Mobile Ad hoc Networks Working Group                          S. Ratliff
Group                                             Independent Consultant
Internet-Draft                                                  B. Berry                                                VT iDirect
Intended status: Standards Track                             G. Harrison                                B. Berry
Expires: April 2, August 31, 2015
                                                                 S. Jury
                                                           Cisco Systems
                                                          D. Satterwhite
                                                                Broadcom
                                                        October 24, 2014
                                                               R. Taylor
                                                  Airbus Defence & Space
                                                       February 27, 2015

                 Dynamic Link Exchange Protocol (DLEP)
                        draft-ietf-manet-dlep-07
                        draft-ietf-manet-dlep-08

Abstract

   When routing devices rely on modems to effect communications over
   wireless links, they need timely and accurate knowledge of the
   characteristics of the link (speed, state, etc.) in order to make
   forwarding decisions.  In mobile or other environments where these
   characteristics change frequently, manual configurations or the
   inference of state through routing or transport protocols does not
   allow the router to make the best decisions.  A bidirectional, event-
   driven communication channel between the router and the modem is
   necessary.

Status of this This Memo

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   This Internet-Draft will expire on August 14, 2014. 31, 2015.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1
     1.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . . .   8
   2.  Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   3. Mandatory Versus  Core Features and Optional Items . . . . . . . . . . . . . . . .  9
   4. Credits . . . . . . . . . . . . . . . . Extensions . . . . . . . . . . . .  10
   5. Metrics . . . . . . . . . . . . . . . . .
     3.1.  Negotiation of Optional Extensions  . . . . . . . . . . .  10
   6.
     3.2.  Protocol Extensions to DLEP  . . . . . . . . . . . . . . . . . . . . . . 11
     6.1 Protocol Extensions  .  10
     3.3.  Experimental Signals and Data Items . . . . . . . . . . .  11
   4.  Metrics . . . . . . . . 11
     6.2 Vendor Extensions . . . . . . . . . . . . . . . . . . .  11
     4.1.  Mandatory Metrics . . 11
     6.3 Experimental Extensions . . . . . . . . . . . . . . . . . . 11
   7.  12
   5.  Normal Session Flow . . . . . . . . . . . . . . . . . . . . .  12
     7.1
     5.1.  DLEP Router session flow - Discovery case . . . . . . . . . 12
     7.2  13
     5.2.  DLEP Router session flow - Configured case  . . . . . . . . . 12
     7.3  13
     5.3.  DLEP Modem session flow . . . . . . . . . . . . . . . . . . 13
     7.4  14
     5.4.  Common Session Flow . . . . . . . . . . . . . . . . . . . .  14
   8. Mandatory Signals and Data Items
   6.  DLEP Message Processing . . . . . . . . . . . . . . . . 14
   9. Generic DLEP Signal Definition . . .  15
     6.1.  DLEP Signal Header  . . . . . . . . . . . . . 16
   10. DLEP Data Items . . . . . .  16
     6.2.  DLEP Generic Data Item  . . . . . . . . . . . . . . . . .  16
     10.1
   7.  DLEP Version Signals  . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.2  DLEP Port
     7.1.  Peer Discovery Signal . . . . . . . . . . . . . . . . . .  17
     7.2.  Peer Offer Signal . . . . . . 18
     10.3  Peer Type . . . . . . . . . . . . . .  18
     7.3.  Peer Initialization Signal  . . . . . . . . . . 18
     10.4  MAC Address . . . . .  19
     7.4.  Peer Initialization ACK Signal  . . . . . . . . . . . . .  20
     7.5.  Peer Update Signal  . . . . . 19
     10.5  IPv4 Address . . . . . . . . . . . . . .  21
     7.6.  Peer Update ACK Signal  . . . . . . . . . 19
     10.6  IPv6 Address . . . . . . . .  22
     7.7.  Peer Termination Signal . . . . . . . . . . . . . . . 20
     10.7  Maximum Data Rate (Receive) . .  23
     7.8.  Peer Termination ACK Signal . . . . . . . . . . . . . 21
     10.8  Maximum Data Rate (Transmit) . .  23
     7.9.  Destination Up Signal . . . . . . . . . . . . . 22
     10.9  Current Data Rate (Receive) . . . . .  24
     7.10. Destination Up ACK Signal . . . . . . . . . . 22
     10.10  Current Data Rate (Transmit)  . . . . . . . .  25
     7.11. Destination Down Signal . . . . . . 23
     10.11  Latency . . . . . . . . . . .  26
     7.12. Destination Down ACK Signal . . . . . . . . . . . . . . 24
     10.12  Resources (Receive) .  26
     7.13. Destination Update Signal . . . . . . . . . . . . . . . .  26
     7.14. Heartbeat Signal  . . 25
     10.13  Resources (Transmit) . . . . . . . . . . . . . . . . . . 25
     10.14  Relative  28
     7.15. Link Quality (Receive) . . Characteristics Request Signal . . . . . . . . . . . 26
     10.15  Relative  28
     7.16. Link Quality (Transmit) Characteristics ACK Signal . . . . . . . . . . . . 27
     10.16  Status .  29
   8.  DLEP Data Items . . . . . . . . . . . . . . . . . . . . . . .  30
     8.1.  DLEP Version  . 27
     10.17  Heartbeat Interval . . . . . . . . . . . . . . . . . . . 28
     10.18  Link Characteristics ACK Timer . .  31
     8.2.  Status  . . . . . . . . . . . 28
     10.19  Credit Window Status . . . . . . . . . . . . . .  32
     8.3.  DLEP Port . . . . 29
     10.20  Credit Grant Request . . . . . . . . . . . . . . . . . . 30
     10.21  Credit Request . .  33
     8.4.  Peer Type . . . . . . . . . . . . . . . . . . . 31
     10.22  DLEP Optional Signals Supported . . . . .  33
     8.5.  Heartbeat Interval  . . . . . . . . 31
     10.23  DLEP Optional Data Items Supported . . . . . . . . . . . 32
     10.24  DLEP Vendor Extension  34
     8.6.  Extensions Supported  . . . . . . . . . . . . . . . . . . 33
     10.25  IPv4 Attached Subnet  35
     8.7.  Experimental Definition . . . . . . . . . . . . . . . . .  35
     8.8.  MAC Address . 33
     10.26  IPv6 Attached Subnet . . . . . . . . . . . . . . . . . . 34
   11. DLEP Protocol Signals . . . .  36
     8.9.  IPv4 Address  . . . . . . . . . . . . . . . . 35
     11.1  Signal TLV Values . . . . . .  37
     8.10. IPv6 Address  . . . . . . . . . . . . . . 35
     11.2 Peer Discovery Signal . . . . . . . .  37
     8.11. IPv4 Attached Subnet  . . . . . . . . . . . 36
     11.3 Peer Offer Signal . . . . . . .  38
     8.12. IPv6 Attached Subnet  . . . . . . . . . . . . . . 36
     11.4 Peer Initialization Signal . . . .  39
     8.13. Maximum Data Rate (Receive) . . . . . . . . . . . . 37
     11.5 Peer Initialization ACK Signal . . .  39
     8.14. Maximum Data Rate (Transmit)  . . . . . . . . . . . 37
     11.6 Peer Update Signal . . .  40
     8.15. Current Data Rate (Receive) . . . . . . . . . . . . . . .  41
     8.16. Current Data Rate (Transmit)  . . 38
     11.7 Peer Update ACK Signal . . . . . . . . . . . .  41
     8.17. Latency . . . . . . 39
     11.8 Peer Termination Signal . . . . . . . . . . . . . . . . . . 40
     11.9 Peer Termination ACK Signal .  42
     8.18. Resources (Receive) . . . . . . . . . . . . . . . 40
     11.10 Destination Up Signal . . . .  43
     8.19. Resources (Transmit)  . . . . . . . . . . . . . . 40
     11.11 Destination Up ACK Signal . . . .  43
     8.20. Relative Link Quality (Receive) . . . . . . . . . . . . 41
     11.12 Destination Down Signal .  44
     8.21. Relative Link Quality (Transmit)  . . . . . . . . . . . .  45
     8.22. Link Characteristics ACK Timer  . . . . 41
     11.13 Destination Down ACK Signal . . . . . . . . .  45
   9.  Credit-Windowing  . . . . . . 42
     11.14 Destination Update Signal . . . . . . . . . . . . . . . . 42
     11.15 Heartbeat Signal  46
     9.1.  Credit-Windowing Signals  . . . . . . . . . . . . . . . .  46
       9.1.1.  Destination Up Signal . . . . . 43
     11.16 Link Characteristics Request Signal . . . . . . . . . . . 43
     11.17 Link Characteristics  46
       9.1.2.  Destination Up ACK Signal . . . . . . . . . . . . . 44
   12.  Security Considerations . . .  47
       9.1.3.  Destination Update Signal . . . . . . . . . . . . . .  47
     9.2.  Credit-Windowing Data Items . . 45
   13.  IANA Considerations . . . . . . . . . . . . .  47
       9.2.1.  Credit Window Status  . . . . . . . . 45
     13.1  Registrations . . . . . . . .  47
       9.2.2.  Credit Grant  . . . . . . . . . . . . . . 45
     13.2  Expert Review: Evaluation Guidelines . . . . . .  48
       9.2.3.  Credit Request  . . . . . 45
     13.3  Signal TLV Type Registration . . . . . . . . . . . . . .  49
   10. Security Considerations . 45
     13.4  DLEP Data Item Registrations . . . . . . . . . . . . . . . 46
     13.5  DLEP Well-known Port . . .  50
   11. IANA Considerations . . . . . . . . . . . . . . . . 47
     13.6  DLEP Multicast Address . . . . .  50
     11.1.  Registrations  . . . . . . . . . . . . . 47
   14. Appendix A. . . . . . . . .  50
     11.2.  Expert Review: Evaluation Guidelines . . . . . . . . . .  51
     11.3.  Signal Type Registration . . . . . . . 47
     14.1  Peer Level Signal Flows . . . . . . . . .  51
     11.4.  DLEP Data Item Registrations . . . . . . . . 47
       14.1.1  Router Device Restarts Discovery . . . . . .  52
     11.5.  DLEP Status Code Registrations . . . . . 47
       14.1.2  Router Device Detects Peer Offer Timeout . . . . . . . 48
       14.1.3  Router Peer Offer Lost .  53
     11.6.  DLEP Extensions Registrations  . . . . . . . . . . . . .  53
     11.7.  DLEP Well-known Port . . 49
       14.1.4  Discovery Success . . . . . . . . . . . . . . . .  54
     11.8.  DLEP Multicast Address . . 49
       14.1.5  Router Detects a Heartbeat timeout . . . . . . . . . . 50
       14.1.6  Modem Detects a Heartbeat timeout . . . . .  54
   12. Acknowledgements  . . . . . 50
       14.1.7  Peer Terminate (from Modem) Lost . . . . . . . . . . . 51
       14.1.8  Peer Terminate (from Router) Lost . . . . . .  54
   13. References  . . . . 51
     14.2  Destination Specific Signal Flows . . . . . . . . . . . . 51
       14.2.1  Modem Destination Up Lost . . . . . . . . .  54
     13.1.  Normative References . . . . . 52
       14.2.2  Router Detects Duplicate Destination Ups . . . . . . . 52
       14.2.3  Destination Up, No Layer 3 Addresses . . . . . .  54
     13.2.  Informative References . . . 53
       14.2.4  Destination Up with IPv4, No IPv6 . . . . . . . . . . 53
       14.2.5  Destination Up with IPv4 and IPv6 . . . .  54
   Appendix A.  Peer Level Signal Flows  . . . . . . 53
       14.2.6  Destination Session Success . . . . . . . .  54
     A.1.  Router Device Restarts Discovery  . . . . . 54
   Acknowledgements . . . . . . .  54
     A.2.  Router Device Detects Peer Offer Timeout  . . . . . . . .  55
     A.3.  Router Peer Offer Lost  . . . . . . . . . . 54
   Normative References . . . . . . .  55
     A.4.  Discovery Success . . . . . . . . . . . . . . . . 55
   Informative References . . . .  56
     A.5.  Router Detects a Heartbeat timeout  . . . . . . . . . . .  57
     A.6.  Modem Detects a Heartbeat timeout . . . . . . . 55
   Author's Addresses . . . . .  57
     A.7.  Peer Terminate (from Modem) Lost  . . . . . . . . . . . .  58
     A.8.  Peer Terminate (from Router) Lost . . . . . . . 55 . . . . .  58
   Appendix B.  Destination Specific Signal Flows  . . . . . . . . .  59
     B.1.  Modem Destination Up Lost . . . . . . . . . . . . . . . .  59
     B.2.  Router Detects Duplicate Destination Ups  . . . . . . . .  59
     B.3.  Destination Up, No Layer 3 Addresses  . . . . . . . . . .  60
     B.4.  Destination Up with IPv4, No IPv6 . . . . . . . . . . . .  60
     B.5.  Destination Up with IPv4 and IPv6 . . . . . . . . . . . .  61
     B.6.  Destination Session Success . . . . . . . . . . . . . . .  61
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  62

1.  Introduction

   There exist today a collection of modem devices that control links of
   variable datarate and quality.  Examples of these types of links
   include line-of-sight (LOS) terrestrial radios, satellite terminals,
   and cable/DSL modems.  Fluctuations in speed and quality of these
   links can occur due to configuration (in the case of cable/DSL
   modems), or on a moment-to-moment basis, due to physical phenomena
   like multipath interference, obstructions, rain fade, etc.  It is
   also quite possible that link quality and datarate varies with
   respect to individual destinations on a link, and with the type of
   traffic being sent.  As an example, consider the case of an 802.11g
   access point, serving 2 associated laptop computers.  In this
   environment, the answer to the question "What is the datarate on the
   802.11g link?" is "It depends on which associated laptop we're
   talking about, and on what kind of traffic is being sent."  While the
   first laptop, being physically close to the access point, may have a
   datarate of 54Mbps for unicast traffic, the other laptop, being
   relatively far away, or obstructed by some object, can simultaneously
   have a datarate of only 32Mbps for unicast.  However, for multicast
   traffic sent from the access point, all traffic is sent at the base
   transmission rate (which is configurable, but depending on the model
   of the access point, is usually 24Mbps or less).

   In addition to utilizing variable datarate links, mobile networks are
   challenged by the notion that link connectivity will come and go over
   time, without an effect on a router's interface state (Up or Down).
   Effectively utilizing a relatively short-lived connection is
   problematic in IP routed networks, as routing protocols tend to rely
   on interface state and independent timers at OSI Layer 3 to maintain
   network convergence (e.g. (e.g., HELLO messages and/or recognition of DEAD
   routing adjacencies).  These dynamic connections can be better
   utilized with an event-driven paradigm, where acquisition of a new
   neighbor (or loss of an existing one) is signaled, as opposed to a
   paradigm driven by timers and/or interface state.

   Another complicating factor for mobile networks are the different
   methods of physically connecting the modem devices to the router.
   Modems can be deployed as an interface card in a router's chassis, or
   as a standalone device connected to the router via Ethernet or serial
   link.  In the case of Ethernet or serial attachment, with existing
   protocols and techniques, routing software cannot be aware of
   convergence events occurring on the radio link (e.g. (e.g., acquisition or
   loss of a potential routing neighbor), nor can the router be aware of
   the actual capacity of the link.  This lack of awareness, along with
   the variability in datarate, leads to a situation where finding the
   (current) best route through the network to a given destination is
   difficult to establish and properly maintain.  This is especially
   true of demand-based access schemes such as Demand Assigned Multiple
   Access (DAMA) implementations used on some satellite systems.  With a
   DAMA-based system, additional datarate may be available, but will not
   be used unless the network devices emit traffic at a rate higher than
   the currently established rate.  Increasing the traffic rate does not
   guarantee additional datarate will be allocated; rather, it may
   result in data loss and additional retransmissions on the link.

   Addressing the challenges listed above, the authors have developed
   the Data Link Exchange Protocol, or DLEP.  The DLEP protocol runs
   between a router and its attached modem devices, allowing the modem
   to communicate link characteristics as they change, and convergence
   events (acquisition and loss of potential routing destinations).  The
   following diagrams are used to illustrate the scope of DLEP packets.

      |-------Local Node-------|          |-------Remote Node------|
      |                        |          |                        |
      +--------+       +-------+          +-------+       +--------+
      | Router |=======| Modem |{~~~~~~~~}| Modem |=======| Router |
      |        |       | Device|          | Device|       |        |
      +--------+       +-------+          +-------+       +--------+
               |       |       | Link     |       |       |
               |-DLEP--|       | Protocol |       |-DLEP--|
               |       |       | (e.g.    |       |       |
               |       |       | 802.11)  |       |       |

                          Figure 1: DLEP Network

   In Figure 1, when the local modem detects the presence of a remote
   node, it (the local modem) sends a signal to its router via the DLEP
   protocol.  Upon receipt of the signal, the local router may take
   whatever action it deems appropriate, such as initiating discovery
   protocols, and/or issuing HELLO messages to converge the network.  On
   a continuing, as-needed basis, the modem devices utilize DLEP to
   report any characteristics of the link (datarate, latency, etc) that
   have changed.  DLEP is independent of the link type and topology
   supported by the modem.  Note that the DLEP protocol is specified to
   run only on the local link between router and modem.  Some over the
   air signaling may be necessary between the local and remote modem in
   order to provide some parameters in DLEP signals between the local
   modem and local router, but DLEP does not specify how such over the
   air signaling is carried out.  Over the air signaling is purely a
   matter for the modem implementer.

   Figure 2 shows how DLEP can support a configuration where routers are
   connected with different link types.  In this example, Modem A
   implements a point-to-point link, and Modem B is connected via a
   shared medium.  In both cases, the DLEP protocol is used to report
   the characteristics of the link (datarate, latency, etc.) to routers.
   The modem is also able to use the DLEP session to notify the router
   when the remote node is lost, shortening the time required to re-converge re-
   converge the network.

                 +--------+                     +--------+
            +----+ Modem A|                     | Modem A+---+
            |    | Device |  <===== // ======>  | Device |   |
            |    +--------+      P-2-P Link     +--------+   |
        +---+----+                                       +---+----+
        | Router |                                       | Router |
        |        |                                       |        |
        +---+----+                                       +---+----+
            |     +--------+                     +--------+  |
            +-----+ Modem B|                     | Modem B|  |
                  | Device |   o o o o o o o o   | Device +--+
                  +--------+    o  Shared   o    +--------+
                                 o Medium  o
                                  o       o
                                   o     o
                                    o   o
                                      o
                                 +--------+
                                 | Modem B|
                                 | Device |
                                 +---+----+
                                     |
                                     |
                                 +---+----+
                                 | Router |
                                 |        |
                                 +--------+

            Figure 2: DLEP Network with Multiple Modem Devices

   DLEP defines a set of signals used by modems and their attached
   routers.  The signals are used to communicate events that occur on
   the physical link(s) managed by the modem: for example, a remote node
   entering or leaving the network, or that the link has changed.
   Associated with these signals are a set of data items - information
   that describes the remote node (e.g., address information), and/or
   the characteristics of the link to the remote node.

   The protocol is defined as a collection of type-length-value (TLV)
   based formats, specifying the signals that are exchanged between a
   router and a modem, and the data items associated with the signal.
   This document specifies transport of DLEP signals and data items via
   the TCP transport, with a UDP-based discovery mechanism.  Other
   transports for the protocol are possible, but are outside the scope
   of this document.

   DLEP signals are further defined as mandatory or optional. Signals
   will additionally have mandatory and optional data items.
   Implementations MUST support all mandatory signals and their
   mandatory data items to be considered compliant. Implementations MAY
   also support some, or all, of the optional signals and data items.

   DLEP uses a session-oriented paradigm between the modem device and
   its associated router.  If multiple modem devices are attached to a
   router (as in Figure 2), a separate DLEP session MUST exist for each
   modem.  If a modem device supports multiple connections to a router
   (via multiple logical or physical interfaces), or supports
   connections to multiple routers, a separate DLEP session MUST exist
   for each connection.  This router/modem session provides a carrier
   for information exchange concerning "destinations" 'destinations' that are available
   via the modem device.  A "destination" 'destination' can be either physical (as in
   the case of a specific far-end router), or a logical destination (as
   in a Multicast group).  As such, all of the destination-level
   exchanges in DLEP can be envisioned as building an information base
   concerning the remote nodes, and the link characteristics to those
   nodes.

   Any DLEP signal that is NOT understood by a receiver MUST result in
   an error indication being sent to the originator, and also MUST
   result in termination of the session between the DLEP peers.  Any
   data item that is NOT understood by a receiver MUST be ignored.

   Multicast traffic destined for the variable-quality network (the
   network accessed via the DLEP modem) is handled in IP networks by
   deriving a Layer 2 MAC address based on the Layer 3 address.
   Leveraging on this scheme, Multicast traffic is supported in DLEP
   simply by treating the derived MAC address as any other "destination" 'destination'
   (albeit a logical one) in the network.  To support these logical
   destinations, one of the DLEP participants (typically, the router)
   informs the other as to the existence of the logical neighbor.  The
   modem, once it is aware of the existence of this logical neighbor,
   reports link characteristics just as it would for any other
   destination in the network.  The specific algorithms a modem would
   use to report metrics on multicast (or logical) destinations is
   outside the scope of this specification, and is left to specific
   implementations to decide.

1.1

1.1.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119].

2.  Assumptions

   Routers and modems that exist as part of the same node (e.g., that
   are locally connected) can utilize a discovery technique to locate
   each other, thus avoiding a-priori configuration.  The router is
   responsible for initialing initializing the discovery process, using the Peer
   Discovery signal. signal (Section 7.1).

   DLEP utilizes a session-oriented paradigm.  A router and modem form a
   session by completing the discovery process.  This router-modem
   session persists unless or until it either (1) times out, based on
   the timeout values supplied, or (2) is explicitly torn down by one of
   the participants.  Note that while use of timers in DLEP is OPTIONAL,
   it is strongly recommended that implementations choose to run with
   timers enabled.

   DLEP assumes that participating modems, and their physical links, act
   as a transparent IEEE 802.1D bridge. Specifically, the assumption is
   that the destination MAC address for delivering data traffic (frames destined
   for the far-end node, as opposed to is the DLEP control traffic itself)
   MAC specified in any frame emitted by the router should be Destination Up signal (Section 7.9).  No
   manipulation or or substitution is performed; the MAC address of a
   device
   supplied in Destination Up is used as the remote node. DLEP also assumes OSI Layer 2 Destination MAC
   address.  DLEP also assumes that MAC addresses are MUST be unique within
   the context of the a router-modem session.

   DLEP utilizes UDP multicast for single-hop discovery, and TCP for
   transport of the control signals.  Therefore, DLEP assumes that the
   modem and router have topologically consistent IP addresses assigned.
   It is recommended that DLEP implementations utilize IPv6 link-local
   addresses to reduce the administrative burden of address assignment.

   This document refers to a remote node as a "Destination". 'Destination'.
   Destinations can be identified by either the router or the modem, and
   represent a specific destination (e.g., an address) that exists on
   the link(s) managed by the modem.  A destination MUST contain a MAC
   address, it MAY optionally include a Layer 3 address (or addresses).
   Destinations MAY refer either to physical devices in
   Note that since a destination is a MAC address, the network, or
   to MAC could
   reference a logical destinations, destination, as in a derived multicast MAC address
   associated with
   address, as well as to a group. physical device.  As "destinations" destinations are
   discovered, DLEP routers and modems build an information base on
   destinations accessible via the modem.  Changes in link
   characteristics MAY are then be reported as being "modem-wide" 'modem-wide' (effecting
   ALL destinations accessed via the modem) modem, reported via the Peer Update
   signal, Section 7.5) or MAY be reported for a specific neighbor (destination) specific. (via the
   Destination Update signal, Section 7.13).

   The DLEP signals concerning destinations thus become the way for
   routers and modems to maintain, and notify each other about, an
   information base representing the physical and logical (e.g.,
   multicast) destinations accessible via the modem device.  The
   information base would contain addressing information (e.g., (i.e., MAC
   address, and OPTIONALLY, Layer 3 addresses), link characteristics
   (metrics), and OPTIONALLY, flow control information (credits).

   DLEP assumes that security on the session (e.g. (e.g., authentication of
   session partners, encryption of traffic, or both) is dealt with by
   the underlying transport mechanism (e.g., by using a transport such
   as TLS [TLS]). [RFC5246]).

   This document specifies an implementation of the DLEP signals and
   data items running over the TCP transport.  It is assumed that DLEP
   running over other transport mechanisms would be documented
   separately.

3. Mandatory Versus  Core Features and Optional Items

   As mentioned above, Extensions

   DLEP defines has a core set of signals and data items
   as mandatory. Support for those signals and data items that MUST exist in be processed
   without error by an implementation in order to guarantee
   interoperability and therefore make an the implementation DLEP
   compliant. However, a mandatory signal or data
   item is not necessarily required - as an example, consider  This document defines the data
   item entitled "DLEP Optional Signals Supported", defined in section
   10.22 core set of this document. The data item allows a DLEP implementation to
   list all optional behavior it supports, signals and is sent data
   items, listing them as a part of the
   Peer Initialization signal. Receiving implementations MUST 'mandatory'.  It should be capable
   of parsing and understanding the optional signals noted that are offered.
   However, if the sending implementation has chosen NOT to implement
   ANY optional functionality, this some
   core signals and data item would NOT items might not be included in
   the Peer Initialization. Although parsing and understanding used during the data
   item is a mandatory function lifetime of
   a single DLEP session, but a compliant DLEP, the data item
   itself MAY, or MAY NOT, appear in implementation MUST support
   them.

   While this document represents the flow. Absence best efforts of the mandatory
   data item would not be considered a protocol error, but as support
   for co-authors,
   and the core DLEP signals ONLY. Therefore, care should be taken working group, to
   differentiate the notion of a mandatory data item versus one be functionally complete, it is recognized
   that
   MUST appear in a given message.

4. Credits extensions to DLEP includes will in all likelihood be necessary as more
   link types are utilized.  To support future extension of DLEP, this
   document describes an OPTIONAL credit-windowing scheme analogous extension negotiation capability to be used
   during session initialization via the
   one Extensions Supported data item,
   documented in [RFC5578]. In Section 8.6 of this scheme, traffic between document.

   All extensions are considered OPTIONAL.  Only the
   router and modem is treated as two unidirectional windows. This
   document identifies these windows DLEP functionality
   listed as the "Modem Receive Window", or
   MRW, and the "Router Receive Window", or RRW.

   If the OPTIONAL credit-windowing scheme 'mandatory' is used, credits MUST be
   granted required by implementation in order to be
   DLEP compliant.

   This specification defines one extension, Credit processing, exposed
   via the receiver on a given window - Extensions Supported mechanism that is, on the "Modem
   Receive Window" (MRW), the modem is responsible for granting credits implementations MAY chose
   to the router, allowing it (the router) implement, or to send data omit.

3.1.  Negotiation of Optional Extensions

   Optional extensions supported by an implementation MUST be declared
   to potential DLEP peers using the modem.
   Likewise, the router is responsible for granting credits on the RRW,
   which allows the modem to send Extensions Supported data to item
   (Section 8.6) during the router.

   DLEP expresses all credit session initialization sequence.  Once both
   peers have exchanged initialization signals, an implementation MUST
   NOT emit any signal or data item associated with an optional
   extension that was not specified in number of octets. The total number
   of credits on a window, and the increment to add to a grant, received initialization
   signal from its peer.

3.2.  Protocol Extensions

   If/when protocol extensions are
   always expressed as a 64-bit unsigned quantity.

   If used, credits are managed on a neighbor-specific basis; that is,
   separate credit counts are maintained required, they should be standardized
   either as an update to this document, or as an additional stand-alone
   specification.  The requests for each neighbor requiring IANA-controlled registries in this
   document contain sufficient reserved space, both in terms of DLEP
   signals and DLEP data items, to accomodate future extensions to the
   service. Credits do not apply
   protocol and the data transferred.

3.3.  Experimental Signals and Data Items

   This document requests numbering space in both the DLEP signal and
   data item registries for experimental items.  The intent is to allow
   for experimentation with new signals and/or data items, while still
   retaining the documented DLEP session that exists behavior.  If a given experiment proves
   successful, it SHOULD be documented as an update to this document, or
   as a stand-alone specification.

   Use of the experimental signals or data items MUST be announced by
   inclusion of an Experimental Definition data item (Section 8.7) with
   a value agreed upon (a-priori) between
   routers the participating peers.  The
   exact mechanism for a-priori communication of the experimental
   definition formats is beyond the scope of this document.

   Multiple Experimental Definition data items MAY appear in the Peer
   Initialization/Peer Initialization ACK sequence.  However, use of
   multiple experiments in a single peer session could lead to
   interoperability issues or unexpected results (e.g., redefinition of
   experimental signals and/or data items), and modems.

5. is therefore
   discouraged.  It is left to implementations to determine the correct
   processing path (e.g., a decision on whether to terminate the peer
   session, or to establish a precedence of the conflicting definitions)
   if such conflicts arise.

4.  Metrics

   DLEP includes the ability for the router and modem to communicate
   metrics that reflect the characteristics (e.g. (e.g., datarate, latency) of
   the variable-quality link in use.  DLEP does NOT specify how a given
   metric value is to be calculated, rather, the protocol assumes that
   metrics have been calculated with a "best effort", 'best effort', incorporating all
   pertinent data that is available to the modem device.

   As mentioned in the introduction section of this document, metrics
   have to be used within a context - for example, metrics to a unicast
   address in the network.  DLEP allows for metrics to be sent within
   two contexts - metrics for a specific destination within the network
   (e.g., a specific router), and "modem-wide" 'modem-wide' (those that apply to all
   destinations accessed via the modem).  Metrics can be further
   subdivided into transmit and receive metrics.  Metrics supplied on
   DLEP Peer signals are, by definition, modem-wide; metrics supplied on
   Destination signals are, by definition, used for the specific
   neighbor only.

   DLEP modem implementations MUST announce all supported metric items,
   and provide default values for those metrics, in the Peer
   Initialization signal. signal (Section 7.3).  In order to introduce a new
   metric type, DLEP modem implementations MUST terminate the session
   with the router (via the Peer Terminate signal), signal, Section 7.7), and re-establish re-
   establish the session.

   It is left to implementations to choose sensible default values based
   on their specific characteristics.  Modems having static (non-
   changing) link metric characteristics MAY report metrics only once
   for a given neighbor (or once on a modem-wide basis, if all
   connections via the modem are of this static nature).

   The approach of allowing for different contexts for metric data
   increases both the flexibility and the complexity of using metric
   data.  This document details the mechanism whereby the data is
   transmitted, however, the specific algorithms (precedence, etc) for
   utilizing the dual-context metrics is out of scope and not addressed
   by this document.

6. Extensions to

4.1.  Mandatory Metrics

   As mentioned above, DLEP

   While this draft represents the best efforts of the co-authors, and
   the working group, to be functionally complete, it is recognized that
   extensions to DLEP will in modem implementations MUST announce all likelihood be necessary as more link
   types are utilized. There are three possible avenues for DLEP
   extensions: protocol extensions, vendor extensions, and experimental
   extensions.

6.1 Protocol Extensions

   If/when protocol extensions are required, they should be standardized
   either as an update to this document, or as
   supported metric items during session initialization.  However, an additional stand-alone
   specification.

6.2 Vendor Extensions

   Vendor extensions to DLEP are accommodated via the "DLEP Vendor
   Extension" TLV, documented in Section 10.22 of this document. If a
   perceived extension exceeds
   implementation MUST include the scope following list of what can be contained in the
   DLEP Vendor Extension TLV, the proposed extension should be addressed
   as either an update to this document, or as a stand-alone
   specification.

6.3 Experimental Extensions

   This document requests numbering space in both the Signal and metrics:

   o  Maximum Data
   Item registries for experimental items. The intent is to allow for
   experimentation with new signals and/or data items, while still
   retaining the documented DLEP behavior. If a given experiment proves
   successful, it SHOULD be documented as an update to this document, or
   as a stand-alone specification. Experimental DLEP signals SHOULD be
   treated as optional signals - e.g., they SHOULD be announced in the
   "DLEP Optional Signals TLV" in Peer Initialization and/or Peer
   Initialization ACK. Likewise, experimental data item TLVs SHOULD be
   announced in the "DLEP Optioinal Rate (Receive) (Section 8.13)

   o  Maximum Data Items" TLV (also in Peer
   Initialization/Peer Initialization ACK).

7. Rate (Transmit) (Section 8.14)

   o  Current Data Rate (Receive) (Section 8.15)

   o  Current Data Rate (Transmit) (Section 8.16)

   o  Latency (Section 8.17)

5.  Normal Session Flow

   Normal session flow for a DLEP router has two sub-cases, depending on
   whether the implementation supports the discovery process. Since
   modems  Modem
   implementations MUST support the discovery process, there is only one
   description necessary for modem implementations. The normal flow by
   DLEP partner type is:

7.1 Discovery case; router
   implementations MAY support discovery, or rely on a-priori
   configuration to define the address(es) of attached modems.

5.1.  DLEP Router session flow - Discovery case

   If the DLEP router implementation is utilizing the optional discovery
   mechanism, then the implementation will initialize a UDP socket,
   binding it to an arbitrary port.  This UDP socket is used to send the
   Peer Discovery signal (Section 7.1) to the DLEP link-local multicast
   address and port (TBD).  The implementation then waits on receipt of
   a Peer Offer
   signal, signal (Section 7.2), which MUST contain the unicast
   address and port for TCP-based communication with a DLEP modem.  The
   Peer Offer signal MAY contain multiple address/port combinations.  If
   more than one address/port combination is in the Peer Offer, the DLEP
   router implementation SHOULD consider the list to be in priority
   sequence, with the "most
   desired" 'most desired' address/port combination listed
   first.  However, router implementations MAY use their own heuristics
   to determine the best address/port combination.  At this point, the
   router implementation MAY either destroy the UDP socket, or continue
   to issue Peer Discovery signals to the link-local address/port
   combination.  In either case, the TCP session initialization occurs
   as in the configured case.

7.2

5.2.  DLEP Router session flow - Configured case

   When a DLEP router implementation has the address and port
   information for a TCP connection to a modem (obtained either via
   configuration or via the discovery process described above), the
   router will initialize and bind a TCP socket.  This socket is used to
   connect to the DLEP modem software.  After a successful TCP connect,
   the modem implementation MUST issue a Peer Initialization signal
   (Section 7.3) to the DLEP router.  The Peer Initialization signal
   MUST contain TLVs data items for ALL supported metrics from this modem (e.g. all mandatory metrics
   plus all optional metrics supported by the implementation), modem,
   along with the default values of those metrics.  After sending the
   Peer Initialization, the modem implementation MUST wait for receipt
   of a Peer Initialization ACK signal (Section 7.4) from the router.
   Receipt of the Peer Initialization ACK signal indicates that the
   router has received and processed the Peer Initialization, and the
   session MUST transition to the "in session" 'in session' state.  At this point,
   signals regarding destinations in the network, and/or Peer Update signals,
   signals (Section 7.5), can flow on the DLEP session between modem and
   router.  The "in session" 'in session' state is maintained until one of the
   following conditions occur:

   o  The session is explicitly terminated (using Peer Termination), or

   o  The session times out, based on supplied timeout values.

7.3

5.3.  DLEP Modem session flow

   DLEP modem implementations MUST support the discovery mechanism.
   Therefore, the normal flow is as follows:

   The implementation will initialize a UDP socket, binding that socket
   to the DLEP link-local multicast address (TBD) and the DLEP well-
   known port number (also TBD).  The implementation will then
   initialize a TCP socket, on a unicast address and port.  This socket
   is used to listen for incoming TCP connection requests.

   When the modem implementation receives a Peer Discovery signal
   (Section 7.1) on the UDP socket, it responds by issuing a Peer Offer
   signal (Section 7.2) to the sender of the Peer Discovery. Discovery signal.  The
   Peer Offer signal MUST contain the unicast address and port of the
   TCP listen socket, described above.  A DLEP modem implementation MAY
   respond with ALL address/port combinations that have an active TCP
   listen posted.  If multiple address/port combinations are listed, the
   receiver of the Peer Offer signal MAY connect on any available
   address/port pair.  Anything other than Peer Discovery signals
   received on the UDP socket MUST be silently dropped.

   When the DLEP modem implementation accepts a connection via TCP, it
   MUST send a Peer Initialization signal. signal (Section 7.3).  The Peer
   Initialization signal MUST contain metric TLVs data items for ALL mandatory metrics, and MUST contain
   metric TLVs for ANY optional metrics
   supported by the modem. metrics.  If a new an additional metric is to be introduced, the
   DLEP session between router and modem MUST be terminated and
   restarted, and the new metric described in a Peer Initialization
   signal.

7.4

5.4.  Common Session Flow

   In order to maintain the session between router and modem, periodic
   "Heartbeat"
   Heartbeat signals (Section 7.14) MAY be exchanged.  These signals are
   intended to keep the session alive, and to verify bidirectional
   connectivity between the two participants.  DLEP also provides an OPTIONAL a Peer
   Update signal, signal (Section 7.5), intended to communicate some change in
   status (e.g., a change of layer 3 address parameters, or a modem-wide
   link change).

   In addition to the local (Peer level) signals above, the participants
   will transmit DLEP signals concerning destinations in the network.
   These signals trigger creation/maintenance/deletion of destinations
   in the information base of the recipient.  For example, a modem will
   inform its attached router of the presence of a new destination via
   the "Destination Up" signal. Destination Up signal (Section 7.9).  Receipt of a Destination Up
   causes the router to allocate the necessary resources, creating an
   entry in the information base with the specifics (e.g., (i.e., MAC Address,
   Latency, Data Rate, etc) of the neighbor.  The loss of a destination
   is communicated via the "Destination Down" signal, Destination Down signal (Section 7.11), and
   changes in status to the destination (e.g. (e.g., varying link quality, or
   addressing changes) are communicated via the "Destination Update" signal. Destination Update
   signal (Section 7.13).  The information on a given neighbor will
   persist in the router's information base until (1) a "Destination Down" Destination Down
   signal is received, indicating that the modem has lost contact with
   the remote node, or (2) the router/modem session terminates,
   indicating that the router has lost contact with its own local modem.

   Again, metrics

   Metrics can be expressed within the context of a specific neighbor
   via the Destination Update signal, or on a modem-wide basis via the
   Peer Update signal.  In cases where metrics are provided on the
   router/modem session, the receiver MUST propagate the metrics to all
   destinations in its information base that are accessed via the
   originator.  A DLEP participant MAY send metrics both in a
   router/modem router/
   modem session context (via the Peer Update signal) and a specific
   neighbor context (via Destination Update) at any time.  The
   heuristics for applying received metrics is left to implementations.

   In addition to receiving metrics about the link, DLEP provides an
   OPTIONAL a
   signal allowing a router to request a different datarate, or latency,
   from the modem.  This signal is referred to as the Link
   Characteristics Signal, Request signal (Section 7.15), and gives the router
   the ability to deal with requisite increases (or decreases) of
   allocated datarate/latency in demand-based schemes in a more
   deterministic manner.

8. Mandatory Signals

6.  DLEP Message Processing

   Communication between DLEP peers consists of a bidirectional stream
   of signals, each signal consisting of a signal header and Data Items

   The an
   unordered list of data items.  Both signal headers and data items are
   encoded as TLV (Type-Length-Value) structures.  In this document, the
   data items following DLEP signals the signal header are considered core to described as being
   'contained in' the specification;
   implementations signal.

   All integer values in all TLV structures MUST support these signals, be in network byte-
   order.

   There is no restriction on the order of data items following a
   signal, and the associated multiplicity of duplicate data
   items, items is defined by
   the definition of the signal declared by the type in order to be considered compliant:

         Signal                        Data Items
         ======                        ==========
         Peer Discovery (Router Only)  None

         Peer Offer (Modem Only)       IPv4 Address
                                       IPv6 address
                                       DLEP Port

         Peer Initialization           Maximum Data Rate (Receive)
                                       Maximum Data Rate (Transmit)
                                       Current Data Rate (Receive)
                                       Current Data Rate (Transmit)
                                       Latency
                                       Relative Link Quality (Receive)
                                       Relative Link Quality (Transmit)
                                       DLEP Optional Signal Support
                                       DLEP Optional Data Item Support

         Peer Initialization ACK       Status the signal
   header.

   If an unrecognized, or unexpected signal is received, or a received
   signal contains unrecognized, invalid or disallowed duplicate data
   items, the receiving peer MUST terminate the session by issuing a
   Peer Termination signal (Section 7.7) with a Status

         Peer Termination ACK          Status

         Destination Up                MAC Address
                                       Maximum Data Rate (Receive)
                                       Maximum Data Rate (Transmit)
                                       Current Data Rate (Receive)
                                       Current Data Rate (Transmit)
                                       Latency
                                       Relative Link Quality (Receive)
                                       Relative Link Quality (Transmit)

         Destination Update            MAC Address
                                       Maximum Data Rate (Receive)
                                       Maximum Data Rate (Transmit)
                                       Current Data Rate (Receive)
                                       Current Data Rate (Transmit)
                                       Latency
                                       Relative Link Quality (Receive)
                                       Relative Link Quality (Transmit)

         Destination Down              MAC Address

   All other DLEP signals and data items are OPTIONAL. Implementations
   MAY choose to provide them. Implementations that do not support
   optional signals MUST report an error condition item
   (Section 8.2) containing the most relevant status code, and terminate then
   close the
   router/modem session upon receipt of any such signal received.
   OPTIONAL data items received that are not supported MUST be silently
   dropped.

9. Generic TCP connection:

6.1.  DLEP Signal Definition Header

   The Generic DLEP Signal consists of a sequence of TLVs. The first TLV
   represents the signal being communicated (e.g., a "Destination Up",
   or a "Peer Offer"). Subsequent TLVs contain the data items pertinent
   to the signal (e.g., Maximum Data Rate, or Latency, etc).

   The Generic DLEP Packet Definition header contains the following fields:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Signal TLV
     | Signal Type   | Length                        | DLEP data items...   | Data Items...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 3: DLEP Signal               - Header

   Signal Type:  One of the DLEP Signal TLV type Type values defined in this
      document.

      Length               -

   Length:  The length, expressed as a 16-bit
                             quantity, unsigned integer, of all
      of the DLEP data items associated with this signal.

      DLEP data items      -  This length
      does not include the length of the header itself

   Data Items:  One or more DLEP data items, encoded in TLVs, as defined
      in this document.

10.

6.2.  DLEP Generic Data Items

   As mentioned earlier, DLEP protocol signals are transported as a
   collection of TLVs. The first TLV present in a Item

   All DLEP signal MUST be
   one of the Signal TLVs, documented in section 10. The signals are
   followed by one or more data items, indicating the specific changes
   that need to be instantiated in the receiver's information base.

   Valid DLEP Data Items are:

          TLV      TLV
          Value    Description
          =========================================
          TBD      DLEP Port
          TBD      Peer Type
          TBD      IPv4 Address
          TBD      IPv6 Address
          TBD      Maximum Data Rate (Receive)  (MDRR)
          TBD      Maximum Data Rate (Transmit) (MDRT)
          TBD      Current Data Rate (Receive)  (CDRR)
          TBD      Current Data Rate (Transmit) (CDRT)
          TBD      Latency
          TBD      Receive Resources
          TBD      Transmit Resources
          TBD      Relative Link Quality (Receive)  (RLQR)
          TBD      Relative Link Quality (Transmit) (RLQT)
          TBD      Status
          TBD      Heartbeat Interval/Threshold
          TBD      Neighbor down ACK timer
          TBD      Link Characteristics ACK timer
          TBD      Credit Window Status
          TBD      Credit Grant
          TBD      Credit Request
          TBD      DLEP Optional Signals Supported
          TBD      DLEP Optional Data Items Supported
          TBD      DLEP Vendor Extension

   DLEP data item TLVs contain data items contain the following fields:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  TLV Type     | Data Item Type| Length        | Value...                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type    -

                     Figure 4: DLEP Generic Data Item

   Data Item Type:  An 8-bit unsigned integer field specifying the data
      item being sent.

   Length      -

   Length:  An 8-bit length of the value field of the data item

   Value       - item.

   Value:  A field of length <Length> which contains data specific to a
      particular data item.

10.1

7.  DLEP Version

      The Signals

   As mentioned above, all DLEP Version TLV is a mandatory TLV signals begin with the DLEP signal
   header structure.  Therefore, in the Peer Discovery,
   Peer Initialization, following descriptions of
   specific signals, this header structure is assumed, and Peer Initialization ACK signals. The Version
   TLV will not be
   replicated.

   Following is used to indicate the version set of the protocol running in the
   originator. A DLEP implementation MAY use this information to decide
   if the potential session partner is running at MANDATORY signals that must be recognized by
   a supported level.

   The DLEP Version TLV contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length=4 compliant implementation.  As mentioned before, not all
   signals may be used during a session, but an implementation MUST
   correctly process these signals when received.

   The mandatory DLEP signals are:

        +---------+-------------------------------+---------------+
        |         Major Version Signal  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Description                   |       Minor Version Section       |
        +---------+-------------------------------+---------------+
        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type      - TBD

   Length        - Length is 4

   Major Version - Major version of the modem or router protocol.

   Minor Version - Minor version of the modem or router protocol.

   Support of this draft is indicated by setting the Major Version to
   '0', and the Minor Version to '7' (e.g. Version 0.7).

10.2  DLEP Port

   The DLEP Port TLV is a mandatory TLV in the     | Peer Discovery                | Section 7.1   |
        | TBD     | Peer Offer signal. The
   DLEP Port TLV is used to indicate the TCP Port number on the DLEP
   server available for connections. The receiver MUST use this
   information to perform the TCP connect to the DLEP server.

   The DLEP Port TLV contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length=2                    |       TCP Port Number Section 7.2   |
        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type        - TBD

   Length          - Length is 2

   TCP Port Number - TCP Port number on the DLEP server.

10.3     | Peer Type

   The Initialization           | Section 7.3   |
        | TBD     | Peer Type TLV is an OPTIONAL TLV in both the Peer Discovery and Initialization ACK       | Section 7.4   |
        | TBD     | Peer Offer signals. The Update                   | Section 7.5   |
        | TBD     | Peer Type TLV is used by the router and modem
   to give additional information as to its type. The peer type is a
   string and is envisioned to be used for informational purposes (e.g.
   as output in a display command).

   The Update ACK               | Section 7.6   |
        | TBD     | Peer Type TLV contains the following fields:

   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |TLV Type =TBD  |Length= peer   |Peer Type String Termination              | Section 7.7   |               |type string len|
        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type         - TBD

   Length           - Length of peer type string.     | Peer Type String - Non-Null terminated string, using UTF-8 encoding.
                      For example, a satellite modem might set this
                      variable to 'Satellite terminal'.

10.4  MAC Address

   The MAC address TLV MUST appear in all destination-oriented signals
   (e.g. Termination ACK          | Section 7.8   |
        | TBD     | Destination Up, Up                | Section 7.9   |
        | TBD     | Destination Up ACK, ACK            | Section 7.10  |
        | TBD     | Destination Down, Down              | Section 7.11  |
        | TBD     | Destination Down ACK, ACK          | Section 7.12  |
        | TBD     | Destination Update, Update            | Section 7.13  |
        | TBD     | Heartbeat                     | Section 7.14  |
        | TBD     | Link Characteristics
   Request, and Request  | Section 7.15  |
        | TBD     | Link Characteristics ACK). The MAC Address TLV contains ACK      | Section 7.16  |
        +---------+-------------------------------+---------------+

7.1.  Peer Discovery Signal

   A Peer Discovery signal SHOULD be sent by a router to discover DLEP
   routers in the address of the destination on the remote node. network.  The MAC address Peer Offer signal (Section 7.2) is
   required to complete the discovery process.  Implementations MAY be either a physical or a virtual destination. Examples of a
   virtual destination would be
   implement their own retry heuristics in cases where it is determined
   the Peer Discovery signal has timed out.

   To construct a multicast MAC address, or Peer Discovery signal, the
   broadcast MAC (0xFFFFFFFFFFFF).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 6     |          MAC Address          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      MAC Address                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Signal Type    - TBD

   Length      - 6

   MAC Address - MAC Address of value in the destination (either physical or
                 virtual).

10.5  IPv4 Address

   The IPv4 Address TLV
   signal header is an optional TLV. If supported, it MAY appear set to DLEP_PEER_DISCOVERY (value TBD).

   The Peer Discovery signal MUST contain one of each of the following
   data items:

   o  DLEP Version (Section 8.1)

   o  Heartbeat Interval (Section 8.5)

7.2.  Peer Offer Signal

   A Peer Offer signal MUST be sent by a DLEP modem in Destination Up, Destination Update, response to a
   Peer Initialization, Discovery signal (Section 7.1).  Upon receipt, and processing,
   of a Peer
   Update signals. When included Offer signal, the router responds by issuing a TCP connect
   to the address/port combination specified in Destination signals, the IPv4
   Address TLV contains received Peer Offer.

   The Peer Offer signal MUST be sent to the IPv4 unicast address of the destination, as well as
   a subnet mask value. In the
   originator of Peer Update signal, it contains Discovery.

   To construct a Peer Offer signal, the IPv4
   address of Signal Type value in the originator signal
   header is set to DLEP_PEER_OFFER (value TBD).

   The Peer Offer signal MUST contain one of each of the signal. In either case, the TLV also
   contains an indication following data
   items:

   o  DLEP Version (Section 8.1)

   o  Heartbeat Interval (Section 8.5)

   The Peer Offer signal MAY contain one of whether this is a new or existing address,
   or is a deletion each of a previously known address.

   The IPv4 Address TLV contains the following fields:

   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |TLV Type =TBD  |Length = 5     |   Add/Drop    | IPv4 Address  |
  |               |               |   Indicator   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |            IPv4 Address                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV data
   items:

   o  Peer Type     - TBD

   Length       - 6

   Add/Drop     - Value indicating whether this is a new or existing
                  address (0x01), (Section 8.4)

   o  DLEP Port (Section 8.3)

   The Peer Offer signal MAY contain one or a withdrawal more of an address (0x02).

   IPv4 Address - The IPv4 address any of the destination or peer.

   Subnet Mask  - A subnet mask (0-32) to be applied to the following
   data items, with different values:

   o  IPv4
                  address.

10.6  IPv6 Address

   The (Section 8.9), with Add/Drop indicator = 1

   o  IPv6 Address TLV is an optional TLV. (Section 8.10), with Add/Drop indicator = 1

   If supported, it MAY be used
   in the Destination Up, Destination Update, Peer Initialization, and Peer Update Signals. When included in Destination signals, this Offer signal includes a DLEP Port data
   item contains the IPv6 address of the destination. In item, the Peer
   Discovery and Peer Update, it contains the IPv6 address of port
   number specified MUST be used to establish the
   originating peer. In either case, TCP session.  If the data item also contains an
   indication of whether this is a new or existing address, or
   DLEP Port number is a
   deletion of a previously omitted, the receiver MUST use the DLEP well-
   known address, as well as a subnet mask. port number (Section 11.7) to establish the TCP connection.

   The IPv6 IP Address TLV contains data items indicate the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 17    |   Add/Drop    | IPv6 Address  |
   |               |               |   Indicator   |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                IPv6 Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type     - TBD

   Length       - 17

   Add/Drop     - Value indicating whether this is a new or existing
                  address (0x01), or a withdrawal of an unicast address (0x02).

   IPv6 Address - IPv6 Address the receiver
   of Peer Offer MUST use when connecting the destination or peer.

10.7  Maximum Data Rate (Receive)

   The Maximum Data Rate Receive (MDRR) TLV is a mandatory data item,
   used DLEP TCP session.  If
   multiple IP Address items are present in Destination Up, Destination Update, Peer Initialization, the Peer
   Update, and Link Characteristics ACK Signals Offer signal,
   implementations MAY use their own heuristics to indicate select the maximum
   theoretical address to
   connect to.  If no IP Address data rate, items are included in bits per second, that can be achieved while
   receiving data on the link. When metrics are reported via Peer
   Offer signal, the signals
   listed above, receiver MUST use the maximum data rate receive origin address of the signal
   as the IP address to establish the TCP connection.

7.3.  Peer Initialization Signal

   A Peer Initialization signal MUST be reported.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 8     |          MDRR (bps)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        MDRR (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           MDRR (bps)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type          -  TBD
   Length            -  8

   Maximum Data Rate Receive -  A 64-bit unsigned number, representing sent by a router as the maximum theoretical data rate, in bits per
                        second (bps), that can be achieved while
                        receiving on first
   signal of the link.

10.8  Maximum Data Rate (Transmit)

   The Maximum Data Rate Transmit (MDRT) TLV DLEP TCP session.  It is sent by the router after a mandatory data item,
   used in Destination Up, Destination Update, Peer Initialization, Peer
   Update, and Link Characteristics ACK Signals TCP
   connect to indicate the maximum
   theoretical data rate, in bits per second, an address/port combination that can be achieved while
   transmitting data on the link. When metrics are reported was obtained either via
   receipt of a Peer Offer, or from a-priori configuration.

   If any optional extensions are supported by the
   signals listed above, the maximum data rate transmit implementation, they
   MUST be
   reported.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 8     |          MDRT (bps)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        MDRT (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           MDRT (bps)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type          -  TBD

   Length            -  8

   Maximum Data Rate Transmit -  A 64-bit unsigned number, representing
                        the maximum theoretical data rate, enumerated in bits per
                        second (bps), that can be achieved while
                        transmitting on the link.

10.9  Current Data Rate (Receive)

   The Current Data Rate Receive (CDRR) TLV is a mandatory Extensions Supported data item,
   used item.  If an
   Extensions Supported data item does NOT exist in Destination Up, Destination Update, Peer Initialization, a Peer
   Update, Link Characteristics Request, and Link Characteristics ACK
   signals to indicate
   Initialization signal, the rate at which receiver of the link signal MUST conclude that
   there is currently operating NO support for receiving traffic. In the case of the Link Characteristics
   Request, CDRR represents extensions in the desired receive sender.

   If any experimental signals or data rate for items are used by the link.
   When metrics
   implementation, they MUST be enumerated in one or more Experimental
   Definition data items.  If there are reported via no Experimental Definition data
   items in a Peer Initialization signal, the signals above (e.g. Destination
   Update), receiver of the current data rate receive signal
   MUST be reported. conclude that NO experimental definitions are in use by the
   sender.

   To construct a Peer Initialization signal, the Signal Type value in
   the signal header is set to DLEP_PEER_INITIALIZATION (value TBD).

   The Current Data Rate Receive TLV contains Peer Initialization signal MUST contain one of each of the
   following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |TLV Flags=0x10 |Length = 8     |CDRR (bps)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        CDRR (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        CDRR (bps)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV data items:

   o  DLEP Version (Section 8.1)

   o  Heartbeat Interval (Section 8.5)

   The Peer Initialization signal MAY contain one of each of the
   following data items:

   o  Peer Type          -  TBD

   Length            -  8

   Current Data Rate Receive -  A 64-bit unsigned number, representing (Section 8.4)

   o  Extensions Supported (Section 8.6)

   The Peer Initialization signal MAY contain one or more of any of the current
   following data rate, in bits per second, that
                        is currently items, with different values:

   o  Experimental Definition (Section 8.7)

7.4.  Peer Initialization ACK Signal

   A Peer Initialization ACK signal MUST be achieved while receiving traffic
                        on the link. When used sent in response to a
   received Peer Initialization signal (Section 7.3).  The Peer
   Initialization ACK signal completes the Link
                        Characteristics Request, CDRR represents TCP-level DLEP session
   establishment; the
                        desired receive rate, in bits per second, on sender of the
                        link. If there signal should transition to an 'in-
   session' state when the signal is no distinction between current sent, and maximum receive data rates, current data
                        rate receive SHOULD be set equal the receiver should
   transition to the maximum
                        data rate receive.

10.10  Current Data Rate (Transmit)

   The Current Data Rate Receive (CDRT) TLV is 'in-session' state upon receipt (and successful
   parsing) of a mandatory Peer Initialization ACK signal.

   All supported metric data item,
   used items MUST be included in Destination Up, Destination Update, Peer Initialization, the Peer
   Update, Link Characteristics Request, and Link Characteristics
   Initialization ACK
   signals signal, with default values to indicate the rate at which the link is currently operating
   for transmitting traffic. In be used on a
   'modem-wide' basis.  This can be viewed as the case modem 'declaring' all
   supported metrics at DLEP session initialization.  Receipt of any
   DLEP signal containing a metric data item NOT included in the Link Characteristics
   Request, CDRT represents Peer
   Initialization ACK signal MUST be treated as an error, resulting in
   the desired transmit data rate for termination of the link.
   When metrics DLEP session between router and modem.

   If any optional extensions are reported via the signals above (e.g. Destination
   Update), supported by the current data rate transmit modem, they MUST be reported.

   The Current Data Rate Transmit TLV contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |TLV Flags=0x10 |Length = 8     |CDRT (bps)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        CDRT (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        CDRT (bps)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type          -  TBD

   Length            -  8

   Current Data Rate Transmit -  A 64-bit unsigned number, representing
   enumerated in the current Extensions Supported data rate, item.  If an Extensions
   Supported data item does NOT exist in bits per second, a Peer Initialization ACK
   signal, the receiver of the signal MUST conclude that there is currently be achieved while transmitting
                        traffic on the link. When used NO
   support for extensions in the Link
                        Characteristics Request, CDRT represents sender.

   If any experimental signals or data items are used by the
                        desired transmit rate,
   implementation, they MUST be enumerated in bits per second, on
                        the link. one or more Experimental
   Definition data items.  If there is are no distinction between
                        current and maximum transmit data rates, current Experimental Definition data rate transmit
   items in a Peer Initialization ACK signal, the receiver of the signal
   MUST be conclude that NO experimental definitions are in use by the
   sender.

   After the Peer Initialization/Peer Initialization ACK signals have
   been successfully exchanged, implementations MUST only utilize
   extensions and experimental definitions that are supported by BOTH
   peers.

   To construct a Peer Initialization ACK signal, the Signal Type value
   in the signal header is set equal to DLEP_PEER_INIT_ACK (value TBD).

   The Peer Initialization ACK signal MUST contain one of each of the
                        maximum
   following data rate transmit.

10.11 items:

   o  DLEP Version (Section 8.1)

   o  Heartbeat Interval (Section 8.5)

   o  Maximum Data Rate (Receive) (Section 8.13)
   o  Maximum Data Rate (Transmit) (Section 8.14)

   o  Current Data Rate (Receive) (Section 8.15)

   o  Current Data Rate (Transmit) (Section 8.16)

   o  Latency (Section 8.17)

   The Latency TLV is a mandatory data item. It is used in Peer
   Initialization, Destination Up, Destination Update, Peer
   Initialization, Initialization ACK signal MAY contain one of each of the
   following data items:

   o  Status (Section 8.2)

   o  Peer Update, Type (Section 8.4)

   o  Resources (Receive) (Section 8.18)

   o  Resources (Transmit) (Section 8.19)

   o  Relative Link Characteristics Request, and Quality (Receive) (Section 8.20)

   o  Relative Link
   Characteristics Quality (Transmit) (Section 8.21)

   o  Extensions Supported (Section 8.6)

   The Peer Initialization ACK signals to indicate the amount of latency on the
   link, signal MAY contain one or in the case more of any of
   the Link Characteristics Request, following data items, with different values:

   o  Experimental Definition (Section 8.7)

7.5.  Peer Update Signal

   A Peer Update signal MAY be sent by a DLEP peer to indicate
   the maximum latency required local
   Layer 3 address changes, or for metric changes on a modem-wide basis.
   For example, addition of an IPv4 address to the link.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 4     | Latency in microseconds       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Latency (Cont.) microsecs    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type    -  TBD

   Length      -  4
   Latency     -  A 32-bit unsigned value, representing the transmission
                  delay router MAY prompt a
   Peer Update signal to its attached DLEP modems.  Also, a modem that
   changes its Maximum Data Rate for all destinations MAY reflect that
   change via a packet encounters as it is transmitted
                  over Peer Update signal to its attached router(s).

   Concerning Layer 3 addresses, if the link. In Destination Up, Destination Update,
                  and Link Characteristics ACK, this value modem is reported
                  as delay, in microseconds. The calculation capable of latency
                  is implementation dependent. For example,
   understanding and forwarding this information (via proprietary
   mechanisms), the latency
                  may be address update would prompt any remote DLEP modems
   (DLEP-enabled modems in a running average calculated from the internal
                  queuing. If remote node) to issue a device cannot calculate latency, this
                  TLV SHOUD NOT be issued. In Destination Update
   signal (Section 7.13) to their local routers with the Link Characteristics
                  Request Signal, this value represents new (or
   deleted) addresses.  Modems that do not track Layer 3 addresses
   SHOULD silently parse and ignore the maximum
                  delay, in microseconds, expected on Peer Update signal.  Modems that
   track Layer 3 addresses MUST acknowledge the link.

10.12  Resources (Receive)

   The Receive Resources TLV is an optional data item. If supported, it
   is used in Destination Up, Destination Update, Peer Initialization, Update with a Peer Update, and Link Characteristics
   Update ACK signals to indicate signal (Section 7.6).  Routers receiving a
   percentage (0-100) amount of resources (e.g. battery power),
   committed Peer Update
   with metric changes MUST apply the new metric to receiving data, remaining on all destinations
   (remote nodes) accessible via the originating peer. modem.  Supporting implementations
   are free to employ heuristics to retransmit Peer Update signals.  The Resources TLV contains the following fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 1     | Rcv Resources|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type    -  TBD

   Length      -  1

   Receive Resources   -  A percentage, 0-100, representing the amount
   sending of remaining resources, such as battery power,
                  allocated to receiving data. If a device cannot
                  calculate receive resources, this TLV Peer Update signals for Layer 3 address changes SHOULD
   cease when a either participant (router or modem) determines that the
   other implementation does NOT be
                  issued.

10.13  Resources (Transmit)

   The Transmit Resources TLV is an optional data item. support Layer 3 address tracking.

   If supported, it
   is used in Destination Up, Destination Update, Peer Initialization, metrics are supplied with the Peer Update, Update signal (e.g., Maximum
   Data Rate), these metrics are considered to be modem-wide, and Link Characteristics ACK signals
   therefore MUST be applied to indicate all destinations in the information base
   associated with the router/modem session.

   To construct a
   percentage (0-100) amount of resources (e.g. battery power),
   committed to transmitting data, remaining on Peer Update signal, the originating peer. Signal Type value in the
   signal header is set to DLEP_PEER_UPDATE (value TBD).

   The Resources TLV contains Peer Update signal MAY contain one of each of the following fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 1     | Xmt Resources|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type    -  TBD

   Length      -  1

   Transmit data
   items:

   o  Maximum Data Rate (Receive) (Section 8.13)

   o  Maximum Data Rate (Transmit) (Section 8.14)

   o  Current Data Rate (Receive) (Section 8.15)

   o  Current Data Rate (Transmit) (Section 8.16)

   o  Latency (Section 8.17)

   o  Resources   -  A percentage, 0-100, representing the amount
                  of remaining resources, such as battery power,
                  allocated to transmitting data. If the transmit
                  resources cannot be calculated, then the TLV SHOULD
                  NOT be issued.

10.14 (Receive) (Section 8.18)

   o  Resources (Transmit) (Section 8.19)

   o  Relative Link Quality (Receive)

   The (Section 8.20)

   o  Relative Link Quality Receive (RLQR) TLV is an optional data
   item. If supported, it is used in (Transmit) (Section 8.21)

   The Peer Initialization, Destination
   Up, Destination Update, Update signal MAY contain one or more of the following data
   items, with different values:

   o  IPv4 Address (Section 8.9)

   o  IPv6 Address (Section 8.10)

7.6.  Peer Initialization, Update ACK Signal

   A Peer Update, and Link
   Characteristics Update ACK signals signal MUST be sent by implementations supporting
   Layer 3 address tracking and/or modem-wide metrics to indicate
   whether a Peer Update signal (Section 7.5) was successfully
   processed.  If the quality Peer Update ACK is issued, it MUST contain a
   Status data item, indicating the success or failure of processing the link for
   receiving data as calculated by
   received Peer Update.

   To construct a Peer Update ACK signal, the originating peer. Signal Type value in the
   signal header is set to DLEP_PEER_UPDATE_ACK (value TBD).

   The Relative Link Quality (Receive) TLV contains Peer Update ACK signal MAY contain one of each of the following
   fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 1     |RCV Rel. Link  |
   |               |               |Quality (RLQR) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type              -  TBD

   Length                -  1

   Relative Link Quality (Receive) -  A non-dimensional number, 1-100,
                          representing relative link quality.
   data items:

   o  Status (Section 8.2)

   A value receiver of
                          100 represents a link of the highest quality.
                          If Peer Update ACK signal without a device cannot calculate the RLQR, this
                          TLV SHOULD NOT be issued.

10.15  Relative Link Quality (Transmit)

   The Transmit Link Quality Receive (RLQT) TLV is an optional Status data
   item. It is used in item
   MUST behave as if a Status data item with code 'Success' had been
   received.

7.7.  Peer Initialization, Destination Up, Destination
   Update, Termination Signal

   A Peer Initialization, Termination signal MUST be sent by a DLEP participant when the
   router/modem session needs to be terminated.  Implementations
   receiving a Peer Update, and Link Characteristics Termination signal MUST send a Peer Termination ACK signals
   signal (Section 7.8) to indicate the quality of the link for transmitting data
   as calculated by confirm the originating peer. termination process.  The Relative Link Quality (Transmit) TLV contains the following
   fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 1     |XMT Rel. Link  |
   |               |               |Quality (RLQR) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type              -  TBD

   Length                -  1

   Relative Link Quality (Transmit) -  A non-dimensional number, 1-100,
                          representing relative link quality. A value sender
   of
                          100 represents a link Peer Termination signal is free to define its heuristics in
   event of the highest quality.
                          If a device cannot calculate the RLQT, this
                          TLV SHOULD NOT be issued.

10.16  Status timeout.  The Status TLV is sent as part receiver of an acknowledgement signal, from
   either the modem or a Peer Termination signal MUST
   release all resources allocated for the router, router/modem session, and
   MUST eliminate all destinations in the information base accessible
   via the router/modem pair represented by the session.  Router and
   modem state machines are returned to indicate the success or failure of 'discovery' state.  No
   Destination Down signals (Section 7.11) are sent.

   To construct a given request.

   The Status TLV contains Peer Termination signal, the following fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 1     |     Code      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Signal Type         - TBD

   Length           - 1 value in the
   signal header is set to DLEP_PEER_TERMINATION (value TBD).

   The Peer Termination Code - 0 = Success, Non-zero = Failure. Specific values signal MAY contain one of each of a non-zero termination code depend on the
                          operation requested (e.g. Destination Up,
                          Destination Down, etc).

10.17  Heartbeat Interval

   The Heartbeat Interval TLV is following
   data items:

   o  Status (Section 8.2)

   A receiver of a mandatory TLV. It Peer Termination signal without a Status data item
   MUST behave as if a Status data item with status code 'Success' had
   been received.

7.8.  Peer Termination ACK Signal

   A Peer Termination ACK signal MUST be sent during
   Peer Initialization by a DLEP peer in response
   to indicate a received Peer Termination signal (Section 7.7).  Receipt of a
   Peer Termination ACK signal completes the desired Heartbeat timeout window.
   The receiver MUST either accept teardown of the timeout interval supplied by router/
   modem session.

   To construct a Peer Termination ACK signal, the
   sender, or reject Signal Type value in
   the signal header is set to DLEP_PEER_TERMINATION_ACK (value TBD).

   The Peer Initialization, and close the socket.
   Implementations Termination ACK signal MAY contain one of each of the
   following data items:

   o  Status (Section 8.2)

   A receiver of a Peer Termination ACK signal without a Status data
   item MUST implement heuristics such that behave as if a Status data item with status code 'Success'
   had been received.

7.9.  Destination Up Signal

   A DLEP signals
   sent/received reset participant MUST send a Destination Up signal to report that a
   new destination has been detected.  A Destination Up ACK signal
   (Section 7.10) is required to confirm a received Destination Up.  A
   Destination Up signal can be sent either by the timer interval. modem, to indicate
   that a new remote node has been detected, or by the router, to
   indicate the presence of a new logical destination (e.g., a Multicast
   group) exists in the network.

   The Interval sender of the Destination Up signal is used free to specify define its retry
   heuristics in event of a period (in seconds) for Heartbeat
   Signals (See Section 11.15). By specifying an Interval value timeout.  When a Destination Up signal is
   received and successfully processed, the receiver should add
   knowledge of 0,
   implementations MAY indicates the desire new destination to disable Heartbeat signals
   entirely (e.g., its information base, indicating
   that the Interval destination is accessible via the modem/router pair.

   To construct a Destination Up signal, the Signal Type value in the
   signal header is set to an infinite value), however,
   it is strongly recommended that implementations use non 0 timer
   values.

   A DLEP session will be considered inactive, and DLEP_DESTINATION_UP (value TBD).

   The Destination Up signal MUST be torn down, by
   an implementation detecting that two (2) Heartbeat intervals have
   transpired without receipt contain one of any DLEP signals. each of the following
   data items:

   o  MAC Address (Section 8.8)

   The Heartbeat Interval TLV contains Destination Up signal MAY contain one of each of the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 2     |           Interval            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type         - TBD

   Length           - 2

   Interval         - 0 = Do NOT use heartbeats on this peer-to-peer
                      session. Non-zero = Interval, in seconds, for
                      heartbeat signals.

10.18
   data items:

   o  Maximum Data Rate (Receive) (Section 8.13)

   o  Maximum Data Rate (Transmit) (Section 8.14)

   o  Current Data Rate (Receive) (Section 8.15)

   o  Current Data Rate (Transmit) (Section 8.16)

   o  Latency (Section 8.17)
   o  Resources (Receive) (Section 8.18)

   o  Resources (Transmit) (Section 8.19)

   o  Relative Link Characteristics ACK Timer

   The Quality (Receive) (Section 8.20)

   o  Relative Link Characteristics ACK Timer TLV is an optional TLV. Quality (Transmit) (Section 8.21)

   The Destination Up signal MAY contain one or more of the following
   data items, with different values:

   o  IPv4 Address (Section 8.9)

   o  IPv6 Address (Section 8.10)

   o  IPv4 Attached Subnet (Section 8.11)

   o  IPv6 Attached Subnet (Section 8.12)

   If
   supported, the sender has IPv4 and/or IPv6 address information for a
   destination it MAY be sent during Peer Initialization to indicate SHOULD include the
   desired number of seconds relevant data items in the
   Destination Up signal, reducing the need for the receiver to wait probe
   for any address.

7.10.  Destination Up ACK Signal

   A DLEP participant MUST send a response Destination Up ACK signal to indicate
   whether a Link
   Characteristics Request. If this TLV is omitted, implementations
   supporting Destination Up signal (Section 7.9) was successfully
   processed.

   To construct a Destination Up ACK signal, the Link Characteristics Request SHOULD choose a default
   value. Signal Type value in
   the signal header is set to DLEP_DESTINATION_UP_ACK (value TBD).

   The Link Characteristics Destination Up ACK Timer TLV contains signal MUST contain one of each of the
   following fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 1     | Interval      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type     - TBD

   Length       - 1

   Interval     - 0 = Do NOT use timeouts for Link Characteristics
                  requests on this router/modem session. Non-zero =
                  Interval, in seconds, to wait before considering data items:

   o  MAC Address (Section 8.8)

   The Destination Up ACK signal MAY contain one of each of the
   following data items:

   o  Status (Section 8.2)

   A receiver of a Destination Up ACK signal without a
                  Link Characteristics Request has been lost.

10.19  Credit Window Status

   The Credit Window data item
   MUST behave as if a Status TLV is an optional TLV. If credits are
   supported by the data item with status code 'Success' had
   been received.

7.11.  Destination Down Signal

   A DLEP participants (both the router and the modem),
   the Credit Window Status TLV peer MUST send a Destination Down signal to report when a
   destination (a remote node or a multicast group) is no longer
   reachable.  A Destination Down ACK signal (Section 7.12) MUST be sent
   by the participant
   receiving a Credit Grant Request for recipient of a given destination. Destination Down signal to confirm that the
   relevant data has been removed from the information base.  The Credit Window Status TLV contains sender
   of the following fields:

    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 Destination Down signal is free to define its retry heuristics
   in event of a timeout.

   To construct a Destination Down signal, the Signal Type value in the
   signal header is set to DLEP_DESTINATION_DOWN (value TBD).

   The Destination Down signal MUST contain one of each of the following
   data items:

   o  MAC Address (Section 8.8)

7.12.  Destination Down ACK Signal

   A DLEP participant MUST send a Destination Down ACK signal to
   indicate whether a received Destination Down signal (Section 7.11)
   was successfully processed.  If successfully processed, the sender of
   the ACK MUST have removed all entries in the information base that
   pertain to the referenced destination.

   To construct a Destination Down ACK signal, the Signal Type value in
   the signal header is set to DLEP_DESTINATION_DOWN_ACK (value TBD).

   The Destination Down ACK signal MUST contain one of each of the
   following data items:

   o  MAC Address (Section 8.8)

   The Destination Down ACK signal MAY contain one of each of the
   following data items:

   o  Status (Section 8.2)

   A receiver of a Destination Down ACK signal without a Status data
   item MUST behave as if a Status data item with status code 'Success'
   had been received.

7.13.  Destination Update Signal

   A DLEP participant SHOULD send the Destination Update signal when it
   detects some change in the information base for a given destination
   (remote node or multicast group).  Some examples of changes that
   would prompt a Destination Update signal are:

   o  Change in link metrics (e.g., Data Rates)

   o  Layer 3 4 5 6 7 8 9 addressing change (for implementations that support it)

   To construct a Destination Update signal, the Signal Type value in
   the signal header is set to DLEP_DESTINATION_UPDATE (value TBD).

   The Destination Update signal MUST contain one of each of the
   following data items:

   o  MAC Address (Section 8.8)

   The Destination Update signal MAY contain one of each of the
   following data items:

   o  Maximum Data Rate (Receive) (Section 8.13)

   o  Maximum Data Rate (Transmit) (Section 8.14)

   o  Current Data Rate (Receive) (Section 8.15)

   o  Current Data Rate (Transmit) (Section 8.16)

   o  Latency (Section 8.17)

   o  Resources (Receive) (Section 8.18)

   o  Resources (Transmit) (Section 8.19)

   o  Relative Link Quality (Receive) (Section 8.20)

   o  Relative Link Quality (Transmit) (Section 8.21)

   The Destination Update signal MAY contain one or more of the
   following data items, with different values:

   o  IPv4 Address (Section 8.9)

   o  IPv6 Address (Section 8.10)

   o  IPv4 Attached Subnet (Section 8.11)

   o  IPv6 Attached Subnet (Section 8.12)

7.14.  Heartbeat Signal

   A Heartbeat signal SHOULD be sent by a DLEP participant every N
   seconds, where N is defined in the Heartbeat Interval field of the
   Peer Initialization signal (Section 7.3) or Peer Initialization ACK
   signal (Section 7.4).  Note that implementations setting the
   Heartbeat Interval to 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV effectively set the interval to an infinite
   value, therefore, in those cases, this signal SHOULD NOT be sent.

   The signal is used by participants to detect when a DLEP session
   partner (either the modem or the router) is no longer communicating.
   Participants SHOULD allow two (2) heartbeat intervals to expire with
   no traffic on the router/modem session before initiating DLEP session
   termination procedures.

   To construct a Heartbeat signal, the Signal Type value in the signal
   header is set to DLEP_PEER_HEARTBEAT (value TBD).

   There are no valid data items for the Heartbeat signal.

7.15.  Link Characteristics Request Signal

   The Link Characteristics Request signal MAY be sent by the router to
   request that the modem initiate changes for specific characteristics
   of the link.  The request can reference either a real (e.g., a remote
   node), or a logical (e.g., a multicast group) destination within the
   network.

   The Link Characteristics Request signal contains either a Current
   Data Rate (CDRR or CDRT) data item to request a different datarate
   than what is currently allocated, a Latency data item to request that
   traffic delay on the link not exceed the specified value, or both.  A
   Link Characteristics ACK signal (Section 7.16) is required to
   complete the request.  Issuing a Link Characteristics Request with
   ONLY the MAC Address data item is a mechanism a peer MAY use to
   request metrics (via the Link Characteristics ACK) from its partner.

   The sender of a Link Characteristics Request signal MAY attach a
   timer to the request using the Link Characteristics ACK Timer data
   item.  If a Link Characteristics ACK signal is received after the
   timer expires, the sender MUST assume that the request failed.
   Implementations are free to define their retry heuristics in event of
   a timeout.

   To construct a Link Characteristics Request signal, the Signal Type
   value in the signal header is set to DLEP_LINK_CHAR_REQ (value TBD).

   The Link Characteristics Request signal MUST contain one of each of
   the following data items:

   o  MAC Address (Section 8.8)

   The Link Characteristics Request signal MAY contain one of each of
   the following data items:

   o  Link Characteristics ACK Timer (Section 8.22)

   o  Current Data Rate (Receive) (Section 8.15)

   o  Current Data Rate (Transmit) (Section 8.16)

   o  Latency (Section 8.17)

7.16.  Link Characteristics ACK Signal

   A DLEP participant MUST send a Link Characteristics ACK signal to
   indicate whether a received Link Characteristics Request signal
   (Section 7.15) was successfully processed.  The Link Characteristics
   ACK signal SHOULD contain a complete set of metric data items.  It
   MUST contain the same metric types as the request.  The values in the
   metric data items in the Link Characteristics ACK signal MUST reflect
   the link characteristics after the request has been processed.

   If an implementation is not able to alter the characteristics of the
   link in the manner requested, then a Status data item with status
   code 'Request Denied' MUST be added to the signal.

   To construct a Link Characteristics Request ACK signal, the Signal
   Type value in the signal header is set to DLEP_LINK_CHAR_ACK (value
   TBD).

   The Link Characteristics ACK signal MUST contain one of each of the
   following data items:

   o  MAC Address (Section 8.8)

   The Link Characteristics ACK signal MAY contain one of each of the
   following data items:

   o  Current Data Rate (Receive) (Section 8.15)

   o  Current Data Rate (Transmit) (Section 8.16)

   o  Latency (Section 8.17)
   o  Resources (Receive) (Section 8.18)

   o  Resources (Transmit) (Section 8.19)

   o  Relative Link Quality (Receive) (Section 8.20)

   o  Relative Link Quality (Transmit) (Section 8.21)

   o  Status (Section 8.2)

   A receiver of a Link Characteristics ACK signal without a Status data
   item MUST behave as if a Status data item with status code 'Success'
   had been received.

8.  DLEP Data Items

   Following is the list of MANDATORY data items that must be recognized
   by a DLEP compliant implementation.  As mentioned before, not all
   data items need be used during a session, but an implementation MUST
   correctly process these data items when correctly associated with a
   signal.

   The mandatory DLEP data items are:

   +------------+--------------------------------------+---------------+
   | Data Item  | Description                          | Section       |
   +------------+--------------------------------------+---------------+
   | TBD        | DLEP Version                         | Section 8.1   |
   | TBD        | Status                               | Section 8.2   |
   | TBD        | DLEP Port                            | Section 8.3   |
   | TBD        | Peer Type =TBD  |Length = 16                            | Modem Receive Window Value Section 8.4   |
   | TBD        | Heartbeat Interval                   | Section 8.5   |
   | TBD        | Extensions Supported                 | Section 8.6   |
   | TBD        | Experimental Definition              | Section 8.7   |
   | TBD        | MAC Address                          | Section 8.8   |
   | TBD        | IPv4 Address                         | Section 8.9   |
   | TBD        | IPv6 Address                         | Section 8.10  |
   | TBD        | IPv4 Attached Subnet                 | Section 8.11  |
   | TBD        | IPv6 Attached Subnet                 | Section 8.12  |
   | TBD        | Maximum Data Rate (Receive) MDRR)    | Section 8.13  |
   | TBD        | Maximum Data Rate (Transmit) (MDRT)  | Section 8.14  |
   | TBD        | Current Data Rate (Receive) (CDRR)   | Section 8.15  |
   | TBD        | Current Data Rate (Transmit) (CDRT)  | Section 8.16  |
   | TBD        | Latency                              | Section 8.17  |
   | TBD        | Resources (Receive) (RESR)           | Section 8.18  |
   | TBD        | Resources (Transmit) (REST)          | Section 8.19  |
   | TBD        | Relative Link Quality (Receive)      | Section 8.20  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Modem Receive Window Value            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (RLQR)                               |  Modem Receive Window Value               | Router Receive Window Value
   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ TBD        |                Router Receive Window Value Relative Link Quality (Transmit)     | Section 8.21  |
   |            | (RLQT)                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |  Router Receive Window Value
   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type                    - TBD

   Length                      - 16

   Modem Receive Window Value  - A 64-bit unsigned number, indicating
                                 the current (or initial) number of
                                 credits available on the Modem Receive
                                 Window.

   Router Receive Window Value - A 64-bit unsigned number, indicating
                                 the current (or initial) number of
                                 credits available on the Router Receive
                                 Window.

10.20  Credit Grant Request

   The Credit Grant Request TLV is an optional TLV. If credits are
   supported, the Credit Grant Request TLV is sent from a DLEP
   participant to grant an increment to credits on a window. The Credit
   Grant TLV is sent as a data item in either the Destination Up or
   Destination Update signals. The value in a Credit Grant TLV
   represents an increment to be added to any existing credits available
   on the window. Upon successful receipt and processing of a Credit
   Grant TLV, the receiver MUST respond with a signal containing a
   Credit Window Status TLV to report the updated aggregate values for
   synchronization purposes.

   In the Destination Up signal, when credits are desired, the
   originating peer MUST set the initial credit value of the window it
   controls (e.g. the Modem Receive Window, or Router Receive Window) to
   an initial, non-zero value. If the receiver of a Destination Up
   signal with a Credit Grant Request TLV supports credits, the receiver        | Link Characteristics ACK Timer       | Section 8.22  |
   +------------+--------------------------------------+---------------+

8.1.  DLEP Version

   The DLEP Version data item MUST either reject appear in the use of credits, via a Destination Up Peer Discovery
   (Section 7.1), Peer Offer (Section 7.2), Peer Initialization
   (Section 7.3) and Peer Initialization ACK
   response with the correct Status TLV, or set the initial value from
   the (Section 7.4) signals The
   Version data contained in item is used to indicate the Credit Window Status TLV. If version of the
   initialization completes successfully, protocol
   running in the receiver MUST respond originator.  A DLEP implementation MAY use this
   information to decide if the Destination Up signal with a Destination Up ACK signal that
   contains potential session partner is running at
   a Credit Window Status TLV, initializing its receive window. supported level.

   The Credit Grant TLV DLEP Version data item contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 4    |         Major Version         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Minor Version           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Data Item Type:  TBD

   Length:  4

   Major Version:  Major version of the DLEP protocol.

   Minor Version:  Minor version of the DLEP protocol.

   Support of this draft is indicated by setting the Major Version to
   '0', and the Minor Version to '8' (i.e., Version 0.8).

8.2.  Status

   The Status data item is MAY appear in the Peer Initialization ACK
   (Section 7.4), Peer Termination (Section 7.7), Peer Termination ACK
   (Section 7.8), Peer Update ACK (Section 7.6), Destination Up ACK
   (Section 7.10), Destination Down ACK (Section 7.12) and Link
   Characteristics ACK (Section 7.16) signals as part of an
   acknowledgement from either the modem or the router, to indicate the
   success or failure of the previously received signal.

   The Status data item contains the following fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 8 1    |       Credit Increment     Code      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1

   Status Code:  One of the codes defined below.

   +-------------------+-----------------------------------------------+
   |                      Credit Increment Status Code       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Reason                                        |      Credit Increment
   +-------------------+-----------------------------------------------+
   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type         - TBD
   Length           - 8

   Reserved         - A 64-bit unsigned number representing the
                      additional credits to be assigned to the credit
                      window. Since credits can only be granted Success           | The signal was processed successfully.        |
   | Unknown Signal    | The signal was not recognized by the
                      receiver on a window, the applicable credit window
                      (either the MRW          |
   |                   | implementation.                               |
   | Invalid Signal    | One or more data items in the RRW) is derived from the
                      sender of the grant. signal are      |
   |                   | invalid, unexpected or duplicated.            |
   | Unexpected Signal | The Credit Increment MUST NOT
                      cause the window to overflow; if this condition
                      occurs, implementations MUST set the credit window
                      to signal was not expected while the maximum value contained machine |
   |                   | was in this state, e.g., a 64-bit
                      quantity.

10.21  Credit Peer               |
   |                   | Initialization signal after session           |
   |                   | establishment.                                |
   | Request Denied    | The Credit Request TLV is an optional TLV. If credits are supported, receiver has not completed the Credit Request TLV MAY request.   |
   | Timed Out         | The request could not be sent from either DLEP participant, via
   a Destination Update signal, to indicate the desire for completed in the partner
   to grant additional credits     |
   |                   | time allowed.                                 |
   +-------------------+-----------------------------------------------+

8.3.  DLEP Port

   The DLEP Port data item MAY appear in order for the Peer Offer signal
   (Section 7.2).  The DLEP Port data transfer to proceed item indicates the TCP Port number
   on the session. DLEP server available for connections.  If provided, the corresponding Destination Up signal for
   receiver MUST use this
   session did NOT contain a Credit Window Status TLV, indicating that
   credits are information to be used on the session, then perform the Credit Request TLV
   MUST be rejected by TCP connect to the receiver via a Destination Update ACK signal.
   DLEP server.

   The Credit Request TLV DLEP Port data item contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Reserved, MUST|
   |               | Data Item Type| Length = 2    | be set to 0       TCP Port Number         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type     -
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length       - 1

   Reserved     - This field is currently unused and MUST be set to 0.

10.22

   Length:  2

   TCP Port Number:  TCP Port number on the DLEP Optional Signals Supported server.

8.4.  Peer Type

   The DLEP Optional Signals Supported TLV is a mandatory data item. If
   optional signals (e.g., the Link Characteristics Request Signal) are
   supported, they MUST be enumerated with this Peer Type data item inserted into MAY appear in both the Peer Initialization Discovery
   (Section 7.1) and Peer Initialization ACK Offer (Section 7.2) signals. Failure  The Peer Type
   data item is used by the router and modem to indicate optional signals indicates give additional
   information as to a receiving its type.  The peer that the
   sending implementation ONLY supports the core (mandatory) items
   listed in this specification. Optional signals that are NOT
   enumerated in this data item when issuing Peer Initialization or Peer
   Initialization ACK MUST NOT type is a string and is
   envisioned to be used during the DLEP session. for informational purposes (e.g., as output in
   a display command).

   The DLEP Optional Signals Supported TLV Peer Type data item contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 2 +   |List of optional signals ...
   | Data Item Type| Length = peer |               |number of opt. Peer Type                     |
   |               |               |signals.    type len   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type    -

   Data Item Type:  TBD

   Length:  Length      -  2 + the number of optional signals supported
   List        - peer type string.

   Peer Type:  UTF-8 encoded string.  For example, a satellite modem
      might set this variable to "Satellite terminal".

   An enumeration of the optional signal TLV Types
                  supported by implementation MUST NOT assume the implementation.

10.23  DLEP Optional Data Items Supported

   The DLEP Optional Data Items Supported TLV Peer Type is a mandatory data item.
   If optional data items (e.g., Resources) are supported, they MUST be
   enumerated with this NUL-terminated.

8.5.  Heartbeat Interval

   The Heartbeat Interval data item inserted into MUST appear in the Peer Discovery
   (Section 7.1), Peer Offer (Section 7.2), Peer Initialization
   (Section 7.3) and Peer Initialization ACK signals. Failure (Section 7.4) signals to
   indicate optional
   data items indicates the desired Heartbeat timeout window.  The receiver MUST
   either accept the timeout interval supplied by the sender, or reject
   the Peer Initialization, and close the socket.  Implementations MUST
   implement heuristics such that DLEP signals sent/received reset the
   timer interval.

   The Interval is used to specify a receiving peer that period (in seconds) for Heartbeat
   signals (Section 7.14).  By specifying an Interval value of 0,
   implementations MAY indicates the sending
   implementation ONLY supports desire to disable Heartbeat signals
   entirely (i.e., the core (mandatory) data items listed
   in this specification. Optional data items Interval is set to an infinite value), however,
   it is strongly recommended that are NOT listed in
   this data item implementations use non 0 timer
   values.

   A DLEP session will be considered inactive, and MUST NOT be used during the torn down, by
   an implementation detecting that two (2) Heartbeat intervals have
   transpired without receipt of any DLEP session. signals.

   The DLEP Optional Data Items Supported TLV Heartbeat Interval data item contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD  |Length = 2 +   |List of optional data items ...|
   |               |number of opt. |                               |
   |               |signals. Data Item Type| Length = 2    |           Interval            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type    -
   Data Item Type:  TBD

   Length      -

   Length:  2 + the number of optional data items supported
   List        -  An enumeration of the optional data item TLV Types
                  supported by the implementation.

10.24  DLEP Vendor Extension

   Interval:  0 = Do NOT use heartbeats on this peer-to-peer session.
      Non-zero = Interval, in seconds, for heartbeat signals.

8.6.  Extensions Supported

   The DLEP Vendor Extension Extensions Supported data item is an optional data item, and
   allows for vendor-defined information to MAY be passed between DLEP
   participants. The precise data carried used in both the payload portion of the Peer
   Initialization and Peer Initialization ACK signals.  The Extensions
   Supported data item is vendor-specific, however, used by the payload MUST adhere router and modem to a
   Type-Length-Value format. This negotiate
   additional optional data item is ONLY valid on
   Peer Initialization ACK, and if present, SHOULD contain device-
   specific information geared functionality they are willing to optimizing data transmission/reception
   over the modem's link. support.  The
   Extensions List is a concatenation of the types of each supported
   extension, found in the IANA DLEP Vendor Extension Data Item TLV Extensions repository.

   The Extensions Supported data item contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type = TBD
   | Data Item Type| Length        |OUI Length = No.  | Extensions List               | Vendor OUI...
   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |     OUI TLV Subtype   of values   | Payload...                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TLV Type        -

   Data Item Type:  TBD

   Length          - 3 + length

   Length:  Number of OUI (in octets) + payload length

   Vendor OUI      - The vendor OUI, Extensions supported.

   Extension List:  A list of extensions supported, identified by their
      1-octet value as specified listed in [IEEE]

   OUI TLV Subtype - A 16-bit quantity, intended to indicate the
             specific device.

   Payload         - Vendor-specific payload, formatted as Type, Length,
                     Value construct(s).

10.25  IPv4 Attached Subnet extensions registry.

8.7.  Experimental Definition

   The DLEP IPv4 Attached Subnet is an optional Experimental Definition data item, and allows a
   device to declare that it has an IPv4 subnet (e.g., a stub network)
   attached. If supported, item MAY be used in both the DLEP IPv4 Attached Subnet TLV Peer
   Initialization and Peer Initialization ACK signals.  The Experimental
   Definition data item is allowed
   ONLY in used by the DLEP "Destination Up" signal, router and MUST NOT appear more
   than once. All other occurrences of modem to indicate the DLEP IPv4 Attached Subnet TLV
   MUST
   formats to be treated as an error. Once an IPv4 Subnet has been declared used for experimental signals and data items for the
   given peer session.  The formats are identified by using a device, the declaration can NOT be withdrawn without terminating
   the destination (via string
   that matches the "Destination Down" signal) and re-issuing 'name' given to the "Destination Up" signal. experiment.

   The DLEP IPv4 Attached Subnet data Experimental Definition item TLV contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD
   | Data Item Type| Length = 5 len. | IPv4 Attached Subnet Experiment Name               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv4 Attached Subnet               |  Subnet Mask of Experiment |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     TLV Type     -                               |
   |               |      name     |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  Length       - 5

     IPv4 Subnet  - The IPv4 subnet reachable at the destination.

     Subnet Mask  - A subnet mask (0-32) to be applied to of the IPv4
                    subnet.

10.26  IPv6 Attached Subnet

   The DLEP IPv6 Attached Subnet is an optional data item, and allows a
   device to declare that it has an IPv6 subnet (e.g., a stub network)
   attached. If supported, name string for the DLEP IPv6 Attached Subnet TLV is allowed
   ONLY in Experiment.

   Experiment Name:  UTF-8 encoded string, containing the DLEP "Destination Up" signal, and MUST NOT appear more
   than once. All other occurrences name of the DLEP IPv6 Attached Subnet TLV
      experiment being utilized.

   An implementation receiving this data item MUST be treated as an error. As in compare the case received
   string to a list of the IPv4 attached
   subnet, once an IPv6 attached subnet has been declared, experiments that it can supports.  An implementation
   MUST NOT be
   withdrawn without terminating assume the destination (via "Destination
   Down") Experiment Name is NUL-terminated.

8.8.  MAC Address

   The MAC address data item MUST appear in all destination-oriented
   signals (i.e., Destination Up (Section 7.9), Destination Up ACK
   (Section 7.10), Destination Down (Section 7.11), Destination Down ACK
   (Section 7.12), Destination Update (Section 7.13), Link
   Characteristics Request (Section 7.15), and re-issuing the "Destination Up" signal. Link Characteristics ACK
   (Section 7.16)).  The DLEP IPv6 Attached Subnet MAC Address data item TLV contains the following
   fields: address of
   the destination on the remote node.  The MAC address MAY be either a
   physical or a virtual destination.  Examples of a virtual destination
   would be a multicast MAC address, or the broadcast MAC
   (FF:FF:FF:FF:FF:FF).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TLV Type =TBD   |Length = 17    | IPv6 Attached Subnet         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv6 Attached Subnet
   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Data Item Type| Length = 6    |      IPv6 Attached Subnet          MAC Address          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv6 Attached Subnet                      MAC Address                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv6 Attached Subnet      | Subnet Mask  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     TLV Type     -

   Data Item Type:  TBD

     Length       - 17

   Length:  6

   MAC Address:  MAC Address of the destination (either physical or
      virtual).

8.9.  IPv4 Subnet  - Address

   The IPv6 subnet reachable at IPv4 Address data item MUST appear in the Peer Offer signal
   (Section 7.2), and MAY appear in the Peer Update (Section 7.5),
   Destination Up (Section 7.9) and Destination Update (Section 7.13)
   signals.  When included in Destination signals, this data item
   contains the IPv4 address of the destination.

     Subnet Mask  - A subnet mask (0-128) to be applied to  In the IPv6
              subnet.

11. DLEP Protocol Signals

   DLEP signals are encoded as a string Peer Offer
   signal, it contains the IPv4 address of Type-Length-Value (TLV)
   constructs. The first TLV in a DLEP signal MUST the originating peer to be
   used to establish a valid DLEP
   signal, as defined in section 11.1 session.  In either case, the data item also
   contains an indication of whether this document. Following the
   signal TLV is 0 a new or more TLVs, representing the data items that are
   appropriate for the signal. The layout existing address,
   or is a deletion of a DLEP previously known address.  When used in a Peer
   Offer signal is thus: the Add/Drop Indicator MUST be 1 (i.e.  Add).

   The IPv4 Address data item contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | DLEP Signal   |DLEP Signal length (length of  |Start of DLEP Data Item Type| Length = 5    |   Add/Drop    | Type value    |all data items)                |data item TLVs IPv4 Address  |
   | (value TBD)               |               |   Indicator   |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All DLEP signals begin with this structure. Therefore, in the
   following descriptions of specific signals, this header structure is
   assumed, and will not be replicated.

11.1  Signal TLV Values

   As mentioned above, all DLEP signals begin with the Type value. Valid
   DLEP signals are:

          TLV      TLV
          Value    Description
          =========================================
          TBD      Peer Discovery
          TBD      Peer Offer
          TBD      Peer Initialization
          TBD      Peer Update
          TBD      Peer Update ACK
          TBD      Peer Termination
          TBD      Peer Termination ACK
          TBD      Destination Up
          TBD      Destination Up ACK
          TBD      Destination Down
          TBD      Destination Down ACK
          TBD      Destination Update
          TBD      Heartbeat
          TBD      Link Characteristics Request
   |            IPv4 Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD      Link Characteristics ACK

11.2 Peer Discovery Signal

   The Peer Discovery Signal

   Length:  5

   Add/Drop:  Value indicating whether this is sent by a router to discover DLEP
   routers in the network. The Peer Offer signal is required to complete
   the discovery process. Implementations MAY implement their own retry
   heuristics in cases where it is determined the Peer Discovery Signal
   has timed out.

   To construct new or existing address
      (1), or a Peer Discovery signal, the initial TLV Type value is
   set to DLEP_PEER_DISCOVERY (value TBD). withdrawal of an address (0).

   IPv4 Address:  The signal TLV MUST be
   followed by the mandatory Data Item TLVs.

   Mandatory Data Item TLVs:
              - DLEP Version
              - Heartbeat Interval
   There are NO optional data items for IPv4 address of the Peer Discovery signal.

11.3 Peer Offer Signal destination or peer.

8.10.  IPv6 Address

   The IPv6 Address data item MUST appear in the Peer Offer Signal is sent by a DLEP modem signal
   (Section 7.2), and MAY appear in response to a the Peer
   Discovery Signal. Upon receipt, Update (Section 7.5),
   Destination Up (Section 7.9) and processing, Destination Update (Section 7.13)
   signals.  When included in Destination signals, this data item
   contains the IPv6 address of a the destination.  In the Peer Offer
   signal, it contains the router responds by issuing a TCP connect to the
   address/port combination specified in IPv6 address of the received Peer Offer.

   The Peer Offer signal MUST originating peer to be sent
   used to establish a DLEP session.  In either case, the unicast address data item also
   contains an indication of the
   originator whether this is a new or existing address,
   or is a deletion of Peer Discovery.

   To construct a previously known address.  When used in a Peer
   Offer signal, signal the initial TLV type value is set
   to DLEP_PEER_OFFER (value TBD). Add/Drop Indicator MUST be 1 (i.e.  Add).

   The signal TLV is then followed by
   all mandatory Data Item TLVs, then by any optional Data Item TLVs IPv6 Address data item contains the
   implementation supports:

   Mandatory following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item TLVs:
              - DLEP Version
              - Heartbeat Interval
              - At least one (1) IPv4 or Type| Length = 17   |   Add/Drop    | IPv6 Address  |
   |               |               |   Indicator   |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                IPv6 Address TLV
              - DLEP Port

   Optional                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item TLVs:
              - Peer Type
              - Status

11.4 Peer Initialization Signal

   The Peer Initialization signal Type:  TBD

   Length:  17

   Add/Drop:  Value indicating whether this is sent by a router to start new or existing address
      (1), or a withdrawal of an address (0).

   IPv6 Address:  IPv6 Address of the destination or peer.

8.11.  IPv4 Attached Subnet

   The DLEP
   TCP session. It is sent by the router after IPv4 Attached Subnet allows a TCP connect device to an
   address/port combination declare that was obtained either via receipt of it has
   an IPv4 subnet (e.g., a
   Peer Offer, or from a-priori configuration. If any optional signals
   or data items are supported by stub network) attached.  Once an IPv4 Subnet
   has been declared on a device, the implementation, they MUST declaration can NOT be
   enumerated in withdrawn
   without terminating the DLEP Optional Signals Supported destination (via the Destination Down signal)
   and re-issuing the Destination Up signal.

   The DLEP Optional
   Data Items Supported items.

   Mandatory Data Item TLVs:
               - DLEP Version
               - Heartbeat Interval
               - Optional Signals Supported
               - Optional Data Items Supported
   Optional Data IPv4 Attached Subnet data item data item contains the
   following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Data Item TLVs:
              - Peer Type
   If the Optional Signals Supported (or the Optional | Length = 5    | IPv4 Attached Subnet          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv4 Attached Subnet     | Subnet Mask   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Items
   Supported) TLV is absent in Peer Initialization, the receiver of Item Type:  TBD

   Length:  5

   IPv4 Subnet:  The IPv4 subnet reachable at the
   signal MUST conclude that there is NO optional support in destination.

   Subnet Mask:  A subnet mask (0-32) to be applied to the
   sender.

11.5 Peer Initialization ACK Signal IPv4 subnet.

8.12.  IPv6 Attached Subnet

   The Peer Initialization ACK signal is DLEP IPv6 Attached Subnet allows a mandatory signal, sent in
   response device to declare that it has
   an IPv6 subnet (e.g., a received Peer Initialization signal. The Peer
   Initialization ACK signal completes the TCP-level DLEP session
   establishment; stub network) attached.  As in the sender case of
   the signal should transition to IPv4 attached Subnet data item above, once an "in-
   session" state when IPv6 attached
   subnet has been declared, it can NOT be withdrawn without terminating
   the signal is sent, destination (via Destination Down) and re-issuing the receiver should
   transition to the "in-session" state upon receipt (and successful
   parsing) of Peer Initialization ACK.

   All supported metric Destination
   Up signal.

   The DLEP IPv6 Attached Subnet data items MUST be included in the Peer
   Initialization ACK signal, with default values to be used on a
   "modem-wide" basis. This can be viewed as item data item contains the modem "declaring" all
   supported metrics
   following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 17   | IPv6 Attached Subnet          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv6 Attached Subnet                                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv6 Attached Subnet                                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv6 Attached Subnet                                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv6 Attached Subnet     | Subnet Mask   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  17

   IPv4 Subnet:  The IPv6 subnet reachable at DLEP session initialization. Receipt of any DLEP
   signal containing a metric data item NOT included in Peer
   Initialization ACK MUST the destination.

   Subnet Mask:  A subnet mask (0-128) to be treated as an error, resulting in
   termination of applied to the DLEP session between router and modem. If optional
   signals and/or IPv6 subnet.

8.13.  Maximum Data Rate (Receive)

   The Maximum Data Rate (Receive) (MDRR) data items are supported by the modem, they item MUST be
   enumerated appear in the DLEP Optional Signals supported and DLEP Optional
   data items supported TLVs.

   The
   Peer Initialization ACK signal (Section 7.4), and MAY contain the DLEP Vendor
   Extension data item, as documented appear in section 10.22

   After the
   Peer Initialization/Peer Initialization ACK signals have
   been successfully exchanged, implementations SHOULD only utilize
   options that are supported in BOTH peers (e.g. router Update (Section 7.5), Destination Up (Section 7.9) and modem). Any
   attempt by a DLEP session peer to send an optional signal
   Destination Update (Section 7.13) signals to a peer
   without support MUST result in an error which terminates indicate the session.
   Any optional maximum
   theoretical data item sent to a peer without support will rate, in bits per second, that can be ignored
   and silently dropped.

   To construct a Peer Initialization ACK signal, achieved while
   receiving data on the initial TLV type
   value is set to DLEP_PEER_INIT_ACK (value TBD). link.

   The signal TLV is
   then followed by the required Maximum Data Rate (Receive) data items:

   Mandatory item contains the following
   fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 8    |          MDRR (bps)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        MDRR (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           MDRR (bps)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item TLVs:
               - DLEP Version
               - Heartbeat Interval
               - Type:  TBD

   Length:  8

   Maximum Data Rate Receive
               - (Receive):  A 64-bit unsigned integer, representing
      the maximum theoretical data rate, in bits per second (bps), that
      can be achieved while receiving on the link.

8.14.  Maximum Data Rate Transmit
               - Current Data Rate Receive
               - Current (Transmit)

   The Maximum Data Rate Transmit
               - DLEP Optional Signals Supported
               - DLEP Optional Data Items Supported
               - Status
   Optional Data Item TLVs:
               - Peer Type
               - DLEP Vendor Extension
               - Latency
               - Relative Link Quality Receive
               - Relative Link Quality Transmit
               - Resources (Receive)
               - Resources (Transmit)

11.6 Peer Update Signal

   The (MDRT) data item MUST appear in the
   Peer Update Initialization ACK signal is an optional signal, sent by a DLEP peer to
   indicate local Layer 3 address changes, or for metric changes on a
   modem-wide basis. For example, addition of an IPv4 address to the
   router (Section 7.4), and MAY prompt a appear in the
   Peer Update signal (Section 7.5), Destination Up (Section 7.9) and
   Destination Update (Section 7.13) signals to its attached DLEP modems.
   Also, a modem indicate the maximum
   theoretical data rate, in bits per second, that changes its can be achieved while
   transmitting data on the link.

   The Maximum Data Rate (Transmit) data item contains the following
   fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 8    |          MDRT (bps)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        MDRT (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           MDRT (bps)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  8

   Maximum Data Rate for all destinations
   MAY reflect that change via a Peer Update Signal to its attached
   router(s).

   Concerning Layer 3 addresses, if the modem is capable of
   understanding and forwarding this information (via proprietary
   mechanisms), (Transmit):  A 64-bit unsigned integer,
      representing the address update would prompt any remote DLEP modems
   (DLEP-enabled modems maximum theoretical data rate, in a remote node) to issue a "Destination
   Update" signal to their local routers with the new (or deleted)
   addresses. Modems bits per second
      (bps), that do not track Layer 3 addresses SHOULD silently
   parse and ignore can be achieved while transmitting on the Peer Update Signal. Modems that track Layer 3
   addresses link.

8.15.  Current Data Rate (Receive)

   The Current Data Rate (Receive) (CDRR) data item MUST acknowledge appear in the
   Peer Update with a Initialization ACK signal (Section 7.4), and MAY appear in the
   Peer Update (Section 7.5), Destination Up (Section 7.9), Destination
   Update (Section 7.13), Link Characteristics Request (Section 7.15)
   and Link Characteristics ACK
   signal. Routers (Section 7.16) signals to indicate the
   rate at which the link is currently operating for receiving a Peer Update with metric changes MUST
   apply traffic.
   When used in the new metric to all destinations (remote nodes) accessible
   via Link Characteristics Request signal, CDRR represents
   the desired receive rate, in bits per second, on the link.

   The Current Data Rate (Receive) data item contains the following
   fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 8    | CDRR (bps)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        CDRR (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        CDRR (bps)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  8

   Current Data Rate (Receive):  A 64-bit unsigned integer, representing
      the modem. Supporting implementations are free to employ
   heuristics to retransmit Peer Update signals. The sending of Peer
   Update Signals for Layer 3 address changes SHOULD cease when a either
   participant (router or modem) determines current data rate, in bits per second, that is currently be
      achieved while receiving traffic on the other
   implementation does NOT support Layer 3 address tracking. link.

   If metrics are supplied with the Peer Update signal (e.g. Maximum
   Data Rate), these metrics are considered to be modem-wide, there is no distinction between current and
   therefore maximum receive data
   rates, current data rate receive MUST be applied set equal to all destinations the maximum
   data rate receive.

8.16.  Current Data Rate (Transmit)

   The Current Data Rate Receive (CDRT) data item MUST appear in the information base
   associated with
   Peer Initialization ACK signal (Section 7.4), and MAY appear in the router/modem session.

   To construct a
   Peer Update signal, (Section 7.5), Destination Up (Section 7.9), Destination
   Update (Section 7.13), Link Characteristics Request (Section 7.15)
   and Link Characteristics ACK (Section 7.16) signals to indicate the initial TLV type value
   rate at which the link is set
   to DLEP_PEER_UPDATE (value TBD). currently operating for transmitting
   traffic.  When used in the Link Characteristics Request signal, CDRT
   represents the desired transmit rate, in bits per second, on the
   link.

   The Signal TLV is followed by any
   OPTIONAL Current Data Rate (Transmit) data item contains the following
   fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item TLVs.

   Optional Type| Length = 8    | CDRT (bps)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        CDRT (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        CDRT (bps)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item TLVs:
              - IPv4 Address
              - IPv6 Address
              - Maximum Data Rate (Receive)
              - Maximum Data Rate (Transmit)
              - Current Data Rate (Receive)
              - Type:  TBD

   Length:  8

   Current Data Rate (Transmit)
              - Latency
              - Resources (Receive)
              - Resources (Transmit)
              - Relative Link Quality (Receive)
              - Relative Link Quality (Transmit)

11.7 Peer Update ACK Signal

   The Peer Update ACK signal is an optional signal, and is sent by
   implementations supporting Layer 3 address tracking and/or modem-wide
   metrics to indicate whether a Peer Update Signal was successfully
   processed. If (Transmit):  A 64-bit unsigned integer,
      representing the Peer Update ACK is issued, it MUST contain a Status current data item, indicating the success or failure of processing the
   received Peer Update.

   To construct a Peer Update ACK signal, rate, in bits per second, that is
      currently be achieved while transmitting traffic on the initial TLV type value link.

   If there is no distinction between current and maximum transmit data
   rates, current data rate transmit MUST be set equal to DLEP_PEER_UPDATE_ACK (value TBD). the maximum
   data rate transmit.

8.17.  Latency

   The Status Latency data item TLV is
   placed in the packet next, completing the Peer Update ACK.

   Mandatory Data Item TLVs:

             - Status

   Note that there are NO optional data item TLVs specified for this
   signal.

11.8 Peer Termination Signal

   The Peer Termination Signal is sent by a DLEP participant when MUST appear in the
   router/modem session needs to be terminated. Implementations
   receiving a Peer Termination
   Initialization ACK signal MUST send a (Section 7.4), and MAY appear in the Peer Termination
   Update (Section 7.5), Destination Up (Section 7.9), Destination
   Update (Section 7.13), Link Characteristics Request (Section 7.15)
   and Link Characteristics ACK
   signal (Section 7.16) signals to confirm indicate the termination process. The sender
   amount of a Peer
   Termination signal is free to define its heuristics latency, in event of a
   timeout. The receiver of a Peer Termination Signal MUST release all
   resources allocated for microseconds, on the router/modem session, and MUST eliminate
   all destinations link, or in the information base accessible via the
   router/modem pair represented by case of
   the session. Router and modem state
   machines are returned Link Characteristics Request, to indicate the "discovery" state. No Destination Down
   signals are sent.

   To construct a Peer Termination signal, maximum latency
   required on the initial TLV type link.

   The Latency value is
   set to DLEP_PEER_TERMINATION (value TBD). reported as delay.  The signal TLV calculation of latency
   is followed
   by any OPTIONAL implementation dependent.  For example, the latency may be a
   running average calculated from the internal queuing.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item TLVs the implementation supports:

   Optional Type| Length = 4    | Latency in microseconds       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Latency (cont.) microsecs    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Data Item TLVs:

             - Status

11.9 Type:  TBD

   Length:  4

   Latency:  A 32-bit unsigned value, representing the transmission
      delay that a packet encounters as it is transmitted over the link.

8.18.  Resources (Receive)

   The Resources (Receive) (RESR) data item MAY appear in the Peer Termination
   Initialization ACK Signal

   The signal (Section 7.4), Peer Termination Signal Update (Section 7.5),
   Destination Up (Section 7.9), Destination Update (Section 7.13) and
   Link Characteristics ACK is sent by a DLEP peer in response (Section 7.16) signals to
   a received Peer Termination order. Receipt indicate the
   amount of a Peer Termination ACK
   signal completes recources for reception (with 0 meaning 'no resources
   available', and 100 meaning 'all resources available') at the teardown
   destination.  The list of resources that might be considered is
   beyond the router/modem session.

   To construct a Peer Termination ACK signal, the initial TLV type
   value scope of this document, and is set left to DLEP_PEER_TERMINATION_ACK (value TBD). implementations to
   decide.

   The
   Identification Resources (Receive) data item TLV is placed in the packet next, followed
   by any OPTIONAL TLVs contains the implementation supports:

   Optional following fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item TLVs:

             - Status

11.10 Destination Up Signal Type| Length = 1    |     RESR      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1

   Resources (Receive):  A DLEP participant sends percentage, 0-100, representing the Destination Up signal amount of
      resources allocated to report that receiving data.

   If a
   new destination has been detected. A Destination Up device cannot calculate RESR, this data item SHOULD NOT be
   issued.

8.19.  Resources (Transmit)

   The Resources (Receive) (RESR) data item MAY appear in the Peer
   Initialization ACK Signal is
   required to confirm a received Destination Up. A signal (Section 7.4), Peer Update (Section 7.5),
   Destination Up
   signal can be sent either by the modem, (Section 7.9), Destination Update (Section 7.13) and
   Link Characteristics ACK (Section 7.16) signals to indicate the
   amount of recources for transmission (with 0 meaning 'no resources
   available', and 100 meaning 'all resources available') at the
   destination.  The list of resources that a new remote
   node has been detected, or by might be considered is
   beyond the router, scope of this document, and is left to indicate implementations to
   decide.

   The Resources (Transmit) data item contains the following fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 1    |     REST      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1

   Resources (Transmit):  A percentage, 0-100, representing the presence amount
      of resources allocated to transmitting data.

   If a new logical destination (e.g., a Multicast group) exists in the
   network. device cannot calculate REST, this data item SHOULD NOT be
   issued.

8.20.  Relative Link Quality (Receive)

   The sender of Relative Link Quality (Receive) (RLQR) data item MAY appear in
   the Peer Initialization ACK signal (Section 7.4), Peer Update
   (Section 7.5), Destination Up Signal is free to define its retry
   heuristics in event of a timeout. When a (Section 7.9), Destination Up signal is
   received Update
   (Section 7.13) and successfully parsed, the receiver should add knowledge
   of the new destination Link Characteristics ACK (Section 7.16) signals to its information base, indicating that
   indicate the
   destination is accessible via quality of the modem/router pair.

   To construct a Destination Up signal, link for receiving data as calculated by
   the initial TLV type value is
   set to DLEP_DESTINATION_UP (value TBD). originating peer.

   The MAC Address Relative Link Quality (Receive) data item TLV
   is placed in contains the packet next, followed by any supported optional following
   fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item TLVs into the packet:

   Optional Type| Length = 1    |     RLQR      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item TLVs:

              - IPv4 Address
              - IPv6 Address
              - Maximum Data Rate (Receive)
              - Maximum Data Rate (Transmit)
              - Current Data Rate (Receive)
              - Current Data Rate (Transmit)
              - Latency
              - Resources (Receive)
              - Resources (Transmit)
              - Type:  TBD

   Length:  1

   Relative Link Quality (Receive):  A non-dimensional integer, 1-100,
      representing relative link quality.  A value of 100 represents a
      link of the highest quality.

   If a device cannot calculate the RLQR, this data item SHOULD NOT be
   issued.

8.21.  Relative Link Factor (Receive)
              - Quality (Transmit)

   The Relative Link Factor Quality (Transmit)
              - Credit Window Status
              - IPv4 Attached Subnet
              - IPv6 Attached Subnet

11.11 Destination Up ACK Signal

   A DLEP participant sends (RLQT) data item MAY appear in
   the Peer Initialization ACK signal (Section 7.4), Peer Update
   (Section 7.5), Destination Up (Section 7.9), Destination Update
   (Section 7.13) and Link Characteristics ACK Signal (Section 7.16) signals to
   indicate
   whether the quality of the link for transmitting data as calculated
   by the originating peer.

   The Relative Link Quality (Transmit) data item contains the following
   fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 1    |     RLQT      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1

   Relative Link Quality (Transmit):  A non-dimensional integer, 1-100,
      representing relative link quality.  A value of 100 represents a Destination Up Signal was successfully processed.

   To construct
      link of the highest quality.

   If a Destination Up ACK signal, device cannot calculate the initial TLV type value
   is set to DLEP_DESTINATION_UP_ACK (value TBD). RLQT, this data item SHOULD NOT be
   issued.

8.22.  Link Characteristics ACK Timer

   The MAC Address Link Characteristics ACK Timer data item TLV is placed MAY appear in the packet next, containing Link
   Characterisitics Request signal (Section 7.15) to indicate the MAC address
   desired number of seconds to the DLEP destination. sender will wait for a response to
   the request.  If this data item is omitted, implementations
   supporting the Link Characteristics Request SHOULD choose a default
   value.

   The implementation would then place any
   supported optional Link Characteristics ACK Timer data item contains the following
   fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item TLVs into the packet:

   Optional Type| Length = 1    | Interval      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item TLVs:
              - Credit Window Status

11.12 Destination Down Signal

   A DLEP peer sends the Destination Down signal Type:  TBD
   Length:  1

   Interval:  0 = Do NOT use timeouts for Link Characteristics requests
      on this router/modem session.  Non-zero = Interval, in seconds, to report when a
   destination (a remote node or
      wait before considering a multicast group) is no longer
   reachable. The Destination Down signal MUST contain Link Characteristics Request has been
      lost.

9.  Credit-Windowing

   DLEP includes an OPTIONAL credit-windowing scheme analogous to the MAC Address
   data item TLV. Other TLVs
   one documented in [RFC5578].  In this scheme, traffic between the
   router and modem is treated as listed are OPTIONAL, two unidirectional windows.  This
   document identifies these windows as the 'Modem Receive Window', or
   MRW, and MAY be present
   if an implementation supports them. A Destination Down ACK Signal the 'Router Receive Window', or RRW.

   If the OPTIONAL credit-windowing scheme is used, credits MUST be sent
   granted by the recipient of receiver on a Destination Down signal to confirm given window - that is, on the relevant 'Modem
   Receive Window' (MRW), the modem is responsible for granting credits
   to the router, allowing it (the router) to send data has been removed from to the information base.
   The sender of modem.
   Likewise, the Destination Down signal router is free responsible for granting credits on the RRW,
   which allows the modem to define its retry
   heuristics send data to the router.

   DLEP expresses all credit data in event number of octets.  The total number
   of credits on a timeout.

   To construct a Destination Down signal, window, and the initial TLV type value is
   set increment to DLEP_DESTINATION_DOWN (value TBD). The signal TLV is followed
   by the mandatory MAC Address data item TLV.

   Note add to a grant, are
   always expressed as a 64-bit unsigned integer quantity.

   If used, credits are managed on a neighbor-specific basis; that there is,
   separate credit counts are NO OPTIONAL data item TLVs maintained for this signal.

11.13 Destination Down ACK Signal

   A DLEP participant sends each neighbor requiring the Destination Down ACK Signal
   service.  Credits do not apply to indicate
   whether a received Destination Down Signal was successfully
   processed. If successfully processed, the sender of DLEP session that exists
   between routers and modems.

   If a peer is able to support the ACK OPTIONAL credit-windowing scheme
   then it MUST have
   removed all entries include a Extensions Supported data item (Section 8.6)
   including the value DLEP_EXT_CREDITS (value TBD) in the information base appropriate
   Peer Initialization or Peer Initialization ACK signal.

9.1.  Credit-Windowing Signals

   The credit-windowing scheme introduces no additional DLEP signals.
   However, if a peer has advertised during session initialization that pertain to
   it supports the
   referenced destination. As with credit-windowing scheme then the following DLEP
   signals may contain additional credit-windowing data items:

9.1.1.  Destination Down signal, there
   are NO OPTIONAL Data Item TLVs defined for Up Signal

   The Destination Up signal MAY contain one of each of the following
   data items:

   o  Credit Grant (Section 9.2.2)

9.1.2.  Destination Down Up ACK
   signal.

   To construct a Signal

   The Destination Down signal, Up ACK signal MAY contain one of each of the initial TLV type value is
   set to DLEP_DESTINATION_DOWN_ACK (value TBD). The mandatory
   following data item
   TLVs follow:

      - MAC Address Data item
      - items:

   o  Credit Window Status data item

11.14 (Section 9.2.1)

9.1.3.  Destination Update Signal

   A DLEP participant sends the

   The Destination Update signal when it
   detects some change in the information base for a given destination
   (remote node or multicast group). Some examples MAY contain one of each of changes that would
   prompt a Destination Update signal are:

       - Change in link metrics (e.g., Data Rates)
       - Layer 3 addressing change (for implementations that support it)

   To construct a Destination Update signal, the initial TLV type value
   is set to DLEP_DESTINATION_UPDATE (value TBD). Following the signal
   TLV are the mandatory Data Item TLVs:

   MAC Address
   following data item TLV

   After placing the mandatory items:

   o  Credit Window Status (Section 9.2.1)

   o  Credit Grant (Section 9.2.2)

   o  Credit Request (Section 9.2.3)

9.2.  Credit-Windowing Data Items

   The credit-windowing scheme introduces 3 additional data item TLV into items.  If a
   peer has advertised during session initialization that it supports
   the packet, credit-windowing scheme then it MUST correctly process the
   implementation would place any supported OPTIONAL data item TLVs.
   Possible OPTIONAL
   following data item TLVs are:

              - IPv4 Address
              - IPv6 Address
              - Maximum Data Rate (Receive)
              - Maximum Data Rate (Transmit)
              - Current Data Rate (Receive)
              - Current items without error.

          +------------+-----------------------+----------------+
          | Data Rate (Transmit)
              - Latency
              - Resources (Receive)
              - Resources (Transmit)
              - Relative Link Quality (Receive)
              - Relative Link Quality (Transmit)
              - Item  | Description           | Section        |
          +------------+-----------------------+----------------+
          | TBD        | Credit Window Status
              -  | Section 9.2.1  |
          | TBD        | Credit Grant
              -          | Section 9.2.2  |
          | TBD        | Credit Request

11.15 Heartbeat Signal

   A Heartbeat Signal is sent by a DLEP participant every N seconds,
   where N is defined in the "Heartbeat Interval" field of the Peer
   Initialization signal. Note that implementations setting the
   Heartbeat Interval to 0 effectively set        | Section 9.2.3  |
          +------------+-----------------------+----------------+

9.2.1.  Credit Window Status

   If the interval to an infinite
   value, therefore, in those cases, this signal would NOT be sent.

   The signal credit-window scheme is used supported by participants to detect when a DLEP session
   partner (either the modem or the router) is no longer communicating.
   Participants SHOULD allow two (2) heartbeat intervals to expire with
   no traffic on the router/modem session before initiating DLEP session
   termination procedures.

   To construct a Heartbeat signal, participants
   (both the initial TLV type value is set to
   DLEP_PEER_HEARTBEAT (value TBD). The signal TLV is followed by router and the
   mandatory Heartbeat Interval/Threshold data item.

   Note that there are NO OPTIONAL modem), the Credit Window Status data item TLVs for this signal.

11.16 Link Characteristics Request Signal

   The Link Characteristics Request Signal is an optional signal, and is
   MUST be sent by the router to request that participant receiving a Credit Grant for a given
   destination.

   The Credit Window Status data item contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type| Length = 16   | Modem Receive Window Value    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Modem Receive Window Value                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Modem Receive Window Value   | Router Receive Window Value   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Router Receive Window Value                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Router Receive Window Value  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  16

   Modem Receive Window Value:  A 64-bit unsigned integer, indicating
      the current (or initial) number of credits available on the Modem
      Receive Window.

   Router Receive Window Value:  A 64-bit unsigned integer, indicating
      the modem initiate changes for
   specific characteristics current (or initial) number of credits available on the link. Router
      Receive Window.

9.2.2.  Credit Grant

   The request can reference
   either a real (e.g., a remote node), or Credit Grant data item is sent from a logical (e.g., DLEP participant to grant
   an increment to credits on a multicast
   group) destination within window.  The Credit Grant data item MAY
   appear in the network. Destination Up (Section 7.9) or Destination Update
   (Section 7.13) signals.  The Link Characteristics Request signal contains either value in a Current
   Data Rate (CDRR or CDRT) TLV Credit Grant data item
   represents an increment to request a different datarate than
   what is currently allocated, a Latency TLV be added to request that traffic
   delay any existing credits available
   on the link not exceed window.  Upon successful receipt and processing of a Credit
   Grant data item, the specified value, or both. A Link
   Characteristics ACK Signal is required receiver MUST respond with a signal containing a
   Credit Window Status data item to complete report the request.
   Implementations updated aggregate values
   for synchronization purposes.

   In the Destination Up signal, when credits are free desired, the
   originating peer MUST set the initial credit value of the window it
   controls (i.e., the Modem Receive Window, or Router Receive Window)
   to define their retry heuristics in event an initial, non-zero value.  If the receiver of a timeout. Issuing a Link Characteristics Request Destination Up
   signal with ONLY the MAC
   Address TLV is a mechanism a peer MAY use to request metrics (via Credit Grant data item supports credits, the
   Link Characteristics ACK) from its partner.

   To construct receiver
   MUST either reject the use of credits, via a Destination Up ACK
   response containing a Link Characteristics Request signal, Status data item (Section 8.2) with a status
   code of 'Request Denied', or set the initial TLV
   type value is set to DLEP_Destination_LINK_CHAR_REQ (value TBD).
   Following the signal TLV is from the mandatory Data Item TLV:

   MAC Address data item TLV

   After placing
   contained in the mandatory Credit Window Status data item TLV into item.  If the packet,
   initialization completes successfully, the
   implementation would place any supported OPTIONAL receiver MUST respond to
   the Destination Up signal with a Destination Up ACK signal that
   contains a Credit Window Status data item TLVs.
   Possible optional item, initializing its receive
   window.

   The Credit Grant data item TLVs are:

   Current contains the following fields:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Rate  -  If present, this value represents Item Type| Length = 8    |       Credit Increment        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Credit Increment                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Credit Increment         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  8

   Reserved:  A 64-bit unsigned integer representing the NEW (or
                         unchanged, if additional
      credits to be assigned to the request credit window.

   Since credits can only be granted by the receiver on a window, the
   applicable credit window (either the MRW or the RRW) is denied) Current
                         Data Rate in bits per second (bps).

   Latency            -  If present, derived from
   the sender of the grant.  The Credit Increment MUST NOT cause the
   window to overflow; if this value represents condition occurs, implementations MUST
   set the maximum
                         desired latency (e.g., it is a not-to-exceed
                         value) in microseconds on credit window to the link.

11.17 Link Characteristics ACK Signal maximum value contained in a 64-bit
   quantity.

9.2.3.  Credit Request

   The LInk Characteristics ACK signal is an optional signal, and is Credit Request data item MAY be sent by modems supporting it to from either DLEP
   participant, via the router letting Destination Update signal (Section 7.13), to
   indicate the router know desire for the success or failure of a requested change partner to grant additional credits in link characteristics.
    The Link Characteristics ACK
   order for data transfer to proceed on the session.  If the
   corresponding Destination Up signal SHOULD (Section 7.9) for this session
   did NOT contain a complete set of
   metric Credit Window Status data item TLVs. It MUST contain the same TLV types as item, indicating that
   credits are to be used on the
   request. The values in session, then the metric Credit Request data
   item TLVs in the Link
   Characteristics ACK signal MUST reflect the link characteristics
   after be rejected by the request has been processed.

   To construct receiver via a Link Characteristics Request Destination Update ACK signal, the initial
   TLV type value is set to DLEP_Destination_LINK_CHAR_ACK (value TBD).
   Following the
   signal TLV is the mandatory Data Item TLV:

   MAC Address containing a Status data item TLV

   After placing the mandatory (Section 8.2) with status code
   'Request Denied'.

   The Credit Request data item TLV into the packet, contains the
   implementation would place any supported OPTIONAL data item TLVs.
   Possible OPTIONAL data item TLVs are:

   Current following fields:

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Rate  -  If present, this value represents the requested
                         data rate in bits per second (bps).

   Latency            -  If present, this value represents the NEW
                         maximum latency (or unchanged, if the request Item Type| Length = 1    | Reserved, MUST|
   |               |               | be set to 0   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1

   Reserved:  This field is denied), expressed in microseconds, on the
                         link.

12. currently unused and MUST be set to 0.

10.  Security Considerations

   The protocol does not contain any mechanisms for security (e.g. (e.g.,
   authentication or encryption).  The protocol assumes that any
   security would be implemented in the underlying transport (for
   example, by use of DTLS or some other mechanism), and is therefore
   outside the scope of this document.

13.

11.  IANA Considerations

   This section specifies requests to IANA.

13.1

11.1.  Registrations

   This specification defines:

   o  A new repository for DLEP signals, with fifteen sixteen values currently
      assigned.

   o  Reservation of numbering space for Experimental DLEP signals.

   o  A new repository for DLEP Data Items, data items, with twenty-one twenty-three values
      currently assigned.

   o  Reservation of numbering space in the Data Items data items repository for
      experimental data items.

   o  A new repository for DLEP status codes.

   o  A new repository for DLEP extensions, with one value currently
      assigned.

   o  A request for allocation of a well-known port for DLEP
      communication.

   o  A request for allocation of a multicast address for DLEP
      discovery.

13.2

11.2.  Expert Review: Evaluation Guidelines

   No additional guidelines for expert review are anticipated.

13.3

11.3.  Signal TLV Type Registration

   A new repository must be created with the values of the DLEP signals.

   All signal values are in the range [0..255].

   Valid signals are:

   o  Peer Discovery

   o  Peer Offer

   o  Peer Initialization

   o  Peer Initialization ACK

   o  Peer Update

   o  Peer Update ACK

   o  Peer Termination

   o  Peer Termination ACK

   o  Destination Up

   o  Destination Up ACK

   o  Destination Down

   o  Destination Down ACK

   o  Destination Update

   o  Heartbeat

   o  Link Characteristics Request

   o  Link Characteristics ACK
   It is also requested that the repository contain space for
   experimental signal types.

13.4

11.4.  DLEP Data Item Registrations

   A new repository for DLEP Data Items data items must be created.

   All data item values are in the range [0..255].

   Valid Data
   Items data items are:

   o  DLEP Version

   o  Status

   o  DLEP Port

   o  Peer Type

   o  Heartbeat Interval

   o  Extensions Supported

   o  Experimental Definition

   o  MAC Address

   o  IPv4 Address

   o  IPv6 Address

   o  IPv4 Attached Subnet

   o  IPv6 Attached Subnet

   o  Maximum Data Rate (Receive)

   o  Maximum Data Rate (Transmit)

   o  Current Data Rate (Receive)

   o  Current Data Rate (Transmit)

   o  Latency

   o  Resources (Receive)

   o  Resources (Transmit)
   o  Relative Link Quality (Receive)

   o  Relative Link Quality (Transmit)

   o   Status
       o   Heartbeat Interval/Threshold
       o  Link Characteristics ACK Timer

   o  Credit Window Status

   o  Credit Grant

   o  Credit Request
       o

   It is also requested that the registry allocation contain space for
   experimental data items.

11.5.  DLEP Optional Signals Supported Status Code Registrations

   A new repository for DLEP status codes must be created.

   All status codes are in the range [0..255].

   Valid status codes are:

   o  Success (value 0)

   o  Unknown Signal

   o  Invalid Signal

   o  Unexpected Signal

   o  Request Denied

   o  Timed Out

11.6.  DLEP Optional Data Items Supported Extensions Registrations

   A new repository for DLEP extensions must be created.

   All extension values are in the range [0..255].

   Valid extensions are:

   o  DLEP_EXT_CREDITS - Credit windowing

11.7.  DLEP Vendor Extension Well-known Port

   It is requested that IANA allocate a well-known port number for DLEP
   communication.

11.8.  DLEP Multicast Address

   It is also requested that IANA allocate a multicast address for DLEP
   discovery signals.

12.  Acknowledgements

   The authors would like to acknowledge and thank the members of the
   DLEP design team, who have provided invaluable insight.  The members
   of the design team are: Teco Boot, Bow-Nan Cheng, John Dowdell, and
   Henning Rogge.

   The authors would also like to acknowledge the registry allocation contain space for
   experimental data items.

13.5  DLEP Well-known Port

   It is requested that IANA allocate a well-known port number influence and
   contributions of Greg Harrison, Chris Olsen, Martin Duke, Subir Das,
   Jaewon Kang, Vikram Kaul, and Nelson Powell.

13.  References

13.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for DLEP
   communication.

13.6  DLEP Multicast Address

   It is requested that IANA allocate a multicast address use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5578]  Berry, B., Ratliff, S., Paradise, E., Kaiser, T., and M.
              Adams, "PPP over Ethernet (PPPoE) Extensions for DLEP
   discovery signals.

14. Credit
              Flow and Link Metrics", RFC 5578, February 2010.

13.2.  Informative References

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

Appendix A.

14.1  Peer Level Signal Flows

14.1.1

   _NB_ The following diagrams are possibly out of date.  If there is a
   discepancy with the text, then the text is correct.

A.1.  Router Device Restarts Discovery
Router                       Modem    Signal Description
====================================================================

--------Peer Discovery-------->       Router initiates discovery

 <--------Peer Offer------------      Modem detects a problem, sends
   w/ Non-zero Status TLV             Peer Offer w/Status TLV indicating
                                      the error.

                                      Router accepts failure, restarts
                                      discovery process.

--------Peer Discovery-------->       Router initiates discovery

 <--------Peer Offer------------      Modem accepts, sends Peer Offer
                                      w/Zero Status TLV indicating
                                      success.

                                      Discovery completed.

14.1.2

A.2.  Router Device Detects Peer Offer Timeout

Router                       Modem    Signal Description
====================================================================

 --------Peer Discovery-------->      Router initiates discovery, starts
                                      a guard timer.

                                      Router guard timer expires. Router
                                      restarts discovery process.

 --------Peer Discovery-------->      Router initiates discovery, starts
                                      a guard timer.

 <--------Peer Offer------------      Modem accepts, sends Peer Offer
                                      w/Zero Status TLV indicating
                                      success.

                                      Discovery completed.

14.1.3

A.3.  Router Peer Offer Lost
 Router                       Modem    Signal Description
 ====================================================================

 <-------Peer Discovery---------       Modem initiates discovery, starts
                                       a guard timer.

  ---------Peer Offer-------||         Router offers availability

                                       Modem times out on Peer Offer,
                                       restarts discovery process.

 <-------Peer Discovery---------       Modem initiates discovery

  ---------Peer Offer----------->      Router detects subsequent
                                       discovery, internally terminates
                                       the previous, accepts the new
                                       association, sends Peer Offer
                                       w/Status TLV indicating success.

                                       Discovery completed.

14.1.4

A.4.  Discovery Success

 Router                       Modem    Signal Description
 ====================================================================

 <-------Peer Discovery---------       Modem initiates discovery

  ---------Peer Offer----------->      Router offers availability

 <-----Peer Initialization------       Modem Connects on TCP Port

 <------Peer Heartbeat----------

  -------Peer Heartbeat--------->

 <==============================>      Signal flow about destinations
                                       (i.e. Destination Up, Destination
                                       Down, Destination update)

 <-------Peer Heartbeat---------

  -------Peer Heartbeat--------->

  --------Peer Term Req--------->      Terminate Request

 <--------Peer Term Res---------       Terminate Response

14.1.5

A.5.  Router Detects a Heartbeat timeout

Router                       Modem    Signal Description
====================================================================

<-------Peer Heartbeat---------

 -------Peer Heartbeat--------->

   ||---Peer Heartbeat---------

       ~ ~ ~ ~ ~ ~ ~

 -------Peer Heartbeat--------->

  ||---Peer Heartbeat---------
                                      Router Heartbeat Timer expires,
                                      detects missing heartbeats. Router
                                      takes down all destination
                                      sessions and terminates the Peer
                                      association.

------Peer Terminate --------->       Peer Terminate Request

                                      Modem takes down all destination
                                      sessions, then acknowledges the
                                      Peer Terminate

<----Peer Terminate ACK---------      Peer Terminate ACK

14.1.6

A.6.  Modem Detects a Heartbeat timeout
 Router                       Modem    Signal Description
 ====================================================================

 <-------Peer Heartbeat---------

  -------Peer Heartbeat------||

 <-------Peer Heartbeat---------

        ~ ~ ~ ~ ~ ~ ~

  -------Peer Heartbeat------||

 <-------Peer Heartbeat---------
                                       Modem Heartbeat Timer expires,
                                       detects missing heartbeats. Modem
                                       takes down all destination
                                       sessions

 <-------Peer Terminate--------        Peer Terminate Request

                                       Router takes down all destination
                                       sessions, then acknowledges the
                                       Peer Terminate

 ------Peer Terminate ACK----->        Peer Terminate ACK

14.1.7

A.7.  Peer Terminate (from Modem) Lost

   Router                       Modem    Signal Description
   ====================================================================

    ||------Peer Terminate--------       Modem Peer Terminate Request

                                         Router Heartbeat times out,
                                         terminates association.

   --------Peer Terminate------->        Router Peer Terminate

   <-----Peer Terminate ACK------        Modem sends Peer Terminate ACK

14.1.8

A.8.  Peer Terminate (from Router) Lost
   Router                       Modem    Signal Description
   ====================================================================

   -------Peer Terminate-------->        Router Peer Terminate Request

                                         Modem HB times out,
                                         terminates association.

   <------Peer Terminate--------         Modem Peer Terminate

   ------Peer Terminate ACK----->        Peer Terminate ACK

14.2

Appendix B.  Destination Specific Signal Flows
14.2.1

B.1.  Modem Destination Up Lost

   Router                       Modem    Signal Description
   ====================================================================

    ||-----Destination Up ------------   Modem sends Destination Up

                                         Modem timesout on ACK

    <------Destination Up ------------   Modem sends Destination Up

    ------Destination Up ACK--------->   Router accepts the destination
                                         session

   <------Destination Update---------    Modem Destination Metrics
          . . . . . . . .
   <------Destination Update---------    Modem Destination Metrics

14.2.2

B.2.  Router Detects Duplicate Destination Ups
   Router                       Modem    Signal Description
   ====================================================================

   <------Destination Up ------------    Modem sends Destination Up

   ------Destination Up ACK-------||     Router accepts the destination
                                         session

                                         Modem timesout on ACK

   <------Destination Up ------------    Modem resends Destination Up

                                         Router detects duplicate
                                         Destination, takes down the
                                         previous, accepts the new
                                         Destination.

   ------Destination Up ACK--------->    Router accepts the destination
                                         session

   <------Destination Update---------    Modem Destination Metrics
          . . . . . . . .
   <------Destination Update---------    Modem Destination Metrics

14.2.3

B.3.  Destination Up, No Layer 3 Addresses

  Router                       Modem    Signal Description
  ====================================================================

  <------Destination Up ------------    Modem sends Destination Up

  ------Destination Up ACK--------->    Router accepts the destination
                                        session

                                        Router ARPs for IPv4 if defined.
                                        Router drives ND for IPv6 if
                                        defined.

  <------Destination Update---------    Modem Destination Metrics
         . . . . . . . .
  <------Destination Update---------    Modem Destination Metrics

14.2.4

B.4.  Destination Up with IPv4, No IPv6
   Router                       Modem    Signal Description
   ====================================================================

   <------Destination Up ------------    Modem sends Destination Up with
                                         the IPv4 TLV

   ------Destination Up ACK--------->    Router accepts the destination
                                         session

                                         Router drives ND for IPv6 if
                                         defined.

   <------Destination Update---------    Modem Destination Metrics
          . . . . . . . .
   <------Destination Update---------    Modem Destination Metrics

14.2.5

B.5.  Destination Up with IPv4 and IPv6

   Router                       Modem    Signal Description
   ====================================================================

   <------Destination Up ------------    Modem sends Destination Up with
                                         the IPv4 and IPv6 TLVs

   ------Destination Up ACK--------->    Router accepts the destination
                                         session

   <------Destination Update---------    Modem Destination Metrics
          . . . . . . . .

14.2.6

B.6.  Destination Session Success
   Router                       Modem    Signal Description
   ====================================================================

   ---------Peer Offer----------->       Router offers availability

   -------Peer Heartbeat--------->

   <------Destination Up -----------     Modem

   ------Destination Up ACK-------->     Router

   <------Destination Update---------    Modem
          . . . . . . . .
   <------Destination Update---------    Modem

                                         Modem initiates the terminate

   <------Destination Down ----------    Modem

   ------Destination Down ACK------->    Router

                                         or

                                         Router initiates the terminate

   ------Destination Down ---------->    Router

   <------Destination Down ACK-------    Modem

Acknowledgements

   The authors would like to acknowledge and thank the members of the
   DLEP design team, who have provided invaluable insight. The members
   of the design team are:  Teco Boot, Bow-Nan Cheng, John Dowdell,
   Henning Rogge, and Rick Taylor.

   The authors would also like to acknowledge the influence and
   contributions of Chris Olsen, Martin Duke, Subir Das, Jaewon Kang,
   Vikram Kaul, and Nelson Powell.

Normative References

   [RFC5578] Berry, B., Ed., "PPPoE with Credit Flow and Metrics",
             RFC 5578, February 2010.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate

   [IEEE]    http://standards.ieee.org/develop/regauth/oui/index.html

Informative References

   [TLS]  Dierks, T. and Rescorla, E. "The Transport Layer Security
          (TLS) Protocol", RFC 5246, August 2008.

Author's

Authors' Addresses

   Stan Ratliff
   Independent Consultant
   VT iDirect
   13861 Sunrise Valley Drive, Suite 300
   Herndon, VA  20171
   USA
   EMail: ratliffstan@gmail.com

   Email: sratliff@idirect.net

   Bo Berry
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   USA
   EMail:

   Greg Harrison
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   USA
   EMail: greharri@cisco.com
   Shawn Jury
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: sjury@cisco.com

   Darryl Satterwhite
   Broadcom
   USA

   Email: dsatterw@broadcom.com

   Rick Taylor
   Airbus Defence & Space
   Quadrant House
   Celtic Springs
   Coedkernew
   Newport  NP10 8FZ
   UK

   Email: rick.taylor@airbus.com