as
described in Section 7.4.
7.2. Originating a Packet with a DSR Routing Header
When a node originates a packet with a Routing Header, the address
of the first hop in the source route MUST be listed as the IP
Destination Address as well as Address[1] in the Routing Header.
The final destination of the packet is listed as the last hop
in the Routing Header (Address[n]). At each intermediate hop i,
Address[i] is copied into the IP Destination Address and the packet
is retransmitted.
For example, suppose node A originates a packet destined for node D
that should pass through intermediate hops B and C. The packet MUST
be initialized as follows:
IP.Source_Address = Home address of node A
IP.Destination_Address = Home address of node B
RT.Segments_Left = 2
RT.Out_Index[1] = Interface index used by A to reach B
RT.Out_Index[2] = Interface index used by B to reach C
RT.Out_Index[3] = Interface index used by C to reach D
RT.Address[1] = Home address of node B
RT.Address[2] = Home address of node C
RT.Address[3] = Home address of node D
7.3. Processing a Routing Header
Excluding the exceptions listed here, a DSR Routing Header is
processed using the same rules as outlined for Type 0 Routing Headers
in IPv6 [4]. The Routing Header is only processed by the node whose
address appears as the IP destination of the packet. The following
additional rules apply to processing the type specific data of a DSR
Source Route:
Let
SegLft = the value of Segments Left when the packet was received
NumAddrs = the total number of addresses in the Routing Header
1. The address of the next hop, Address[NumAddrs - SegLft + 1],
is copied into the IP.Destination_Address of the packet. The
existing IP.Destination_Address is NOT copied back into the
Address list of the Routing Header.
2. The interface used to transmit the packet to its next hop from
this node MUST be the interface denoted by Index[NumAddrs -
SegLft + 1].
3. If the Acknowledgment Request (R) bit is set, the node MUST
transmit a packet containing the DSR Acknowledgment option to
the previous hop, Address[NumAddrs - SegLft - 1], performing
Route Discovery if necessary. (Address[0] is taken as the
IP.Source_Address)
4. Perform Route Maintenance by verifying that the packet was
received by the next hop as described in Section 7.5.
7.4. Route Discovery
Route Discovery is the on-demand process by which nodes actively
obtain source routes to destinations to which they are actively obtain source routes to destinations to which they are actively
attempting to send packets. The destination node for which a Route attempting to send packets. The destination node for which a
Discovery is initiated to discover a route is known as the "target" Route Discovery is initiated is known as the "target" of the Route
of the Route Discovery. A Route Discovery for a destination SHOULD Discovery. A Route Discovery for a destination SHOULD NOT be
NOT be initiated unless the initiating node has an unexpired packet initiated unless the initiating node has a packet in the Send Buffer
to be delivered to that destination. requiring delivery to that destination. A Route Discovery for a
given target node MUST NOT be initiated unless permitted by the
rate-limiting information contained in the Route Request Table.
After each Route Discovery attempt, the interval between successive
Route Discoveries for this target must be doubled, up to a maximum of
MAX_REQUEST_PERIOD.
A Route Discovery for a given target node MUST NOT be initiated Route Discoveries for a multicast address SHOULD NOT be rate limited,
unless the difference between the current time and the time that a and SHOULD always be permitted.
Route Discovery was last initiated for destination D is greater than
the backoff interval currently listed in the Node Information Cache
for node D. After each Route Discovery attempt, the interval between
successive Route Discoverys must be doubled, up to a maximum of
MAX_RTDISCOV_INTERVAL.
The basic Route Discovery algorithm is to originate a single 7.4.1. Originating a Route Request
Route Request packet as described below that targets the desired
destination and has a maximum hop limit set to MAX_ROUTE_LEN.
6.1.1. Originating a Route Request The basic Route Discovery algorithm for a unicast destination is as
follows:
A node originates a Route Request for a particular host when it has 1. Originate a Route Request packet with the IP header Time-to-Live
no route to that host. The Option Length field in the Route Request field initialized to 1. This type of Route Request is called a
option MUST be set to 6, the Identification field MUST be set to a non-propagating Route Request and allows the originator of the
unique number, and the Target Address field MUST contain the Home Request to inexpensively query the route caches of each of its
Address of the node for which a route is being requested. neighbors for a route to the destination.
6.1.2. Processing a Route Request Option 2. If a Route Reply is received in response to the non-propagating
Request, use the returned source route to transmit all packets
for the destination that are in the Send Buffer. DONE.
Let P1 be the received packet containing a Route Request option. 3. Otherwise, if no Route Reply is received within
Let P2 be a packet containing a corresponding Route Reply. A Route RING0_REQUEST_TIMEOUT seconds, transmit a Route Request
Request option is processed as follows: with the IP header Time-to-Live field initialized to
MAX_ROUTE_LEN. This type of Route Request is called a propagating
Route Request. Update the information in the Route Request
Table, to double the amount of time before any subsequent Route
Discovery attempt to this target.
1. Determine the originator of the Route Request. 4. If no Route Reply is received within the time interval indicated
by the Route Request Table, GOTO step 1.
If no addresses are presently listed in P1.REQUEST.Address[], The Route Request option SHOULD be initialized as follows:
then P1.Source_Address identifies the originator of the Route
Request. Otherwise, P1.REQUEST.Address[1] identifies the
originator of the Route Request.
2. If the combination (Originator Address, P1.REQUEST.Identification) IP.Source_Address = This node's home address
is in the node's cache of recently seen (Address, Identification) IP.Destination_Address = 255.255.255.255
pairs, then discard the packet. DONE. Request.Target = Home address of intended destination
Request.OUT_Index[1] = Index of interface used to transmit the Request
3. If the home address of this node is already listed in The behavior of a node processing a packet containing both a Routing
P1.REQUEST.Address[], then discard the packet. DONE. Header and a Route Request Destination option is unspecified.
Packets SHOULD NOT contain both a Routing Header and a Route Request
Destination option. [This is not exactly true: A Route Request
option appearing in the second Destination Options header that IPv6
allows after the Routing Header would probably do-what-you-mean,
though we have not triple-checked it yet. Namely, it would allow the
originator of a route discovery to unicast the request to some other
node, where it would be released and begin the flood fill. We call
this a Route Request Blossom since the unicast portion of the path
looks like a stem on the blossoming flood-fill of the request.]
4. If P1.REQUEST.Target_Address matches the home address of Packets containing a Route Request Destination option SHOULD NOT be
this node, then this packet contains a complete source route retransmitted, SHOULD NOT request an explicit DSR Acknowledgment by
setting the R bit, SHOULD NOT expect a passive acknowledgment, and
SHOULD NOT be placed in the Retransmission Buffer. The repeated
transmission of packets containing a Route Request Destination option
is controlled solely by the logic described in this section.
7.4.2. Processing a Route Request Option
When a node A receives a packet containing a Route Request option,
the Route Request option is processed as follows:
1. If Request.Target_Address matches the home address of this node,
then the Route Request option contains a complete source route
describing the path from the initiator of the Route Request to describing the path from the initiator of the Route Request to
this node. this node.
(a) Send a Route Reply as described in Section 6.1.3. (a) Send a Route Reply as described in Section 7.4.4.
(b) If P1.REQUEST.Next_Header indicates No Next Header, DONE. (b) Continue processing the packet in accordance with the Next
Header value contained in the Destination Option extension
header. DONE.
(c) Otherwise, swap P1.REQUEST.Target_Address and 2. Otherwise, if the combination (IP.Source_Address,
P1.Source_Address and pass the packet up the protocol Request.Identification) is found in the Route Request
stack. DONE. Table, then discard the packet, since this is a copy of a
recently seen Route Request. DONE.
5. Set P1.REQUEST.Address[n+1] = home address of this node. 3. Otherwise, if Request.Target_Address is a multicast address then:
Re-broadcast the Route Request packet jittered by T milliseconds,
where T is a uniformly distributed, random number between 0 and (a) If node A is a member of the multicast group indicated by
Request.Target_Address, then create a copy of the packet,
setting IP.Destination_Address = REQUEST.Target_Address, and
continue processing the copy of the packet in accordance with
the Next Header field of the Destination option.
(b) If IP.TTL is non-zero, decrement IP.TTL, and retransmit the
packet. DONE.
(c) Otherwise, discard the packet. DONE.
4. Otherwise, if the home address of node A is already listed in
the Route Request (IP.Source_Address or Request.Address[]), then
discard the packet. DONE.
5. Let
m = number of addresses currently in the Route Request option
n = m + 1
6. Otherwise, append the home address of node A to the Route Request
option (Request.Address[n]).
7. Set Request.IN_Index[n] = index of interface packet was received
on.
8. If a source route to Request.Target_Address is found in our Route
Cache and the rules of Section 7.4.3 permit it, return a Cached
Route Reply as described in Section 7.4.3. DONE.
9. Otherwise, for each interface on which the node is configured to
participate in a DSR ad hoc network:
(a) Make a copy of the packet containing the Route Request.
(b) Set Request.OUT_Index[n+1] = index of the interface.
(c) If the outgoing interface is different from the incoming
interface, then set the C bit on both Request.OUT_Index[n+1]
and Request.IN_Index[n]
(d) Link-layer re-broadcast the packet containing the Route
Request on the interface jittered by T milliseconds, where
T is a uniformly distributed, random number between 0 and
BROADCAST_JITTER. DONE. BROADCAST_JITTER. DONE.
6.1.3. Originating a Route Reply 7.4.3. Generating Route Replies using the Route Cache
Let P1 be the received packet containing a Route Request option. Let A node SHOULD use its Route Cache to avoid propagating a Route
P2 be a packet containing a corresponding Route Reply. A Route Reply Request packet received from another node. In particular, suppose a
is transmitted in response to a Route Request as follows: node receives a Route Request packet for which it is not the target
and which it does not discard based on the logic of Section 7.4.2.
If the node has a Route Cache entry for the target of the Request,
it SHOULD append this cached route to the accumulated route record
in the packet and return this route in a Route Reply packet to
the initiator without propagating (re-broadcasting) the Route
Request. Thus, for example, if node F in the example network shown
in Figure 7.4.3 needs to send a packet to node D, it will initiate
a Route Discovery and broadcast a Route Request packet. If this
broadcast is received by node A, node A can simply return a Route
Reply packet to F containing the complete route to D consisting of
the sequence of hops: A, B, C, and D.
1. If P1.REQUEST.Address[] does not contain any hops, then this node Before transmitting a Route Reply packet that was generated using
is only a single hop from the originator of the Route Request. information from its Route Cache, a node MUST verify that:
Build a Route Replay packet as follows:
P2.Destination_Address = P1.Source_Address 1. The resulting route contains no loops.
P2.Source_Address = P1.REQUEST.Target_Address
GOTO 3. 2. The node issuing the Route Reply is listed in the route that it
specifies in its Reply. This increases the probability that the
route is valid, since the node in question should have received
a Route Error if this route stopped working. Additionally, this
requirement means that a Route Error traversing the route will
pass through the node that issued the Reply based on stale cache
data, which is critical for ensuring stale data is removed from
caches in a timely manner. Without this requirement, the next
Route Discovery initiated by the original requester might also be
contaminated by a Route Reply from this node containing the same
stale route.
7.4.4. Originating a Route Reply
Let REQPacket denote a packet received by node A that
contains a Route Request option which lists node A as the
REQPacket.Request.Target_Address. Let REPPacket be a packet
transmitted by node A that contains a corresponding Route Reply. The
Route Reply option transmitted in response to a Route Request MUST be
initialized as follows:
B->C->D
+---+ +---+ +---+ +---+
| A |---->| B |---->| C |---->| D |
+---+ +---+ +---+ +---+
+---+
| F | +---+
+---+ | E |
+---+
Figure 1: An example network where A knows a
route to D via B and C.
1. If REQPacket.Request.Address[] does not contain any hops, then
node A is only a single hop from the originator of the Route
Request. Build a Route Reply packet as follows:
REPPacket.IP.Source_Address = REQPacket.Request.Target_Address
REPPacket.Reply.Target = REQPacket.IP.Source_Address
REPPacket.Reply.OUT_Index[1] = REQPacket.Request.OUT_index[1]
REPPacket.Reply.OUT_C_bit[1] = REQPacket.Request.OUT_C_bit[1]
REPPacket.Reply.Address[1] = The home address of node A
GOTO step 3.
2. Otherwise, build a Route Reply packet as follows: 2. Otherwise, build a Route Reply packet as follows:
P2.Destination_Address = P1.REQUEST.Address[1] REPPacket.IP.Source_Address = The home address of node A
P2.Source_Address = P1.REQUEST.Target_Address REPPacket.Reply.Target = REQPacket.IP.Source_Address
P2.REPLY.Address[1..n] = P1.REQUEST.Address[1..n] REPPacket.Reply.OUT_Index[1..n]= REQPacket.Request.OUT_index[1..n]
REPPacket.Reply.OUT_C_bit[1..n]= REQPacket.Request.OUT_C_bit[1..n]
REPPacket.Reply.Address[1..n] = REQPacket.Request.Address[1..n]
3. Transmit the Route Reply jittered by T milliseconds, where 3. Send the Route Reply jittered by T milliseconds, where T
T is a uniformly distributed, random number between 0 and is a uniformly distributed random number between 0 and
BROADCAST_JITTER. DONE. BROADCAST_JITTER. DONE.
If sending a Route Reply packet to the originator of the Route If sending a Route Reply packet to the originator of the Route
Request requires performing a Route Discovery, the Route Reply Request requires performing a Route Discovery, the Route Reply
destination option MUST be piggybacked on the packet that contains hop-by-hop option MUST be piggybacked on the packet that contains the
the Route Request. This prevents a loop wherein the target of the Route Request. This prevents a loop wherein the target of the new
Route Request (which was itself the originator of the original Route Route Request (which was itself the originator of the original Route
Request) must do another Route Request in order to return its Route Request) must do another Route Request in order to return its Route
Reply. Reply.
If sending the Route Reply to the originator of the Route Request If sending the Route Reply to the originator of the Route Request
does not require performing Route Discovery, nodes SHOULD send a does not require performing Route Discovery, a node SHOULD send a
unicast Route Reply in response to every Route Request targeted at unicast Route Reply in response to every Route Request targeted at
them. it.
6.1.4. Processing a Route Reply Option 7.4.5. Processing a Route Reply Option
Upon receipt of a Route Reply, a node should extract the source route Upon receipt of a Route Reply, a node should extract the source route
(Address[1..n] + Target Address) and insert this route into its Route (Target_Address, OUT_Index[1]:Address[1], .. OUT_Index[n]:Address[n]
Cache. Any packets in the Send Buffer that are addressed to Target ) and insert this route into its Route Cache. All the packets in the
Address SHOULD be processed. Send Buffer SHOULD be checked to see whether the information in the
Reply allows them to be sent immediately.
6.2. Route Maintenance 7.5. Route Maintenance
6.2.1. Originating a Route Error Route Maintenance requires that whenever a node transmits a data
packet, a Route Reply, or a Route Error, it must verify that the next
hop (indicated by the Destination IP Address) correctly receives the
packet.
If while forwarding a packet with a Routing Header, the next hop If the sender cannot verify that the next hop received the packet, it
specified in the source route is found to be unreachable, a Route MUST decide that its link to the next hop is broken and MUST send a
Error packet (Section 5.1.3) MUST be returned to the originator Route Error to the node responsible for generating the Routing Header
(Address[1]) of the packet. that contains the broken link (Section 7.5.3).
The forwarding node SHOULD consider the next hop to be unreachable if The following ways may be used to verify that the next hop correctly
any of the following conditions occurs: received a packet:
- The failure to receive a passive acknowledgment when such passive - The receipt of a passive acknowledgment (Section 7.5.1).
acknowledgments had been received previously.
- The failure to receive an explicitly requested acknowledgment - The receipt of an explicitly requested acknowledgment
after MAX_EXPLICIT_REXMIT retransmissions. (Section 7.5.1).
- In link layers providing retransmissions and acknowledgments - By the presence of positive feedback from the link layer
(e.g., 802.11), a signal from the link layer that it is unable to indicating that the packet was acknowledged by the next hop
deliver the packet. (Section 7.5.2).
6.2.2. Processing a Route Error Option - By the absence of explicit failure notification from the link
layer that provides reliable hop-by-hop delivery such as MACAW or
802.11 (Section 7.5.2).
Upon receipt of a Route Error via any mechanism, a node SHOULD remove Nodes MUST NOT perform Route Maintenance for packets containing a
any route from its Route Cache that uses the hop (From Hop Address, Route Request option or packets containing only an Acknowledgment
Next Hop Address). option. Sending Acknowledgments for packets containing only
an Acknowledgment option would create an infinite loop whereby
acknowledgments would be sent for acknowledgments. Acknowledgments
should be always sent for packets containing a Routing Header with
the R bit set (e.g., packets which contain only an Acknowledgment
and a Routing Header for which the last forwarding hop requires an
explicit acknowledgment of receipt by the final destination).
When the Route Error is returned to the Originator Address, the 7.5.1. Using Network-Layer Acknowledgments
originator must verify that the source route in the Route Error
packet (From Hop Address...Originator Address) includes the same
hops as the working prefix of the original packet's source route
(Originator Address...From Hop Address). If any hop listed in the
working prefix is not included in the Route Error's source route,
then the originator must transmit the Route Error back along the
working prefix (Originator Address...From Hop Address) so that each
node along the working prefix will remove the invalid route from its
Route Cache.
If the node processing a Route Error option discovers its home For link layers that do not provide explicit failure notification,
address equals the Router Error's Originator Address and the packet the following steps SHOULD be used by a node A to perform Route
contains an additional nested Route Error, the node MUST perform the Maintenance.
following steps:
1. Remove the Route Error being processed from the packet. When receiving a packet:
2. Copy the Originator Address from the next nested Route Error to - If the packet contains a Routing Header with the R bit set, send
the IP destination field of the packet. an explicit acknowledgment as described in Section 7.3.
3. Attach a source route and send the packet to the IP destination, - If the packet does not contain a Routing Header, the node MUST
performing Route Discovery if needed. transmit a packet containing the DSR Acknowledgment option
to the previous hop as indicated by the IP.Source_Address.
Since the receiving node is the final destination, there
will be no opportunity for the originator to obtain a
passive acknowledgment, and the receiving node must infer the
originator's request for an explicit acknowledgment.
6.2.3. Processing a DSR Acknowledgment Option When sending a packet:
Upon receipt of a DSR Acknowledgment, a node should remove any packet 1. Before sending a packet, insert a copy of the packet into the
in its Retransmission Buffer matching the (Address, Identification) Retransmission Buffer and update the information maintained about
pair found in the Acknowledgment option. If no match is found, the this packet in the Retransmission Buffer.
Acknowledgment should be silently discarded.
[I'm supposed to say something intelligent here, but I can't remember 2. If after processing the Routing Header, RH.Segments_Left is equal
what... -josh] to 0, then node A MUST set the Acknowledgment Request (R) bit in
the Routing Header before transmitting the packet over its final
hop.
6.3. Processing a Routing Header 3. If after processing the Routing Header and copying
RH.Address[n] to IP.Destination_Address, node A determines that
RH.OUT_C_bit[n+1] is set, then node A MUST set the Acknowledgment
Request (R) bit in the Routing Header before transmitting the
packet (since the C bit was set during Route Discovery by the
node now listed as the IP.Destination_Address to indicate that
it will propagate the packet out a different interface, and that
node A will not receive a passive acknowledgment).
A DSR Routing Header should be processed in accordance with the steps 4. Set the retransmission timer for the packet in the Retransmission
outlined for Routing Headers in [4]. The Routing Header is only Buffer.
processed by the node whose address appears as the IP destination
of the packet. A few additional rules apply to processing the type
specific data of a DSR Source Route:
1. The interface used to transmit the packet MUST be the interface 5. Transmit the packet.
denoted by Index[n] where Address[n] is the home address of this
6. If a passive or explicit acknowledgment is received before the
retransmission timer expires, then remove the packet from the
Retransmission Buffer and disable the retransmission timer.
DONE.
7. Otherwise, when the Retransmission Timer expires, remove the
packet from the Retransmission Buffer.
8. If DSR_MAXRXTSHIFT transmissions have been done, then attempt
to salvage the packet (Section 7.5.5). Also, generate a Route
Error. DONE.
9. GOTO step 1.
7.5.2. Using Link Layer Acknowledgments
If explicit failure notifications are provided by the link layer,
then all packets are assumed to be correctly received by the next hop
and a Route Error is sent only when a explicit failure notification
is made from the link layer.
Nodes receiving a packet without a Routing Header do not need to send
an explicit Acknowledgment to the packet's originator, since the
link layer will notify the originator if the packet was not received
properly.
7.5.3. Originating a Route Error
If the next hop of a packet is found to be unreachable as described
in Section 7.5, a Route Error packet (Section 6.2.2) MUST be returned
to the node whose cache generated the information used to route the
packet.
When a node A generates a Route Error for packet P, it MUST
initialize the fields in the Route Error as follows:
Error.Source_Address = Home address of node A
Error.Unreachable_Address = Home address of the unreachable node
- If the packet contains a DSR Routing Header and the S bit is NOT
set, the packet has been forwarded without the need for salvaging
up to this point.
Error.Destination_Address = P.IP.Source_Address
- Otherwise, if the packet contains a DSR Routing Header and the S
bit IS set, the packet has been salvaged by an intermediate node,
and thus this Routing Header was placed there by the salvaging
node. node.
2. If the Acknowledgment Request (R) bit is set, the node MUST Error.Destination_Address = P.RoutingHeader.Address[1]
create and transmit a packet containing the DSR Acknowledgment
option to the IP Source of the packet, performing Route Discovery
if necessary.
3. If the node chooses to set the Acknowledgment Request (R) bit in - Otherwise, if the packet does not contain a DSR Routing Header,
the packet when it forwards it, it must first make a copy of the the packet must have been originated by this node A.
packet and insert this copy into its Retransmission Buffer.
4. If a node finds the next hop in the Routing Header to be Error.Destination_Address = Home address of node A
unreachable, it MUST send a Route Error packet to the originator
of the packet, denoted by ROUTING.Address[1].
7. Optimizations Send the packet containing the Route Error to Error.Destination_Address,
performing Route Discovery if necessary.
As an optimization, Route Errors that are discovered by the
packet's originator (such that Error.Source_Address is equal to
Error.Destination_Address) SHOULD be processed internally. Such
processing should invoke all the steps that would be taken if a Route
Error option was created, transmitted, received, and processed,
but an actual packet containing a Route Error option SHOULD NOT be
transmitted.
7.5.4. Processing a Route Error Option
Upon receipt of a Route Error via any mechanism, a node
SHOULD remove any route from its Route Cache that uses the hop
(Error.Source_Address, Error.Index to Error.Unreachable_Address).
This includes all Route Errors overheard, and those processed
internally as described in Section 7.5.3.
When the node identified by Error.Destination_Address receives
the Route Error, it SHOULD verify that the source route
responsible for delivering the Route Error includes the same
hops as the working prefix of the original packet's source route
(Error.Destination_Address to Error.Source_Address). If any
hop listed in the working prefix is not included in the Route
Error's source route, then the originator SHOULD forward the Route
Error back along the working prefix (Error.Destination_Address to
Error.Source_Address) so that each node along the working prefix will
remove the invalid route from its Route Cache.
If the node processing a Route Error option discovers its home
address is Error.Destination_Address and the packet contains
additional Route Error option(s) later on the inside of the Hop
by Hop options header, we call the additional Route Errors nested
Route Errors. The node MUST deliver the first nested Route Error
to Nested_Error.Destination_Address, performing Route Discovery if
needed. It does this by removing the Route Error option listing
itself as the Error.Destination_Address, finding the first nested
Route Error option, and originating the remaining packet to
Nested_Error.Destination_Address. This mechanism allows for the
proper handling of Route Errors that are discovered while delivering
a Route Error.
7.5.5. Salvaging a Packet
When node A attempts to salvage a packet originated at node S and
destined for node D, it MUST perform the following steps:
1. Generate and send a Route Error to A as explained in
Section 7.5.3.
2. Call Route_Cache.Get() to determine if it has a cached source
route to the packet's ultimate destination D (which is the last
Address listed in the Routing Header).
3. If node A does not have a cached route for node D, it MUST
discard the packet. DONE.
4. Otherwise, let Salvage_Address[1] through Salvage_Address[m] be
the sequence of hops returned from the Route Cache. Initialize
the following fields in the packet's header:
RT.Segments_Left = m - 2;
RT.S = 1
RT.Address[1] = Home address of Node A
RT.Address[2] = Salvage.Address[1]
...
RT.Address[n] = Salvage.Address[m]
The IP Source Address of the packet MUST remain unchanged. When the
Routing Header in the outgoing packet is processed, RT.Address[2],
will be copied to the IP Destination Address field.
8. Optimizations
A number of optimizations can be added to the basic operation of A number of optimizations can be added to the basic operation of
Route Discovery and route maintenance as described in Section 4.1 Route Discovery and Route Maintenance as described in Sections 7.4
that can reduce the number of overhead packets and improve the and 7.5 that can reduce the number of overhead packets and improve
average efficiency of the routes used on data packets. This section the average efficiency of the routes used on data packets. This
discusses some of those optimizations. section discusses some of those optimizations.
7.1. Leveraging the Route Cache 8.1. Leveraging the Route Cache
The data in a node's Route Cache may be stored in any format, but The data in a node's Route Cache may be stored in any format, but
the active routes in its cache form a tree of routes, rooted at the active routes in its cache form a tree of routes, rooted at
this node, to other nodes in the ad hoc network. For example, the this node, to other nodes in the ad hoc network. For example, the
illustration below shows an ad hoc network of six mobile nodes, in illustration below shows an ad hoc network of six mobile nodes, in
which mobile node A has earlier completed a Route Discovery for which mobile node A has earlier completed a Route Discovery for
mobile node D and has cached a route to D through B and C: mobile node D and has cached a route to D through B and C:
B->C->D B->C->D
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
skipping to change at page 24, line 40 skipping to change at page 35, line 40
+---+ +---+
Since nodes B and C are on the route to D, node A also learns the Since nodes B and C are on the route to D, node A also learns the
route to both of these nodes from its Route Discovery for D. If A route to both of these nodes from its Route Discovery for D. If A
later performs a Route Discovery and learns the route to E through B later performs a Route Discovery and learns the route to E through B
and C, it can represent this in its Route Cache with the addition of and C, it can represent this in its Route Cache with the addition of
the single new hop from C to E. If A then learns it can reach C in a the single new hop from C to E. If A then learns it can reach C in a
single hop (without needing to go through B), A SHOULD use this new single hop (without needing to go through B), A SHOULD use this new
route to C to also shorten the routes to D and E in its Route Cache. route to C to also shorten the routes to D and E in its Route Cache.
7.1.1. Promiscuous Learning of Source Routes 8.1.1. Promiscuous Learning of Source Routes
A node can add entries to its Route Cache any time it learns a
new route. In particular, when a node forwards a data packet as
an intermediate hop on the route in that packet, the forwarding
node is able to observe the entire route in the packet. Thus, for
example, when node B forwards packets from A to D, B SHOULD add the
route information from that packet to its own Route Cache. If a
node forwards a Route Reply packet, it SHOULD also add the route
information from the route record being returned in the Route Reply,
to its own Route Cache.
Finally, since all wireless network transmissions are inherently
broadcast, a node MAY configure its network interface into
promiscuous receive mode, and add to its Route Cache the route
information from any packet it can overhear.
7.1.2. Answering Route Requests using the Route Cache
A node SHOULD use its Route Cache to avoid propagating a Route
Request packet received from another node. In particular, suppose a
node receives a Route Request packet for which it is not the target
and which it does not discard on based on the logic of section 6.1.1.
If the node has a Route Cache entry for the target of the request,
it may append this cached route to the accumulated route record
in the packet, and may return this route in a Route Reply packet
to the initiator without propagating (re-broadcasting) the Route
Request. Thus, for example, if node F in the example network shown
in Section 7.1 needs to send a packet to node D, it will initiate
a Route Discovery and broadcast a Route Request packet. If this
broadcast is received by A, A can simply return a Route Reply packet
to F containing the complete route to D consisting of the sequence of
hops A, B, C, and D.
Before transmitting a Route Reply packet that was generated using
information from its Route Cache, a node MUST verify that:
1. The resulting route does not contain any loops.
2. The node issuing the Route Reply is listed in the route that it
is replying with. This increases the probability that the route
is valid, since the node in question should have received a Route
Error if this route stopped working.
7.2. Route Discovery Using Expanding Ring Search
The propagating nature of a basic Route Request packet means that
potentially every node in the ad hoc network will be disturbed
whenever one is originated. To reduce this network-wide cost, all
nodes SHOULD limit the maximum propagation of their Route Requests in
some way, and MAY use the following algorithm.
1. Whenever the backoff algorithm permits the initiation of a Route
Discovery, initially send a Route Request with a hop limit of one
(we refer to this as a non-propagating Route Request).
2. If no Route Reply is received from the non-propagating Route A node can add entries to its Route Cache any time it learns a new
Request after RING0_TIMEOUT seconds, send a new Route Request route. In particular, when a node forwards a data packet as an
with the hop limit set to MAX_ROUTE_LEN. intermediate hop on the route in that packet, the forwarding node is
able to observe the entire route in the packet. Thus, for example,
when any intermediate node B forwards packets from A to D, B SHOULD
add the source route information from that packet's Routing Header
to its own Route Cache. If a node forwards a Route Reply packet, it
SHOULD also add the source route information from the route record
being returned in the Route Reply, to its own Route Cache.
A single attempt at Route Discovery for destination node D may In addition, since all wireless network transmissions at the physical
therefore involve sending two Route Request packets. Nodes MUST layer are inherently broadcast, it may be possible for a node to
not backoff between the sending a Route Request with a hop limit of configure its network interface into promiscuous receive mode, such
one and the subsequent sending of Route Request with a hop limit of that the node is able to receive all packets without link layer
MAX_ROUTE_LEN. This procedure uses the hop limit on the Route Request address filtering. In this case, the node MAY add to its Route Cache
packet to inexpensively check if the target is currently within the route information from any packet it can overhear.
wireless transmitter range of the initiator, or if another node
within range has a Route Cache entry for this target (effectively
using the caches of this node's neighbors as an extension of its own
cache). Since the initial request is limited to one network hop, the
timeout period before sending the propagating request can be quite
small.
7.3. Preventing Route Reply Storms 8.2. Preventing Route Reply Storms
The ability for nodes to reply to a Route Request not targeted at The ability for nodes to reply to a Route Request not targeted at
them using their Route Caches can result in a Route Reply storm. If them by using their Route Caches can result in a Route Reply storm.
a node broadcasts a Route Request for a node that its neighbors have If a node broadcasts a Route Request for a node that its neighbors
in their Route Caches, each neighbor may attempt to send a Route have in their Route Caches, each neighbor may attempt to send a
Reply thereby wasting bandwidth and increasing the rate of collisions Route Reply, thereby wasting bandwidth and increasing the rate
in the area. For example, in the network shown in Section 7.1, if of collisions in the area. For example, in the network shown in
both A and B receive F's Route Request, they will both attempt to Section 8.1, if both node A and node B receive F's Route Request,
reply from their Route Caches. Both will send their replies at they will both attempt to reply from their Route Caches. Both will
about the same time since they receive the broadcast at about the send their Replies at about the same time since they receive the
same time. Particularly when more than the two mobile nodes in this broadcast at about the same time. Particularly when more than the
example are involved, these simultaneous replies from the mobile two mobile nodes in this example are involved, these simultaneous
nodes receiving the broadcast may create packet collisions among replies from the mobile nodes receiving the broadcast may create
some or all of these replies and may cause local congestion in the packet collisions among some or all of these replies and may cause
wireless network. In addition, it will often be the case that the local congestion in the wireless network. In addition, it will
different replies will indicate routes of different lengths. For often be the case that the different replies will indicate routes
example, A's reply will indicate a route to D that is one hop longer of different lengths. For example, A's Route Reply will indicate a
than that in B's reply. route to D that is one hop longer than that in B's reply.
For interfaces which can promiscuously listen to the channel, mobile For interfaces which can promiscuously listen to the channel, mobile
nodes SHOULD use the following algorithm to reduce the number of nodes SHOULD use the following algorithm to reduce the number of
simultaneous replies by slightly delaying their Route Reply: simultaneous replies by slightly delaying their Route Reply:
1. Pick a delay period 1. Pick a delay period
d = H * (h - 1 + r) d = H * (h - 1 + r)
where h is the length in number of network hops for the route to where h is the length in number of network hops for the route
be returned in this node's reply, r is a random number between 0 to be returned in this node's Route Reply, r is a random number
and 1, and H is a small constant delay to be introduced per hop. between 0 and 1, and H is a small constant delay to be introduced
per hop.
2. Delay transmitting the Route Reply from this node for a period 2. Delay transmitting the Route Reply from this node for a period
of d. of d.
3. Within the delay period, promiscuously receive all packets at 3. Within the delay period, promiscuously receive all packets at
this node. If a packet is received by this node during the delay this node. If a packet is received by this node during the delay
period that is addressed to the target of this Route Discovery period that is addressed to the target of this Route Discovery
(the target is the final destination address for the packet, (the target is the final destination address for the packet,
through any sequence of intermediate hops), and if the length of through any sequence of intermediate hops), and if the length of
the route on this packet is less than h, then cancel the delay the route on this packet is less than h, then cancel the delay
and do not transmit the Route Reply from this node; this node timer and do not transmit the Route Reply from this node; this
may infer that the initiator of this Route Discovery has already node may infer that the initiator of this Route Discovery has
received a Route Reply, giving an equal or better route. already received a Route Reply, giving an equally good or better
route.
7.4. Piggybacking on Route Discoveries 8.3. Piggybacking on Route Discoveries
As described in Section 4.1, when one node needs to send a packet As described in Section 4.1, when one node needs to send a packet
to another, if the sender does not have a Route Cached to the to another, if the sender does not have a route cached to the
destination node, it must initiate a Route Discovery, either destination node, it must initiate a Route Discovery, buffering the
buffering the original packet until the Route Reply is returned, or original packet until the Route Reply is returned. The delay for
discarding it and relying on a higher-layer protocol to retransmit Route Discovery and the total number of packets transmitted can be
it if needed. The delay for Route Discovery and the total number reduced by allowing data to be piggybacked on Route Request packets.
of packets transmitted can be reduced by allowing data to be Since some Route Requests may be propagated widely within the ad hoc
piggybacked on Route Request packets. Since some Route Requests may network, though, the amount of data piggybacked must be limited. We
be propagated widely within the ad hoc network, though, the amount currently use piggybacking when sending a Route Reply or a Route
of data piggybacked must be limited. We currently use piggybacking Error packet, since both are naturally small in size. Small data
when sending a Route Reply or a Route Error packet, since both are packets such as the initial SYN packet opening a TCP connection [13]
naturally small in size, and small data packets such as the initial could easily be piggybacked.
SYN packet opening a TCP connection [13] could easily be piggybacked.
One problem, however, arises when piggybacking on Route Request One problem, however, arises when piggybacking on Route Request
packets. If a Route Request is received by a node that replies packets. If a Route Request is received by a node that replies
to the request based on its Route Cache without propagating the to the request based on its Route Cache without propagating the
request (Section 7.1), the piggybacked data will be lost if the node Request (Section 8.1), the piggybacked data will be lost if the node
simply discards the Route Request. In this case, before discarding simply discards the Route Request. In this case, before discarding
the packet, the node must construct a new packet containing the the packet, the node must construct a new packet containing the
piggybacked data from the Route Request packet. The source route piggybacked data from the Route Request packet. The source route
in this packet MUST be constructed to appear as if the new packet in this packet MUST be constructed to appear as if the new packet
had been sent by the initiator of the Route Discovery and had been had been sent by the initiator of the Route Discovery and had been
forwarded normally to this node. Hence, the first portion of the forwarded normally to this node. Hence, the first portion of the
route is taken from the accumulated route record in the Route Request route is taken from the accumulated route record in the Route Request
packet and the remainder of the route is taken from this node's Route packet and the remainder of the route is taken from this node's Route
Cache. The sender address in the packet should also be set to the Cache. The sender address in the packet MUST also be set to the
initiator of the Route Discovery. Since the replying node will be initiator of the Route Discovery. Since the replying node will be
unable to correctly recompute an Authentication header for the split unable to correctly recompute an Authentication header for the split
off piggybacked data, data covered by an Authentication header SHOULD off piggybacked data, data covered by an Authentication header SHOULD
NOT be piggybacked on Route Request packets. NOT be piggybacked on Route Request packets.
7.5. Discovering Shorter Routes 8.4. Discovering Shorter Routes
Once a route between a packet source and a destination has been Once a route between a packet source and a destination has been
discovered, the basic DSR protocol MAY continue to use that route for discovered, the basic DSR protocol MAY continue to use that route
all traffic from the source to the destination, even if the nodes for all traffic from the source to the destination as long as
move such that a shorter route becomes possible. In many cases, the it continues to work, even if the nodes move such that a shorter
basic route maintenance procedure will discover the shorter route, route becomes possible. In many cases, the basic Route Maintenance
since if a node moves enough to create a shorter route, it will procedure will discover the shorter route, since if a node moves
likely also move out of transmission range of at least one hop on the enough to create a shorter route, it will likely also move out of
existing route. transmission range of at least one hop on the existing route.
When operating in promiscuous receive mode, a node SHOULD use the Furthermore, when a data packet is received as the result of
following algorithm to process a received packet. Whenever possible, operating in promiscuous receive mode, the node checks if the Routing
this algorithm shortens routes that already exist in the Route Cache. Header packet contains its address in the unprocessed portion of the
source route (Address[NumAddrs - SegLft] to Address[NumAddrs]). If
so, the node knows that packet could bypass the unprocessed hops
preceding it in the source route. The node then sends what is called
a gratuitous Route Reply message to the packet's source, giving it
the shorter route without these hops.
The following algorithm describes how a node A should process packets
with an IP.Destination_Address not addressed to A or the IP broadcast
address or a multicast address that are received as a result of A
being in promiscuous receive mode:
1. If the packet is not a data packet containing a Routing Header, 1. If the packet is not a data packet containing a Routing Header,
drop the packet. DONE. drop the packet. DONE.
2. If the IP destination is the home address of this node, then 2. If the home address of this node does not appear in the portion
follow the normal steps to process the packet. DONE.
3. If the home address of this node does not appear in the portion
of the source route that has not yet been processed (indicated by of the source route that has not yet been processed (indicated by
Segments Left), then drop the packet. DONE. Segments Left), then drop the packet. DONE.
4. The node S indicated by the Source Address field in the IP header 3. Otherwise, the node B that just transmitted the packet (indicated
can communicated directly with this node N. Create a Route Reply. by Address[NumAddrs - SegLft - 1]) can communicate directly with
The Route Reply MUST list the entire source routing contained in this node A. Create a Route Reply. The Route Reply MUST list
the received packet with the exception of the intermediate nodes the entire source route contained in the received packet with the
between node S and node N. exception of the intermediate nodes between node B and node A.
7.6. Rate Limiting the Route Discovery Process 4. Send this gratuitous Route Reply to the node listed as the
IP.Source_Address of the received packet. If Route Discovery
is required it MAY be initiated, or the gratuitous Route Reply
packet MAY be dropped.
8.5. Rate Limiting the Route Discovery Process
One common error condition that must be handled in an ad hoc network One common error condition that must be handled in an ad hoc network
is the case in which the network effectively becomes partitioned. is the case in which the network effectively becomes partitioned.
That is, two nodes that wish to communicate are not within That is, two nodes that wish to communicate are not within
transmission range of each other, and there are not enough other transmission range of each other, and there are not enough other
mobile nodes between them to form a sequence of hops through which mobile nodes between them to form a sequence of hops through which
they can forward packets. If a new Route Discovery was initiated they can forward packets. If a new Route Discovery was initiated
for each packet sent by a node in this situation, a large number of for each packet sent by a node in this situation, a large number of
unproductive Route Request packets would be propagated throughout the unproductive Route Request packets would be propagated throughout the
subset of the ad hoc network reachable from this node. In order to subset of the ad hoc network reachable from this node. In order to
reduce the overhead from such route discoveries, we use exponential reduce the overhead from such Route Discoveries, we use exponential
backoff to limit the rate at which new route discoveries may be back-off to limit the rate at which new Route Discoveries may be
initiated from any node for the same target. If the node attempts to initiated from any node for the same target. If the node attempts to
send additional data packets to this same node more frequently than send additional data packets to this same node more frequently than
this limit, the subsequent packets SHOULD be buffered in the Send this limit, the subsequent packets SHOULD be buffered in the Send
Buffer until a Route Reply is received, but it MUST NOT initiate a Buffer until a Route Reply is received, but it MUST NOT initiate a
new Route Discovery until the minimum allowable interval between new new Route Discovery until the minimum allowable interval between new
route discoveries for this target has been reached. This limitation Route Discoveries for this target has been reached. This limitation
on the maximum rate of route discoveries for the same target is on the maximum rate of Route Discoveries for the same target is
similar to the mechanism required by Internet nodes to limit the rate similar to the mechanism required by Internet nodes to limit the rate
at which ARP requests are sent to any single IP address [1]. at which ARP requests are sent to any single IP address [1].
7.7. Improved Handling of Route Errors 8.6. Improved Handling of Route Errors
All nodes SHOULD process all of the Route Error messages they All nodes SHOULD process all of the Route Error messages they
receive, regardless of whether the node is the destination of receive, regardless of whether the node is the destination of
the Route Error, is forwarding the Route Error, or promiscuously the Route Error, is forwarding the Route Error, or promiscuously
overhears the Route Error. overhears the Route Error.
Since a Route Error packet names both ends of the hop that is no Since a Route Error packet names both ends of the hop that is no
longer valid, any of the nodes receiving the error packet may update longer valid, any of the nodes receiving the error packet may update
their Route Caches to reflect the fact that the two nodes indicated their Route Caches to reflect the fact that the two nodes indicated
in the packet can no longer directly communicate. A node receiving in the packet can no longer directly communicate. A node receiving
a Route Error packet simply searches its Route Cache for any routes a Route Error packet simply searches its Route Cache for any routes
using this hop. For each such route found, the route is truncated at using this hop. For each such route found, the route is effectively
this hop. All nodes on the route before this hop are still reachable truncated at this hop. All nodes on the route before this hop are
on this route, but subsequent nodes are not. still reachable on this route, but subsequent nodes are not.
An experimental optimization to improve the handling of errors is An experimental optimization to improve the handling of errors is
to support the caching of "negative" information in a node's Route to support the caching of "negative" information in a node's Route
Cache. The goal of negative information is to record that a given Cache. The goal of negative information is to record that a given
route was tried and found not to work, so that if the same route route was tried and found not to work, so that if the same route
is discovered again shortly after the failure, the Route Cache can is discovered again shortly after the failure, the Route Cache can
ignore or downgrade the metric of the failed route. ignore or downgrade the metric of the failed route.
We have not currently included this caching of negative information We have not currently included this caching of negative information
in our simulations, since it appears to be unnecessary if nodes also in our simulations, since it appears to be unnecessary if nodes also
promiscuously receive Route Error packets. promiscuously receive Route Error packets.
8. Constants 9. Constants
BROADCAST_JITTER 10 milliseconds BROADCAST_JITTER 10 milliseconds
ID_FIFO_SIZE 8 identifiers MAX_ROUTE_LEN 15 nodes
INVALID_INTERFACE_INDEX 0xFF Interface Indexes
IF_INDEX_INVALID 0x7F
IF_INDEX_MA 0x7E
IF_INDEX_ROUTER 0x7D
MAX_EXPLICIT_REXMIT 3 attempts Route Cache
ROUTE_CACHE_TIMEOUT 300 seconds
MAX_RTDISCOV_INTERVAL 120 seconds Send Buffer
SEND_BUFFER_TIMEOUT 30 seconds
MAX_ROUTE_LEN 15 nodes Request Table
MAX_REQUEST_ENTRIES 32 nodes
MAX_REQUEST_IDS 8 identifiers
MAX_REQUEST_REXMT 16 retransmissions
MAX_REQUEST_PERIOD 10 seconds
REQUEST_PERIOD 500 milliseconds
RING0_REQUEST_TIMEOUT 30 milliseconds
RING0_TIMEOUT 30 milliseconds Retransmission Buffer
DSR_RXMT_BUFFER_SIZE 50 packets
ROUTE_CACHE_TIMEOUT 300 seconds Retransmission Timer
DSR_MAXRXTSHIFT 2
SEND_BUFFER_TIMEOUT 30 seconds 10. IANA Considerations
9. IANA Considerations This document proposes the use of the Destination Options header and
the Hop-by-Hop Options header, originally defined for IPv6, in IPv4.
The Next Header values indicating these two extension headers thus
must be reserved within the IPv4 Protocol number space.
This document defines four new types of IPv6 destination option, each Furthermore, this document defines four new types of destination
of which must be assigned an Option Type value: options, each of which must be assigned an Option Type value:
- The DSR Route Request option, described in Section 5.1.1 - The DSR Route Request option, described in Section 6.1.1
- The DSR Route Reply option, described in Section 5.1.2 - The DSR Route Reply option, described in Section 6.2.1
- The DSR Route Error option, described in Section 5.1.3 - The DSR Route Error option, described in Section 6.2.2
- The DSR Acknowledgment option, described in Section 5.1.4 - The DSR Acknowledgment option, described in Section 6.2.3
DSR also requires a routing header Routing Type be allocated for the DSR also requires a routing header Routing Type be allocated for the
DSR Source Route defined in section 5.2. DSR Source Route defined in Section 6.3.
In IPv4, we require two new protocol numbers be issued to identify In IPv4, we require two new protocol numbers be issued to identify
the next header as either an IPv6-style destination option, or an the next header as either an IPv6-style destination option, or an
IPv6-style routing header. Other protocols can make use of these IPv6-style routing header. Other protocols can make use of these
protocol numbers as nodes that support them will processes any protocol numbers as nodes that support them will processes any
included destination options or routing headers according to the included destination options or routing headers according to the
normal IPv6 semantics. normal IPv6 semantics.
10. Security Considerations 11. Security Considerations
This document does not specifically address security concerns. This This document does not specifically address security concerns. This
document does assume that all nodes participating in the DSR protocol document does assume that all nodes participating in the DSR protocol
do so in good faith and with out malicious intent to corrupt the do so in good faith and with out malicious intent to corrupt the
routing ability of the network. In mission-oriented environments routing ability of the network. In mission-oriented environments
where all the nodes participating in the DSR protocol share a where all the nodes participating in the DSR protocol share a
common goal that motivates their participation in the protocol, the common goal that motivates their participation in the protocol, the
communications between the nodes can be encrypted at the physical communications between the nodes can be encrypted at the physical
channel or link layer to prevent attack by outsiders. channel or link layer to prevent attack by outsiders.
Location of DSR Functions in the ISO Model Location of DSR Functions in the ISO Reference Model
When designing DSR, we had to determine at what level within the When designing DSR, we had to determine at what level within the
protocol hierarchy to implement source routing. We considered two protocol hierarchy to implement source routing. We considered two
different options: routing at the link layer (ISO layer 2) and different options: routing at the link layer (ISO layer 2) and
routing at the network layer (ISO layer 3). Originally, we opted to routing at the network layer (ISO layer 3). Originally, we opted to
route at the link layer for the following reasons: route at the link layer for the following reasons:
- Pragmatically, running the DSR protocol at the link layer - Pragmatically, running the DSR protocol at the link layer
maximizes the number of mobile nodes that can participate in maximizes the number of mobile nodes that can participate in
ad hoc networks. For example, the protocol can route equally ad hoc networks. For example, the protocol can route equally
well between IP [12], IPv6 [4], and IPX [5] nodes. well between IPv4 [12], IPv6 [4], and IPX [5] nodes.
- Historically, DSR grew from our contemplation of a multihop ARP - Historically, DSR grew from our contemplation of a multi-hop ARP
protocol [6, 7] and source routing bridges [10]. ARP [11] is a protocol [6, 7] and source routing bridges [10]. ARP [11] is a
layer 2protocol. layer 2protocol.
- Technically, we designed DSR to be simple enough that that it - Technically, we designed DSR to be simple enough that that it
could be implemented directly in network interface cards, well could be implemented directly in network interface cards, well
below the layer 3 software within a mobile node. We see great below the layer 3 software within a mobile node. We see great
potential for DSR running between clouds of mobile nodes around potential for DSR running between clouds of mobile nodes around
fixed base stations. DSR would act to transparently fill in the fixed base stations. DSR would act to transparently fill in the
coverage gaps between base stations. Mobile nodes that would coverage gaps between base stations. Mobile nodes that would
otherwise be unable to communicate with the base station due to otherwise be unable to communicate with the base station due to
factors such as distance, fading, or local interference sources factors such as distance, fading, or local interference sources
could then reach the base station through their peers. could then reach the base station through their peers.
Ultimately, however, we decided to design DSR as a layer 3 protocol Ultimately, however, we decided to specify DSR as a layer 3 protocol
since this is the only layer at which we could realistically support since this is the only layer at which we could realistically support
nodes with multiple interfaces of different types. nodes with multiple interfaces of different types.
Implementation Status Implementation Status
We have implemented Dynamic Source Routing (DSR) under the We have implemented Dynamic Source Routing (DSR) under the
FreeBSD 2.2.2 operating system running on Intel x86 platforms. FreeBSD 2.2.7 operating system running on Intel x86 platforms.
FreeBSD is based on a variety of free software, including 4.4 BSD FreeBSD is based on a variety of free software, including 4.4 BSD
Lite from the University of California, Berkeley. Lite from the University of California, Berkeley.
Acknowledgments Acknowledgments
The protocol described in this draft has been designed within The protocol described in this draft has been designed within
the CMU Monarch Project, a research project at Carnegie Mellon the CMU Monarch Project, a research project at Carnegie Mellon
University which is developing adaptive networking protocols and University which is developing adaptive networking protocols and
protocol interfaces to allow truly seamless wireless and mobile host protocol interfaces to allow truly seamless wireless and mobile node
networking [8, 14]. The current members of the CMU Monarch Project networking [8, 14]. The current members of the CMU Monarch Project
include: include:
- Josh Broch - Josh Broch
- Yih-Chun Hu - Yih-Chun Hu
- Jorjeta Jetcheva - Jorjeta Jetcheva
- David B. Johnson - David B. Johnson
- David A. Maltz - Qifa Ke
Areas for Refinement
We are currently working to refine the DSR protocol in the following
ways:
- Improve the algorithms and data structures used by the Route
Cache. We currently represent the Route Cache as a directed
acyclic tree of paths branching out from a root that represents
the node owning the Route Cache. However, each source
route learned by the Route Cache effectively describes the
interconnectedness of all the hops listed on the route, and
can be treated as a type of partial information Link State
Packet as one would find in a Link State routing algorithm.
By generalizing the Route Cache to a graph of all known links
between all known nodes, it may be possible to better leverage
the information a node overhears.
- Support for better route selection. In order to select the
best source route to send a packet with, nodes need be able to
evaluate the costs/benefits of each of their cached routes to the
destination. If those routes involve forwarding through nodes
with more than one interface, some routes may be better suited to
the traffic type because the bandwidth/range/latency/error-rate
characteristics of of the interfaces used on those routes best
match the needs of the traffic type. The Route Request and Route
Reply option format must be extended to enable node to report
the properties of the interfaces on the route, as well as the
interface index used in basic DSR forwarding.
- Improved Route Discovery algorithms. We are investigating ways - David A. Maltz
to cancel a propagating Route Request if the target of the
request has already been found in another part of the network.
Similarly, we are studying various ring-search algorithms in case
a more sophisticated algorithm might perform better than the
2-step algorithm we currently use.
References References
[1] R. Braden, editor. Requirements for Internet Hosts -- [1] R. Braden, editor. Requirements for Internet Hosts --
Communication Layers. RFC 1122, October 1989. Communication Layers. RFC 1122, October 1989.
[2] Scott Bradner. Key words for use in RFCs to Indicate [2] Scott Bradner. Key words for use in RFCs to Indicate
Requirement Levels. RFC 2119, March 1997. Requirement Levels. RFC 2119, March 1997.
[3] Scott Corson and Joseph Macker. Mobile Ad Hoc Networking [3] Scott Corson and Joseph Macker. Mobile Ad Hoc Networking
skipping to change at page 39, line 5 skipping to change at page 47, line 8
for Transmission on Ethernet Hardware. RFC 826, November 1982. for Transmission on Ethernet Hardware. RFC 826, November 1982.
[12] J. Postel, editor. Internet Protocol. RFC 791, September 1981. [12] J. Postel, editor. Internet Protocol. RFC 791, September 1981.
[13] J. Postel, editor. Transmission Control Protocol. RFC 793, [13] J. Postel, editor. Transmission Control Protocol. RFC 793,
September 1981. September 1981.
[14] The CMU Monarch Project. http://www.monarch.cs.cmu.edu/. [14] The CMU Monarch Project. http://www.monarch.cs.cmu.edu/.
Computer Science Department, Carnegie Mellon University. Computer Science Department, Carnegie Mellon University.
[15] J. Reynolds and J. Postel. Assigned Numbers. RFC 1700, October
1994.
Chair's Address Chair's Address
The Working Group can be contacted via its current chairs: The Working Group can be contacted via its current chairs:
M. Scott Corson M. Scott Corson
Institute for Systems Research Institute for Systems Research
University of Maryland University of Maryland
College Park, MD 20742 College Park, MD 20742
USA USA
skipping to change at page 40, line 11 skipping to change at page 49, line 11
Phone: +1 202 767-2001 Phone: +1 202 767-2001
Email: macker@itd.nrl.navy.mil Email: macker@itd.nrl.navy.mil
Authors' Addresses Authors' Addresses
Questions about this document can also be directed to the authors: Questions about this document can also be directed to the authors:
Josh Broch Josh Broch
Carnegie Mellon University Carnegie Mellon University
Electrical and Computer Engineering Department Electrical and Computer Engineering
5000 Forbes Avenue 5000 Forbes Avenue
Pittsburgh, PA 15213-3891 Pittsburgh, PA 15213-3890
USA USA
Phone: +1 412 268-3056 Phone: +1 412 268-3056
Email: broch@andrew.cmu.edu Fax: +1 412 268-7196
Email: broch@cs.cmu.edu
David B. Johnson David B. Johnson
Carnegie Mellon University Carnegie Mellon University
Computer Science Department Computer Science Department
5000 Forbes Avenue 5000 Forbes Avenue
Pittsburgh, PA 15213-3891 Pittsburgh, PA 15213-3891
USA USA
Phone: +1 412 268-7399 Phone: +1 412 268-7399
Fax: +1 412 268-5576 Fax: +1 412 268-5576
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