Mobile Ad hoc Networks Working Group                          S. Ratliff
Internet-Draft                                                VT iDirect
Intended status: Standards Track                                B. Berry
Expires: August 31, October 15, 2015
                                                                 S. Jury
                                                           Cisco Systems
                                                          D. Satterwhite
                                                                Broadcom
                                                               R. Taylor
                                                  Airbus Defence & Space
                                                       February 27,
                                                          April 13, 2015

                 Dynamic Link Exchange Protocol (DLEP)
                        draft-ietf-manet-dlep-08
                        draft-ietf-manet-dlep-09

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 Memo

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   This Internet-Draft will expire on August 31, October 15, 2015.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Protocol Overview . . . . . . . . . . . . . . . . . . . .   7
     1.2.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   8
   2.  Assumptions . . . . . . . . . . . . . . . . . . . . . . . . .   8
   3.  Core Features and Optional Extensions . . . . . . . . . . . .  10
     3.1.  Negotiation of Optional Extensions  . . . . . . . . . . .  10
     3.2.  Protocol Extensions . . . . . . . . . . . . . . . . . . .  10
     3.3.  Experimental Signals and Data Items . . . . . . . . . . .  11
   4.  Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  Mandatory Metrics . . . . . . . . . . . . . . . . . . . .  12
   5.  Normal Session Flow . . . . . . . . . . . . . . . . . . . . .  12
     5.1.
     4.2.  DLEP Router session flow - Discovery case . . . . . . . .  13
     5.2.  12
     4.3.  DLEP Router session flow - Configured case  . . . . . . .  13
     5.3.
     4.4.  DLEP Modem session flow . . . . . . . . . . . . . . . . .  14
     5.4.  13
     4.5.  Common Session Flow . . . . . . . . . . . . . . . . . . .  14
   6.
   5.  DLEP Message Processing . . . . . . . . . . . . . . . . . . .  15
     6.1.
     5.1.  DLEP Signal Header  . . . . . . . . . . . . . . . . . . .  16
     6.2.
     5.2.  DLEP Generic Data Item  . . . . . . . . . . . . . . . . .  16
   7.
   6.  DLEP Signals  . . . . . . . . . . . . . . . . . . . . . . . .  17
     7.1.
     6.1.  Peer Discovery Signal . . . . . . . . . . . . . . . . . .  17
     7.2.
     6.2.  Peer Offer Signal . . . . . . . . . . . . . . . . . . . .  18
     7.3.
     6.3.  Peer Initialization Signal  . . . . . . . . . . . . . . .  19
     7.4.  18
     6.4.  Peer Initialization ACK Signal  . . . . . . . . . . . . .  20
     7.5.  19
     6.5.  Peer Update Signal  . . . . . . . . . . . . . . . . . . .  21
     7.6.
     6.6.  Peer Update ACK Signal  . . . . . . . . . . . . . . . . .  22
     7.7.
     6.7.  Peer Termination Signal . . . . . . . . . . . . . . . . .  23
     7.8.
     6.8.  Peer Termination ACK Signal . . . . . . . . . . . . . . .  23
     7.9.  24
     6.9.  Destination Up Signal . . . . . . . . . . . . . . . . . .  24
     7.10.
     6.10. Destination Up ACK Signal . . . . . . . . . . . . . . . .  25
     7.11.
     6.11. Destination Down Signal . . . . . . . . . . . . . . . . .  26
     7.12.
     6.12. Destination Down ACK Signal . . . . . . . . . . . . . . .  26
     7.13.
     6.13. Destination Update Signal . . . . . . . . . . . . . . . .  26
     7.14.  27
     6.14. Heartbeat Signal  . . . . . . . . . . . . . . . . . . . .  28
     7.15.
     6.15. Link Characteristics Request Signal . . . . . . . . . . .  28
     7.16.
     6.16. Link Characteristics ACK Signal . . . . . . . . . . . . .  29
   8.
   7.  DLEP Data Items . . . . . . . . . . . . . . . . . . . . . . .  30
     8.1.
     7.1.  DLEP Version  . . . . . . . . . . . . . . . . . . . . . .  31
     8.2.
     7.2.  Status  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     8.3.  DLEP Port
     7.3.  IPv4 Connection Point . . . . . . . . . . . . . . . . . .  33
     7.4.  IPv6 Connection Point . . . . . . . .  33
     8.4. . . . . . . . . . .  34
     7.5.  Peer Type . . . . . . . . . . . . . . . . . . . . . . . .  33
     8.5.  35
     7.6.  Heartbeat Interval  . . . . . . . . . . . . . . . . . . .  34
     8.6.  35
     7.7.  Extensions Supported  . . . . . . . . . . . . . . . . . .  35
     8.7.  36
     7.8.  Experimental Definition . . . . . . . . . . . . . . . . .  35
     8.8.  36
     7.9.  MAC Address . . . . . . . . . . . . . . . . . . . . . . .  36
     8.9.  37
     7.10. IPv4 Address  . . . . . . . . . . . . . . . . . . . . . .  37
     8.10.  38
     7.11. IPv6 Address  . . . . . . . . . . . . . . . . . . . . . .  37
     8.11.  38
     7.12. IPv4 Attached Subnet  . . . . . . . . . . . . . . . . . .  38
     8.12.  39
     7.13. IPv6 Attached Subnet  . . . . . . . . . . . . . . . . . .  39
     8.13.  40
     7.14. Maximum Data Rate (Receive) . . . . . . . . . . . . . . .  39
     8.14.  40
     7.15. Maximum Data Rate (Transmit)  . . . . . . . . . . . . . .  40
     8.15.  41
     7.16. Current Data Rate (Receive) . . . . . . . . . . . . . . .  41
     8.16.  42
     7.17. Current Data Rate (Transmit)  . . . . . . . . . . . . . .  41
     8.17.  42
     7.18. Latency . . . . . . . . . . . . . . . . . . . . . . . . .  42
     8.18.  43
     7.19. Resources (Receive) . . . . . . . . . . . . . . . . . . .  43
     8.19.  44
     7.20. Resources (Transmit)  . . . . . . . . . . . . . . . . . .  43
     8.20.  45
     7.21. Relative Link Quality (Receive) . . . . . . . . . . . . .  44
     8.21.  45
     7.22. Relative Link Quality (Transmit)  . . . . . . . . . . . .  45
     8.22.  46
     7.23. Link Characteristics ACK Timer  . . . . . . . . . . . . .  45
   9.  46
   8.  Credit-Windowing  . . . . . . . . . . . . . . . . . . . . . .  46
     9.1.  47
     8.1.  Credit-Windowing Signals  . . . . . . . . . . . . . . . .  46
       9.1.1.  47
       8.1.1.  Destination Up Signal . . . . . . . . . . . . . . . .  46
       9.1.2.  48
       8.1.2.  Destination Up ACK Signal . . . . . . . . . . . . . .  47
       9.1.3.  48
       8.1.3.  Destination Update Signal . . . . . . . . . . . . . .  47
     9.2.  48
     8.2.  Credit-Windowing Data Items . . . . . . . . . . . . . . .  47
       9.2.1.  48
       8.2.1.  Credit Window Status Grant  . . . . . . . . . . . . . . . .  47
       9.2.2.  Credit Grant . . . .  49
       8.2.2.  Credit Window Status  . . . . . . . . . . . . . . . .  48
       9.2.3.  50
       8.2.3.  Credit Request  . . . . . . . . . . . . . . . . . . .  49
   10.  50
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  50
   11.  51
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  50
     11.1.  51
     10.1.  Registrations  . . . . . . . . . . . . . . . . . . . . .  50
     11.2.  51
     10.2.  Expert Review: Evaluation Guidelines . . . . . . . . . .  51
     11.3.  52
     10.3.  Signal Type Registration . . . . . . . . . . . . . . . .  51
     11.4.  52
     10.4.  DLEP Data Item Registrations . . . . . . . . . . . . . .  52
     11.5.  53
     10.5.  DLEP Status Code Registrations . . . . . . . . . . . . .  53
     11.6.  54
     10.6.  DLEP Extensions Registrations  . . . . . . . . . . . . .  53
     11.7.  54
     10.7.  DLEP Well-known Port . . . . . . . . . . . . . . . . . .  54
     11.8.  55
     10.8.  DLEP Multicast Address . . . . . . . . . . . . . . . . .  54
   12.  55
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  54
   13.  55
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  54
     13.1.  55
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  54
     13.2.  55
     12.2.  Informative References . . . . . . . . . . . . . . . . .  54  55
   Appendix A.  Peer Level Signal Flows  . . . . . . . . . . . . . .  54  55
     A.1.  Router Device Restarts  Discovery . . . . . . . . . . . .  54
     A.2.  Router Device Detects Peer Offer Timeout  . . . . . . . .  55
     A.3.  Router Peer Offer Lost . . . . . .  55
     A.2.  Session Initialization  . . . . . . . . . . .  55
     A.4.  Discovery Success . . . . . .  56
     A.3.  Session Initialization - Refused  . . . . . . . . . . . .  57
     A.4.  Router Changes IP Addresses . . . .  56
     A.5.  Router Detects a Heartbeat timeout . . . . . . . . . . .  57
     A.6.
     A.5.  Modem Detects a Heartbeat timeout . Changes Session-wide Metrics  . . . . . . . . . . .  57
     A.7.  Peer Terminate (from Modem) Lost
     A.6.  Router Terminates Session . . . . . . . . . . . .  58
     A.8.  Peer Terminate (from Router) Lost . . . .  58
     A.7.  Modem Terminates Session  . . . . . . . .  58
   Appendix B.  Destination Specific Signal Flows . . . . . . . .  58
     A.8.  Session Heartbeats  . . .  59
     B.1.  Modem Destination Up Lost . . . . . . . . . . . . . . . .  59
     B.2.
     A.9.  Router Detects Duplicate Destination Ups a Heartbeat timeout  . . . . . . . .  59
     B.3.  Destination Up, No Layer 3 Addresses . . .  60
     A.10. Modem Detects a Heartbeat timeout . . . . . . .  60
     B.4.  Destination Up with IPv4, No IPv6 . . . . .  61
   Appendix B.  Destination Specific Signal Flows  . . . . . . . . .  60
     B.5.  61
     B.1.  Common Destination Up with IPv4 and IPv6 Signaling  . . . . . . . . . . . . . .  61
     B.6.
     B.2.  Multicast Destination Session Success Signaling . . . . . . . . . . . . .  62
     B.3.  Link Characteristics Request  . . . . . .  61 . . . . . . . .  62
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  62  63

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., 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., 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 Dynamic 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) 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 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

1.1.  Protocol Overview

   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 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 or the modem device supports multiple connections to a router
   (via multiple logical or physical interfaces), or supports
   connections to multiple routers, a then separate DLEP session MUST
   sessions exist for each modem or connection.  This router/modem
   session provides a carrier for information exchange concerning
   'destinations' that are available via the modem device.  A
   '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 multicast traffic is supported in DLEP
   simply by treating the derived MAC address as any other '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. destination.
   The modem, once it is aware of the existence of this logical neighbor,
   destination, reports link characteristics just as it would for any
   other destination in the network.  The specific algorithms a modem
   would use to report derive metrics on multicast (or logical) destinations is
   outside the scope of this specification, and is left to specific
   implementations to decide.

1.1.

1.2.  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 initializing the discovery process, using the Peer
   Discovery signal (Section 7.1). 6.1).

   DLEP utilizes a session-oriented paradigm.  A router and modem form a
   session by completing the discovery and initialization 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 the MAC address for delivering data traffic is the
   MAC specified in the Destination Up signal (Section 7.9). 6.9).  No
   manipulation or or substitution is performed; the MAC address supplied
   in Destination Up is used as the OSI Layer 2 Destination MAC address.
   DLEP also assumes that MAC addresses MUST be unique within the
   context of 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'.

   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).
   Note that since a destination is a MAC address, the MAC could
   reference a logical destination, as in a derived multicast MAC
   address, as well as to a physical device.  As destinations are
   discovered, DLEP routers and modems build an information base on
   destinations accessible via the modem.  Changes in link
   characteristics are then reported as being 'modem-wide' (effecting
   ALL

   The DLEP signals concerning destinations accessed via the modem, reported via the Peer Update
   signal, Section 7.5) or reported for a specific neighbor (via the
   Destination Update signal, Section 7.13).

   The DLEP signals concerning destinations thus become 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 (i.e., (i.e.  MAC
   address, and OPTIONALLY, Layer 3 addresses), link characteristics
   (metrics), and OPTIONALLY, flow control information (credits).

   DLEP assumes that any signal 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.

   DLEP assumes that security on the session (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 [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.  Core Features and Optional Extensions

   DLEP has a core set of signals and data items that MUST be processed
   without error by an implementation in order to guarantee
   interoperability and therefore make the implementation DLEP
   compliant.  This document defines the core set of signals and data
   items, listing them as 'mandatory'.  It should be noted that some
   core signals and data items might not be used during the lifetime of
   a single DLEP session, but a compliant implementation MUST support
   them.

   While this document 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 all likelihood be necessary as more
   link types are utilized.  To support future extension of DLEP, this
   document describes an extension negotiation capability to be used
   during session initialization via the Extensions Supported data item,
   documented in Section 8.6 7.7 of this document.

   All extensions are considered OPTIONAL.  Only the DLEP functionality
   listed as 'mandatory' is required by implementation in order to be
   DLEP compliant.

   This specification defines one extension, Credit processing, windowing, exposed
   via the Extensions Supported mechanism that implementations MAY chose
   choose to implement, or to omit.

3.1.  Negotiation of Optional Extensions

   Optional extensions supported by an implementation MUST be declared
   to potential DLEP peers using the Extensions Supported data item
   (Section 8.6) 7.7) during the 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 the received initialization
   signal from its peer.

3.2.  Protocol Extensions

   If/when protocol extensions are required, they should be standardized
   either as an update to this document, or as an additional stand-alone
   specification.  The requests for IANA-controlled registries in this
   document contain sufficient reserved space, both in terms of DLEP
   signals and DLEP data items, to accomodate accommodate future extensions to the
   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 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 signals, data items items, or behaviors MUST be
   announced by inclusion of an Experimental Definition data item
   (Section 8.7) 7.8) with a value agreed upon (a-priori) between 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 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., 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', 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' (those that apply to all destinations accessed via
   the modem).  Metrics  Most 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 logical destination only.

   DLEP modem implementations MUST announce all supported metric items,
   and provide default values for those metrics, in the Peer
   Initialization ACK signal (Section 7.3). 6.4).  In order to introduce a new
   metric type, DLEP modem implementations MUST terminate the session
   with the router (via the Peer Terminate signal, Section 7.7), signal (Section 6.7)), 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 destination (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) etc.) for
   utilizing the dual-context metrics is out of scope and not addressed
   by this document.

4.1.  Mandatory Metrics

   As mentioned above, DLEP modem implementations MUST announce all
   supported metric items during session initialization.  However, an
   implementation MUST include the following list of metrics:

   o  Maximum Data Rate (Receive) (Section 8.13) 7.14)

   o  Maximum Data Rate (Transmit) (Section 8.14) 7.15)

   o  Current Data Rate (Receive) (Section 8.15) 7.16)

   o  Current Data Rate (Transmit) (Section 8.16) 7.17)

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

5.1. 7.18)

4.2.  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) 6.1) to the DLEP link-local multicast
   address and port (TBD).  The implementation then waits on receipt of
   a Peer Offer signal (Section 7.2), 6.2), which MUST MAY contain the unicast
   address and port for TCP-based communication with a DLEP modem. modem, via
   the IPv4 Connection Point data item (Section 7.3) or the IPv6
   Connection Point data item (Section 7.4).  The Peer Offer signal MAY
   contain multiple address/port combinations. IP Connection Point data items.  If more than one address/port combination IP
   Connection Point data items is in the Peer Offer, the DLEP
   router implementation SHOULD consider the list to be in priority
   sequence, with the 'most desired' address/port combination listed
   first.  However, router
   implementations MAY use their own heuristics to determine the best
   address/port combination.  If no IP Connection Point data items are
   included in the Peer Offer signal, the receiver MUST use the origin
   address of the signal as the IP address, and the DLEP well-known port
   number (Section 10.7) to establish the TCP connection.  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.

5.2.

4.3.  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 router implementation MUST issue a Peer Initialization signal
   (Section 7.3) 6.3) to the DLEP router.  The Peer Initialization signal
   MUST contain data items for ALL supported metrics from this modem,
   along with the default values of those metrics.  After sending the modem.  After sending the Peer
   Initialization, the modem router implementation MUST wait for receipt of a
   Peer Initialization ACK signal (Section 7.4) 6.4) from the router. modem.  Receipt
   of the Peer Initialization ACK signal containing a Status data item
   (Section 7.2) with value 'Success', indicates that the
   router modem has
   received and processed the Peer Initialization, and the session MUST
   transition to the 'in session' state.  At this point, signals
   regarding destinations in the network, and/or Peer Update signals
   (Section 7.5), 6.5), can flow on the DLEP session between modem and
   router. router,
   and Heartbeat signals can begin to flow, if Heartbeats are used.  The
   '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.

5.3.

4.4.  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) 6.1) on the UDP socket, it responds by issuing a Peer Offer
   signal (Section 7.2) 6.2) to the sender of the Peer Discovery signal.  The
   Peer Offer signal MUST MAY contain the unicast address and port of the
   listening TCP listen socket, as 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 wait for receipt of a Peer Initialization signal (Section 6.3),
   sent by the router.  Upon receipt and successful parsing of a Peer
   Initialization signal, the modem MUST respond with a Peer
   Initialization ACK signal (Section 7.3). 6.4).  The Peer Initialization ACK
   signal MUST contain metric data items for ALL supported metrics.  If
   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 ACK signal.

5.4.  Once the Peer
   Initialization signal (Section 6.3) and Peer Initialization ACK
   signal (Section 6.4) have been exchanged, the session is transitioned
   to the 'in session' state.  As in the router case, when the 'in
   session' state is reached, signals regarding destinations in the
   network, and/or Peer Update signals (Section 6.5), can flow on the
   DLEP session between modem and router, and Heartbeat signals can
   begin to flow, if Heartbeats are used.  The 'in session' state
   persists until the session is explicitly terminated (using Peer
   Termination), or it times out (based on timeout values).

4.5.  Common Session Flow

   In order to maintain the session between router and modem, periodic
   Heartbeat signals (Section 7.14) 6.14) MAY be exchanged.  These signals are
   intended to keep the session alive, and to verify bidirectional
   connectivity between the two participants.  If [Heartbeat
   signals]#(sig_heartbeat) are exchanged, they do not begin until the
   DLEP peer session has entered the 'in session' state.  Each DLEP peer
   is responsible for the creation of Heartbeat signals (Section 6.14).
   Receipt of any DLEP signal SHOULD reset the heartbeat interval timer
   (e.g., valid DLEP signals take the place of, and obviate the need
   for, Heartbeat signals).

   DLEP also provides a Peer Update signal (Section 7.5), 6.5), 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 (Section 7.9). 6.9).  Receipt of a Destination Up
   causes the router to allocate the necessary resources, creating an
   entry in the information base with the specifics (i.e., (i.e.  MAC Address,
   Latency, Data Rate, etc) etc.) of the neighbor. destination.  The loss of a
   destination is communicated via the Destination Down signal
   (Section 7.11), 6.11), and changes in status to the destination (e.g.,
   varying link quality, or addressing changes) are communicated via the
   Destination Update signal (Section 7.13). 6.13).  The information on a given neighbor
   destination will persist in the router's information base until (1) a
   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.

   Metrics can be expressed within the context of a specific neighbor destination
   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, at peer
   level, 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 destination 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 a
   signal allowing a router to request a different datarate, or latency,
   from the modem.  This signal is referred to as the Link
   Characteristics Request signal (Section 7.15), 6.15), 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.

6.

5.  DLEP Message Processing

   Communication between DLEP peers consists of a bidirectional stream
   of signals, each signal consisting of a signal header and 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 the signal header are described as being
   'contained in' the signal.

   All integer values in all TLV structures MUST be in network byte-
   order.

   There is no restriction on the order of data items following a
   signal, and the multiplicity of duplicate data items is defined by
   the definition of the signal declared by the type in 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) 6.7) with a Status data item
   (Section 8.2) 7.2) containing the most relevant status code, and then
   close the TCP connection:

6.1. connection.

5.1.  DLEP Signal Header

   The DLEP signal 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 Type   | Length                        | Data Items...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 3: DLEP Signal Header

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

   Length:  The length, expressed as a 16-bit unsigned integer, of all
      of the DLEP data items associated with this signal.  This length
      does not include the length of the header itself

   Data Items:  One

   The DLEP Signal Header is immediately followed bu one or more DLEP
   data items, encoded in TLVs, as defined in this document.

6.2.

5.2.  DLEP Generic Data Item

   All DLEP 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Data Item Type| Length        | Value...                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 4: DLEP Generic Data Item

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

   Length:  An  The length, expressed as an 8-bit length unsigned integer, of the
      value field of the data item.

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

7.

6.  DLEP Signals

   As mentioned above, all DLEP signals begin with the DLEP signal
   header structure.  Therefore, in the following descriptions of
   specific signals, this header structure is assumed, and will not be
   replicated.

   Following is the set of MANDATORY signals that must be recognized by
   a DLEP 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:

        +---------+-------------------------------+---------------+
        | Signal  | Description                   | Section       |
        +---------+-------------------------------+---------------+
        | TBD     | Peer Discovery                | Section 7.1 6.1   |
        | TBD     | Peer Offer                    | Section 7.2 6.2   |
        | TBD     | Peer Initialization           | Section 7.3 6.3   |
        | TBD     | Peer Initialization ACK       | Section 7.4 6.4   |
        | TBD     | Peer Update                   | Section 7.5 6.5   |
        | TBD     | Peer Update ACK               | Section 7.6 6.6   |
        | TBD     | Peer Termination              | Section 7.7 6.7   |
        | TBD     | Peer Termination ACK          | Section 7.8 6.8   |
        | TBD     | Destination Up                | Section 7.9 6.9   |
        | TBD     | Destination Up ACK            | Section 7.10 6.10  |
        | TBD     | Destination Down              | Section 7.11 6.11  |
        | TBD     | Destination Down ACK          | Section 7.12 6.12  |
        | TBD     | Destination Update            | Section 7.13 6.13  |
        | TBD     | Heartbeat                     | Section 7.14 6.14  |
        | TBD     | Link Characteristics Request  | Section 7.15 6.15  |
        | TBD     | Link Characteristics ACK      | Section 7.16 6.16  |
        +---------+-------------------------------+---------------+

7.1.

6.1.  Peer Discovery Signal

   A Peer Discovery signal SHOULD be sent by a router to discover DLEP
   routers
   modems in the network.  The Peer Offer signal (Section 7.2) 6.2) 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 a Peer Discovery signal, the Signal Type value in the
   signal header is set to DLEP_PEER_DISCOVERY (value TBD).

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

   o  DLEP Version (Section 8.1) 7.1)

   The Peer Discovery signal MAY contain the following data item:

   o  Heartbeat Interval  Peer Type (Section 8.5)

7.2. 7.5)

6.2.  Peer Offer Signal

   A Peer Offer signal MUST be sent by a DLEP modem in response to a
   valid Peer Discovery signal (Section 7.1).  Upon receipt, and processing,
   of a Peer Offer signal, the router responds by issuing a TCP connect
   to the address/port combination specified in the received Peer Offer. 6.1).

   The Peer Offer signal MUST be sent to the unicast address of the
   originator of the Peer Discovery. Discovery signal.

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

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

   o  DLEP Version (Section 8.1)

   o  Heartbeat Interval (Section 8.5) 7.1)

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

   o  Peer Type (Section 8.4)

   o  DLEP Port (Section 8.3) 7.5)

   The Peer Offer signal MAY contain one or more of any of the following
   data items, with different values:

   o  IPv4 Address Connection Point (Section 8.9), with Add/Drop indicator = 1 7.3)

   o  IPv6 Address (Section 8.10), with Add/Drop indicator = 1

   If the Peer Offer signal includes a DLEP Port data item, the port
   number specified MUST be used to establish the TCP session.  If the
   DLEP Port number is omitted, the receiver MUST use the DLEP well-
   known port number Connection Point (Section 11.7) to establish the TCP connection. 7.4)

   The IP Address Connection Point data items indicate the unicast address the
   receiver of Peer Offer MUST use when connecting the DLEP TCP session.
   If multiple IP Address Connection Point data items are present in the Peer
   Offer signal, implementations MAY use their own heuristics to select
   the address to connect to.  If no IP Address Connection Point data items are
   included in the Peer Offer signal, the receiver MUST use the origin
   address of the signal as the IP address address, and the DLEP well-known port
   number (Section 10.7) to establish the TCP connection.

7.3.

6.3.  Peer Initialization Signal

   A Peer Initialization signal MUST be sent by a router as the first
   signal of the DLEP TCP session.  It is sent by the router after a TCP
   connect to an address/port combination that was obtained either via
   receipt of a Peer Offer, or from a-priori configuration.

   If any optional extensions are supported by the implementation, they
   MUST be enumerated in the Extensions Supported data item.  If an
   Extensions Supported data item does NOT exist in a Peer
   Initialization signal, the receiver of the signal MUST conclude that
   there is NO support for extensions in the sender.

   If any experimental signals or data items are used by the
   implementation, they MUST be enumerated in one or more Experimental
   Definition data items.  If there are no Experimental Definition data
   items in a Peer Initialization signal, the receiver of the signal
   MUST 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 Peer Initialization signal MUST contain one of each of the
   following data items:

   o  DLEP Version (Section 8.1) 7.1)

   o  Heartbeat Interval (Section 8.5) 7.6)

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

   o  Peer Type (Section 8.4) 7.5)

   o  Extensions Supported (Section 8.6) 7.7)

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

   o  Experimental Definition (Section 8.7)

7.4. 7.8)

   A Peer Initialization signal MUST be acknowledged by the receiver
   issuing a Peer Initialization ACK signal (Section 6.4).

6.4.  Peer Initialization ACK Signal

   A Peer Initialization ACK signal MUST be sent in response to a
   received Peer Initialization signal (Section 7.3). 6.3).  The Peer
   Initialization ACK signal completes the TCP-level DLEP session establishment;
   the sender of the signal should transition to an 'in- session' state
   when the signal is sent, and the receiver should transition to the
   'in-session' state upon receipt (and successful parsing) of a an
   acceptable Peer Initialization ACK signal.

   All supported metric 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 the modem 'declaring' all
   supported metrics at DLEP session initialization.  Receipt of any
   DLEP signal containing a metric data item NOT included in the Peer
   Initialization ACK signal MUST be treated as an error, resulting in
   the termination of the DLEP session between router and modem.

   If any optional extensions are supported by the modem, they MUST be
   enumerated in the Extensions Supported data item.  If an Extensions
   Supported data item does NOT exist in a Peer Initialization ACK
   signal, the receiver of the signal MUST conclude that there is NO
   support for extensions in the sender.

   If any experimental signals or data items are used by the
   implementation, they MUST be enumerated in one or more Experimental
   Definition data items.  If there are no Experimental Definition data
   items in a Peer Initialization ACK signal, the receiver of the signal
   MUST 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 to DLEP_PEER_INIT_ACK (value TBD).

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

   o  DLEP Version (Section 8.1) 7.1)

   o  Heartbeat Interval (Section 8.5) 7.6)

   o  Maximum Data Rate (Receive) (Section 8.13) 7.14)

   o  Maximum Data Rate (Transmit) (Section 8.14) 7.15)

   o  Current Data Rate (Receive) (Section 8.15) 7.16)

   o  Current Data Rate (Transmit) (Section 8.16) 7.17)

   o  Latency (Section 8.17) 7.18)
   The Peer Initialization ACK signal MAY MUST contain one of each of the
   following data items:

   o  Status (Section 8.2)

   o  Peer Type (Section 8.4) items, if the data item will be used during the
   lifetime of the session:

   o  Resources (Receive) (Section 8.18) 7.19)

   o  Resources (Transmit) (Section 8.19) 7.20)

   o  Relative Link Quality (Receive) (Section 8.20) 7.21)

   o  Relative Link Quality (Transmit) (Section 8.21)

   o  Extensions Supported 7.22)

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

   o  Status (Section 7.2)

   o  Peer Type (Section 7.5)

   o  Extensions Supported (Section 8.6) 7.7)

   The Peer Initialization ACK signal MAY contain one or more of any of
   the following data items, with different values:

   o  Experimental Definition (Section 8.7)

7.5. 7.8)

6.5.  Peer Update Signal

   A Peer Update signal MAY be 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 MAY prompt a
   Peer Update signal to its attached DLEP modems.  Also, for example, a
   modem that changes its Maximum Data Rate (Receive) 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), the address update would prompt any remote DLEP modems
   (DLEP-enabled modems in a remote node) to issue a Destination Update
   signal (Section 7.13) 6.13) to their local routers with the new (or
   deleted) addresses.  Modems that do not track Layer 3 addresses
   SHOULD silently parse and ignore the Peer Update signal.  Modems that
   track Layer 3 addresses MUST acknowledge the Peer Update with a Peer
   Update ACK signal (Section 7.6).  Routers receiving a 6.6).

   If metrics are supplied with the Peer Update
   with metric changes signal (e.g., Maximum
   Data Rate), these metrics are considered to be modem-wide, and
   therefore MUST apply the new metric be applied to all destinations
   (remote nodes) accessible via in the modem. information base
   associated with the router/modem session.

   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 that the other implementation does NOT
   support Layer 3 address tracking.

   If metrics are supplied with the Peer Update signal (e.g., Maximum
   Data Rate), these metrics are considered to be modem-wide, and
   therefore MUST be applied to all destinations in the information base
   associated with the router/modem session.

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

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

   o  Maximum Data Rate (Receive) (Section 8.13) 7.14)

   o  Maximum Data Rate (Transmit) (Section 8.14) 7.15)

   o  Current Data Rate (Receive) (Section 8.15) 7.16)

   o  Current Data Rate (Transmit) (Section 8.16) 7.17)

   o  Latency (Section 8.17) 7.18)

   o  Resources (Receive) (Section 8.18) 7.19)

   o  Resources (Transmit) (Section 8.19) 7.20)

   o  Relative Link Quality (Receive) (Section 8.20) 7.21)

   o  Relative Link Quality (Transmit) (Section 8.21) 7.22)

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

   o  IPv4 Address (Section 8.9) 7.10)

   o  IPv6 Address (Section 8.10)

7.6. 7.11)

   A Peer Update signal MUST be acknowledged by the receiver issuing a
   Peer Update ACK signal (Section 6.6).

6.6.  Peer Update ACK Signal

   A Peer Update ACK 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) 6.5) was successfully
   processed.  If the Peer Update ACK is issued, it MUST contain a
   Status data item, indicating the success or failure of processing the
   received Peer Update. received.

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

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

   o  Status (Section 8.2) 7.2)

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

7.7.

6.7.  Peer Termination Signal

   A Peer Termination signal MUST be sent by a DLEP participant when the
   router/modem session needs to be terminated.  Implementations
   receiving a Peer Termination signal MUST send a Peer Termination ACK
   signal (Section 7.8) 6.8) to confirm the termination process.

   The sender
   of a Peer Termination signal is free to define its heuristics in
   event of a timeout.  The receiver of a Peer Termination signal MUST release all resources
   allocated for the 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 the 'discovery' state.  No Destination Down signals
   (Section 7.11) 6.11) are sent.

   The sender of a Peer Termination signal is free to define its
   heuristics in event of a timeout.  It may resend the Peer Termination
   or free resources and return to the 'discovery' state.

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

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

   o  Status (Section 8.2) 7.2)

   A receiver of a Peer Termination signal without a Status data item
   MUST behave as if a Status data item with status code 'Success' 'Success',
   implying graceful termination, had been received.

7.8.

   A Peer Termination signal MUST be acknowledged by the receiver
   issuing a Peer Termination ACK signal (Section 6.8).

6.8.  Peer Termination ACK Signal

   A Peer Termination ACK signal MUST be sent by a DLEP peer in response
   to a received Peer Termination signal (Section 7.7). 6.7).  Receipt of a
   Peer Termination ACK signal completes the teardown of the router/
   modem session.

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

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

   o  Status (Section 8.2) 7.2)

   A receiver of a Peer Termination ACK signal without a Status data
   item MUST behave as if a Status data item with status code 'Success' 'Success',
   implying graceful termination, had been received.

7.9.

6.9.  Destination Up Signal

   A DLEP 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 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.

   A Destination Up signal MUST be acknowledged by the receiver issuing
   a Destination Up ACK signal (Section 6.10).  The sender of the
   Destination Up signal is free to define its retry heuristics in event
   of a timeout.  When a Destination Up signal is received and
   successfully processed, the receiver should add knowledge of the new
   destination to its information base, indicating that the 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 DLEP_DESTINATION_UP (value TBD).

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

   o  MAC Address (Section 8.8) 7.9)

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

   o  Maximum Data Rate (Receive) (Section 8.13) 7.14)

   o  Maximum Data Rate (Transmit) (Section 8.14) 7.15)
   o  Current Data Rate (Receive) (Section 8.15) 7.16)

   o  Current Data Rate (Transmit) (Section 8.16) 7.17)

   o  Latency (Section 8.17) 7.18)

   o  Resources (Receive) (Section 8.18) 7.19)

   o  Resources (Transmit) (Section 8.19) 7.20)

   o  Relative Link Quality (Receive) (Section 8.20) 7.21)

   o  Relative Link Quality (Transmit) (Section 8.21) 7.22)

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

   o  IPv4 Address (Section 8.9) 7.10)

   o  IPv6 Address (Section 8.10) 7.11)

   o  IPv4 Attached Subnet (Section 8.11) 7.12)

   o  IPv6 Attached Subnet (Section 8.12) 7.13)

   If the sender has IPv4 and/or IPv6 address information for a
   destination it SHOULD include the relevant data items in the
   Destination Up signal, reducing the need for the receiver to probe
   for any address.

7.10.

6.10.  Destination Up ACK Signal

   A DLEP participant MUST send a Destination Up ACK signal to indicate
   whether a Destination Up signal (Section 7.9) 6.9) was successfully
   processed.

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

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

   o  MAC Address (Section 8.8) 7.9)

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

   o  Status (Section 8.2) 7.2)
   A receiver of a Destination Up ACK signal without a Status data item
   MUST behave as if a Status data item with status code 'Success' had
   been received.

7.11.

6.11.  Destination Down Signal

   A DLEP 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) 6.12) MUST be sent
   by the recipient of a Destination Down signal to confirm that the
   relevant data has been removed from the information base.  The sender
   of the 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. 7.9)

6.12.  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) 6.11)
   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) 7.9)

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

   o  Status (Section 8.2) 7.2)

   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.

6.13.  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 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) 7.9)

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

   o  Maximum Data Rate (Receive) (Section 8.13) 7.14)

   o  Maximum Data Rate (Transmit) (Section 8.14) 7.15)

   o  Current Data Rate (Receive) (Section 8.15) 7.16)

   o  Current Data Rate (Transmit) (Section 8.16) 7.17)

   o  Latency (Section 8.17) 7.18)

   o  Resources (Receive) (Section 8.18) 7.19)

   o  Resources (Transmit) (Section 8.19) 7.20)

   o  Relative Link Quality (Receive) (Section 8.20) 7.21)

   o  Relative Link Quality (Transmit) (Section 8.21) 7.22)

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

   o  IPv4 Address (Section 8.9) 7.10)

   o  IPv6 Address (Section 8.10) 7.11)

   o  IPv4 Attached Subnet (Section 8.11) 7.12)
   o  IPv6 Attached Subnet (Section 8.12)

7.14. 7.13)

6.14.  Heartbeat Signal

   A Heartbeat signal SHOULD be sent by a DLEP participant every N
   seconds, where N is defined in the Heartbeat Interval field data item of
   the Peer Initialization signal (Section 7.3) 6.3) or Peer Initialization
   ACK signal (Section 7.4). 6.4).  Note that implementations setting the
   Heartbeat Interval to 0 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.

6.15.  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 destination
   (e.g., a remote node), or a logical destination (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) 6.16) 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 NOT assume that the request failed. succeeded.
   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) 7.9)

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

   o  Link Characteristics ACK Timer (Section 8.22) 7.23)

   o  Current Data Rate (Receive) (Section 8.15) 7.16)

   o  Current Data Rate (Transmit) (Section 8.16) 7.17)

   o  Latency (Section 8.17)

7.16. 7.18)

6.16.  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) 6.15) was successfully processed.  The Link Characteristics
   ACK signal SHOULD contain a complete set of metric data items. items, and
   MUST contain a full set (i.e. those declared in the Peer
   Initialization ACK signal (Section 6.4)), if metrics were requested
   by only including a MAC address data item.  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) 7.9)

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

   o  Maximum Data Rate (Receive) (Section 7.14)

   o  Maximum Data Rate (Transmit) (Section 7.15)
   o  Current Data Rate (Receive) (Section 8.15) 7.16)

   o  Current Data Rate (Transmit) (Section 8.16) 7.17)

   o  Latency (Section 8.17) 7.18)

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

   o  Resources (Receive) (Section 8.18) 7.19)

   o  Resources (Transmit) (Section 8.19) 7.20)

   o  Relative Link Quality (Receive) (Section 8.20) 7.21)

   o  Relative Link Quality (Transmit) (Section 8.21) 7.22)

   o  Status (Section 8.2) 7.2)

   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.

7.  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 7.1   |
   | TBD        | Status                               | Section 8.2 7.2   |
   | TBD        | DLEP Port IPv4 Connection Point                | Section 7.3   |
   | TBD        | IPv6 Connection Point                | Section 8.3 7.4   |
   | TBD        | Peer Type                            | Section 8.4 7.5   |
   | TBD        | Heartbeat Interval                   | Section 8.5 7.6   |
   | TBD        | Extensions Supported                 | Section 8.6 7.7   |
   | TBD        | Experimental Definition              | Section 8.7 7.8   |
   | TBD        | MAC Address                          | Section 8.8 7.9   |
   | TBD        | IPv4 Address                         | Section 8.9 7.10  |
   | TBD        | IPv6 Address                         | Section 8.10 7.11  |
   | TBD        | IPv4 Attached Subnet                 | Section 8.11 7.12  |
   | TBD        | IPv6 Attached Subnet                 | Section 8.12 7.13  |
   | TBD        | Maximum Data Rate (Receive) MDRR)    | Section 8.13 7.14  |
   | TBD        | Maximum Data Rate (Transmit) (MDRT)  | Section 8.14 7.15  |
   | TBD        | Current Data Rate (Receive) (CDRR)   | Section 8.15 7.16  |
   | TBD        | Current Data Rate (Transmit) (CDRT)  | Section 8.16 7.17  |
   | TBD        | Latency                              | Section 8.17 7.18  |
   | TBD        | Resources (Receive) (RESR)           | Section 8.18 7.19  |
   | TBD        | Resources (Transmit) (REST)          | Section 8.19 7.20  |
   | TBD        | Relative Link Quality (Receive)      | Section 8.20 7.21  |
   |            | (RLQR)                               |               |
   | TBD        | Relative Link Quality (Transmit)     | Section 8.21 7.22  |
   |            | (RLQT)                               |               |
   | TBD        | Link Characteristics ACK Timer       | Section 8.22 7.23  |
   +------------+--------------------------------------+---------------+

8.1.

7.1.  DLEP Version

   The DLEP Version data item MUST appear in the Peer Discovery
   (Section 7.1), 6.1), Peer Offer (Section 7.2), 6.2), Peer Initialization
   (Section 7.3) 6.3) and Peer Initialization ACK (Section 7.4) 6.4) signals The
   Version data item is used to indicate the version of the protocol
   running in the originator.  A DLEP implementation MAY SHOULD use this
   information to decide if the potential session partner is running at
   a supported level.

   The 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type|    Length = 4     |         Major Version         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Minor Version           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  4

   Major Version:  Major  The major version of the DLEP protocol. protocol, expressed as
      an 16-bit unsigned integer.

   Minor Version:  Minor  The minor version of the DLEP protocol. protocol, expressed as
      an 16-bit unsigned integer.

   Support of this draft is indicated by setting the Major Version to
   '0', and the Minor Version to '8' (i.e., '9' (i.e.  Version 0.8).

8.2. 0.9).

7.2.  Status

   The Status data item is MAY appear in the Peer Initialization ACK
   (Section 7.4), 6.4), Peer Termination (Section 7.7), 6.7), Peer Termination ACK
   (Section 7.8), 6.8), Peer Update ACK (Section 7.6), 6.6), Destination Up ACK
   (Section 7.10), 6.10), Destination Down ACK (Section 7.12) 6.12) and Link
   Characteristics ACK (Section 7.16) 6.16) 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 status data item contains includes an optional Text field that can be used
   to provide a textual description 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | status.  The use of the Text
   field is entirely up to the receiving implementation, i.e., it could
   be output to a log file or discarded.  If no Text field is supplied
   with the Status data item, the Length field MUST be set to 1.

   The 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 = 1     |     Code      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Text...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1 + Length of text
   Status Code:  One of the codes defined below.

   +-------------------+-----------------------------------------------+

   Text:  UTF-8 encoded string, describing an problem, used for
      implementation defined purposes.

   An implementation MUST NOT assume the Text field is NUL-terminated.

   +----------------+-------+------------------------------------------+
   | Status Code    | Value | Reason                                   |
   +-------------------+-----------------------------------------------+
   +----------------+-------+------------------------------------------+
   | Success        | 0     | The signal was processed successfully.   |
   | Unknown Signal | TBD   | The signal was not recognized by the     |
   |                |       | implementation.                          |
   | Invalid Signal Data   | TBD   | One or more data items in the signal are |
   |                |       | invalid, unexpected or duplicated.       |
   | Unexpected Signal     | TBD   | The signal was not expected while the machine    |
   | Signal         |       | machine was in this state, e.g., a Peer  |
   |                |       | Initialization signal after session      |
   |                |       | establishment.                           |
   | Request Denied | TBD   | The receiver has not completed the       |
   |                |       | request.                                 |
   | Timed Out      | TBD   | The request could not be completed in the    |
   |                |       | the time allowed.                        |
   +-------------------+-----------------------------------------------+

8.3.  DLEP Port
   | Invalid        | TBD   | The DLEP Port destination provided in the signal   |
   | Destination    |       | does not match a previously announced    |
   |                |       | destination. For example, in the Link    |
   |                |       | Characteristic Request ACK signal        |
   |                |       | (Section 6.16).                          |
   +----------------+-------+------------------------------------------+

7.3.  IPv4 Connection Point

   The IPv4 Connection Point data item MAY appear in the Peer Offer
   signal (Section 7.2). 6.2).  The DLEP Port IPv4 Connection Point data item indicates
   the IPv4 address and, optionally, the TCP Port port number on the DLEP server
   modem available for connections.  If provided, the receiver MUST use
   this information to perform the TCP connect to the DLEP server.

   The DLEP Port IPv4 Connection Point 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 = 2     |          IPv4 Address         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          IPv4 Address         |   TCP Port Number (optional)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Data Item Type:  TBD

   Length:  2  4 (or 6 if TCP Port included)

   IPv4 Address:  The IPv4 address listening on the DLEP modem.

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

8.4.  Peer Type

   The Peer Type data item MAY appear in both modem.

   If the Peer Discovery
   (Section 7.1) and Peer Offer (Section 7.2) signals.  The Peer Type
   data item Length field is used by 6, the router and modem to give additional
   information as port number specified MUST be used to its type.  The peer type
   establish the TCP session.  If the TCP Port Number is a string and omitted, i.e.
   the Length field is
   envisioned 4, the receiver MUST use the DLEP well-known port
   number (Section 10.7) to be used for informational purposes (e.g., as output in
   a display command). establish the TCP connection.

7.4.  IPv6 Connection Point

   The IPv6 Connection Point data item MAY appear in the Peer Type Offer
   signal (Section 6.2).  The IPv6 Connection Point data item indicates
   the IPv6 address and, optionally, the TCP port number on the DLEP
   modem available for connections.  If provided, the receiver MUST use
   this information to perform the TCP connect to the DLEP server.

   The IPv4 Connection Point 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 = peer     | Peer Type          IPv6 Address         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    type len                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          IPv6 Address         |   TCP Port Number (optional)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  16 (or 18 if TCP Port included)

   IPv6 Address:  The IPv6 address listening on the DLEP modem.

   TCP Port Number:  TCP Port number on the DLEP modem.

   If the Length of peer type string.

   Peer Type:  UTF-8 encoded string.  For example, a satellite modem
      might set this variable field is 18, the port number specified MUST be used to "Satellite terminal".

   An implementation
   establish the TCP session.  If the TCP Port Number is omitted, i.e.

   the Length field is 16, the receiver MUST NOT assume use the DLEP well-known
   port number (Section 10.7) to establish the TCP connection.

7.5.  Peer Type is NUL-terminated.

8.5.  Heartbeat Interval

   The Heartbeat Interval Peer Type data item MUST MAY appear in the Peer Discovery
   (Section 7.1), 6.1), Peer Offer (Section 7.2), 6.2), Peer Initialization
   (Section 7.3) 6.3) and Peer Initialization ACK (Section 7.4) signals to
   indicate the desired Heartbeat timeout window. 6.4) signals.  The receiver MUST
   either accept the timeout interval supplied
   Peer Type data item is used by the sender, or reject 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 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type|    Length     | Peer Initialization, and close Type                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  Length of peer type string.

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

   An implementation MUST NOT assume the socket.  Implementations Peer Type field is NUL-
   terminated.

7.6.  Heartbeat Interval

   The Heartbeat Interval data item MUST
   implement heuristics such that DLEP appear in both the Peer
   Initialization (Section 6.3) and Peer Initialization ACK
   (Section 6.4) signals sent/received reset to indicate the
   timer interval. Heartbeat timeout window to be
   used by the sender.

   The Interval is used to specify a period (in seconds) for Heartbeat
   signals (Section 7.14). 6.14).  By specifying an Interval value of 0,
   implementations MAY indicates the desire to disable Heartbeat signals
   entirely (i.e., the Interval is set to an infinite value), however, value).  However,
   it is strongly recommended that implementations use non 0 timer
   values.  Implementations MUST implement heuristics such that DLEP
   signals sent/received reset the timer interval.

   A DLEP session will be considered inactive, and MUST be torn down,
   via the Peer Termination procedure, by an implementation detecting
   that two (2) Heartbeat intervals have transpired without receipt of
   any DLEP signals.

   The 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type|    Length = 2     |           Interval            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  2

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

8.6.

7.7.  Extensions Supported

   The Extensions Supported data item MAY be used in both the Peer
   Initialization and Peer Initialization ACK signals.  The Extensions
   Supported data item is used by the router and modem to negotiate
   additional optional functionality they are willing to support.  The
   Extensions List is a concatenation of the types of each supported
   extension, found in the IANA DLEP 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type|    Length = No.     | Extensions List               |
   |               |   of values   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  Number of Extensions supported.

   Extension List:  A list of extensions supported, identified by their
      1-octet value as listed in the extensions registry.

8.7.

7.8.  Experimental Definition

   The Experimental Definition data item MAY be used in both the Peer
   Initialization and Peer Initialization ACK signals.  The Experimental
   Definition data item is used by the router and modem to indicate the
   formats to be used for experimental signals and data items for the
   given peer session.  The formats are identified by using a string
   that matches the 'name' given to the experiment.

   The Experimental Definition 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 = len.     | Experiment Name               |
   |               | of Experiment |                               |
   |               |      name     |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  Length of the name string for the Experiment.

   Experiment Name:  UTF-8 encoded string, containing the name of the
      experiment being utilized.

   An implementation receiving this data item MUST compare the received
   string to a list of experiments that it supports.

   An implementation MUST NOT assume the Experiment Name field is NUL-terminated.

8.8. NUL-
   terminated.

7.9.  MAC Address

   The MAC address data item MUST appear in all destination-oriented
   signals (i.e., Destination Up (Section 7.9), 6.9), Destination Up ACK
   (Section 7.10), 6.10), Destination Down (Section 7.11), 6.11), Destination Down ACK
   (Section 7.12), 6.12), Destination Update (Section 7.13), 6.13), Link
   Characteristics Request (Section 7.15), 6.15), and Link Characteristics ACK
   (Section 7.16)). 6.16)).  The MAC Address data item contains the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type|    Length = 6     |          MAC Address          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      MAC Address                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  6
   MAC Address:  MAC Address of the destination (either physical or
      virtual).

8.9. destination.

7.10.  IPv4 Address

   The IPv4 Address data item MUST appear in the Peer Offer signal
   (Section 7.2), and MAY appear in the Peer Update
   (Section 7.5), 6.5), Destination Up (Section 7.9) 6.9) and Destination Update
   (Section 7.13) 6.13) signals.  When included in Destination signals, this
   data item contains the IPv4 address of the destination.  In  When
   included in the Peer Offer Update signal, it this data item contains the IPv4
   address of the originating peer to be
   used to establish a DLEP session. peer.  In either case, the data item also contains an
   indication of whether this is a new or existing address, or is a
   deletion of a previously known address.  When used in a Peer
   Offer signal 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type|    Length = 5     |   Add/Drop    | IPv4 Address  |
   |               |               |   Indicator   |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            IPv4 Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  5

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

   IPv4 Address:  The IPv4 address of the destination or peer.

8.10.

7.11.  IPv6 Address

   The IPv6 Address data item MUST appear in the Peer Offer signal
   (Section 7.2), and MAY appear in the Peer Update
   (Section 7.5), 6.5), Destination Up (Section 7.9) 6.9) and Destination Update
   (Section 7.13) 6.13) signals.  When included in Destination signals, this
   data item contains the IPv6 address of the destination.  In  When
   included in the Peer Offer Update signal, it this data item contains the IPv6 IPv4
   address of the originating peer to be
   used to establish a DLEP session. peer.  In either case, the data item also contains an
   indication of whether this is a new or existing address, or is a
   deletion of a previously known address.  When used in a Peer
   Offer signal the Add/Drop Indicator MUST be 1 (i.e.  Add).

   The IPv6 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type|    Length = 17     |   Add/Drop    | IPv6 Address  |
   |               |               |   Indicator   |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv6 Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                IPv6 Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  17

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

   IPv6 Address:  IPv6 Address of the destination or peer.

8.11.

7.12.  IPv4 Attached Subnet

   The DLEP IPv4 Attached Subnet allows a device to declare that it has
   an IPv4 subnet (e.g., a stub network) attached. attached, and MAY appear in the
   Destination Up (Section 6.9) and Destination Update (Section 6.13)
   signals.  Once an IPv4 Subnet has been declared on a device, the
   declaration can NOT be withdrawn without terminating the destination
   (via the Destination Down signal) signal (Section 6.11)) and re-issuing the
   Destination Up signal.

   The DLEP 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 Type |    Length = 5     | IPv4 Attached Subnet          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv4 Attached Subnet     | Subnet Mask   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  5
   IPv4 Subnet:  The IPv4 subnet reachable at the destination.

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

8.12.

7.13.  IPv6 Attached Subnet

   The DLEP IPv6 Attached Subnet allows a device to declare that it has
   an IPv6 subnet (e.g., a stub network) attached. attached, and MAY appear in the
   Destination Up (Section 6.9) and Destination Update (Section 6.13)
   signals.  As in the case of the IPv4 attached Subnet data item above,
   once an IPv6 attached subnet has been declared, it can NOT be
   withdrawn without terminating the destination (via the Destination Down)
   Down signal (Section 6.11)) and re-issuing the Destination Up signal.

   The DLEP IPv6 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 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 the destination.

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

8.13.

7.14.  Maximum Data Rate (Receive)

   The Maximum Data Rate (Receive) (MDRR) data item MUST appear in the
   Peer Initialization ACK signal (Section 7.4), 6.4), and MAY appear in the
   Peer Update (Section 7.5), 6.5), Destination Up (Section 7.9) and 6.9), Destination
   Update (Section 7.13) 6.13) and Link Characteristics ACK (Section 6.16)
   signals to indicate the maximum theoretical data rate, in bits per
   second, that can be achieved while receiving data on the link.

   The Maximum 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     |          MDRR (bps)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        MDRR (bps)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           MDRR (bps)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  8

   Maximum Data Rate (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.

7.15.  Maximum Data Rate (Transmit)

   The Maximum Data Rate (Transmit) (MDRT) data item MUST appear in the
   Peer Initialization ACK signal (Section 7.4), 6.4), and MAY appear in the
   Peer Update (Section 7.5), 6.5), Destination Up (Section 7.9) and 6.9), Destination
   Update (Section 7.13) 6.13) and Link Characteristics ACK (Section 6.16)
   signals to indicate the maximum theoretical data rate, in bits per
   second, that 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 (Transmit):  A 64-bit unsigned integer,
      representing the maximum theoretical data rate, in bits per second
      (bps), that can be achieved while transmitting on the link.

8.15.

7.16.  Current Data Rate (Receive)

   The Current Data Rate (Receive) (CDRR) data item MUST appear in the
   Peer Initialization ACK signal (Section 7.4), 6.4), and MAY appear in the
   Peer Update (Section 7.5), 6.5), Destination Up (Section 7.9), 6.9), Destination
   Update (Section 7.13), Link Characteristics Request (Section 7.15) 6.13) and Link Characteristics ACK (Section 7.16) 6.16)
   signals to indicate the rate at which the link is currently operating
   for receiving traffic.

   When used in the Link Characteristics Request signal, signal (Section 6.15),
   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 current data rate, in bits per second, that is can currently be
      achieved while receiving traffic on the link.

   If there is no distinction between current and maximum receive data
   rates, current data rate receive MUST be set equal to the maximum
   data rate receive.

8.16.

7.17.  Current Data Rate (Transmit)

   The Current Data Rate Receive Transmit (CDRT) data item MUST appear in the
   Peer Initialization ACK signal (Section 7.4), 6.4), and MAY appear in the
   Peer Update (Section 7.5), 6.5), Destination Up (Section 7.9), 6.9), Destination
   Update (Section 7.13), Link Characteristics Request (Section 7.15) 6.13), and Link Characteristics ACK (Section 7.16) 6.16)
   signals to indicate the rate at which the link is currently operating
   for transmitting traffic.

   When used in the Link Characteristics Request signal, signal (Section 6.15),
   CDRT represents the desired transmit rate, in bits per second, on the
   link.

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

   Data Item Type:  TBD

   Length:  8

   Current Data Rate (Transmit):  A 64-bit unsigned integer,
      representing the current data rate, in bits per second, that is can
      currently be achieved while transmitting traffic on the link.

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

8.17.

7.18.  Latency

   The Latency data item data item MUST appear in the Peer
   Initialization ACK signal (Section 7.4), 6.4), and MAY appear in the Peer
   Update (Section 7.5), 6.5), Destination Up (Section 7.9), 6.9), Destination
   Update (Section 7.13), Link Characteristics Request (Section 7.15) 6.13), and Link Characteristics ACK (Section 7.16) 6.16)
   signals to indicate the amount of latency, in microseconds, on the link, or
   link.

   When used in the case of
   the Link Characteristics Request, to indicate Request signal (Section 6.15),
   Latency represents the maximum latency
   required desired on the link.

   The Latency value is reported as delay.  The calculation of latency
   is 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 Type|    Length = 4     | Latency in microseconds                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Latency (cont.) microsecs              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  4

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

8.18.

7.19.  Resources (Receive)

   The Resources (Receive) (RESR) data item MAY appear in the Peer
   Initialization ACK signal (Section 7.4), 6.4), Peer Update (Section 7.5), 6.5),
   Destination Up (Section 7.9), 6.9), Destination Update (Section 7.13) 6.13) and
   Link Characteristics ACK (Section 7.16) 6.16) signals to indicate the
   amount of recources resources for reception (with 0 meaning 'no resources
   available', and 100 meaning 'all resources available') at the
   destination.  The list of resources that might be considered is
   beyond the scope of this document, and is left to implementations to
   decide.

   The Resources (Receive) 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     |     RESR      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1

   Resources (Receive):  A  An 8-bit integer percentage, 0-100,
      representing the amount of resources allocated to receiving data.

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

8.19.

7.20.  Resources (Transmit)

   The Resources (Receive) (RESR) (Transmit) (REST) data item MAY appear in the Peer
   Initialization ACK signal (Section 7.4), 6.4), Peer Update (Section 7.5), 6.5),
   Destination Up (Section 7.9), 6.9), Destination Update (Section 7.13) 6.13) and
   Link Characteristics ACK (Section 7.16) 6.16) signals to indicate the
   amount of recources resources for transmission (with 0 meaning 'no resources
   available', and 100 meaning 'all resources available') at the
   destination.  The list of resources that might be considered is
   beyond the scope of this document, and is left to 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  An 8-bit integer percentage, 0-100,
      representing the amount of resources allocated to transmitting
      data.

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

8.20.

7.21.  Relative Link Quality (Receive)

   The Relative Link Quality (Receive) (RLQR) data item MAY appear in
   the Peer Initialization ACK signal (Section 7.4), 6.4), Peer Update
   (Section 7.5), 6.5), Destination Up (Section 7.9), 6.9), Destination Update
   (Section 7.13) 6.13) and Link Characteristics ACK (Section 7.16) 6.16) signals to
   indicate the quality of the link for receiving data as calculated by
   the originating peer. data.

   The Relative Link Quality (Receive) 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     |     RLQR      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Data Item Type:  TBD

   Length:  1

   Relative Link Quality (Receive):  A non-dimensional 8-bit 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.

7.22.  Relative Link Quality (Transmit)

   The Relative Link Quality (Transmit) (RLQT) data item MAY appear in
   the Peer Initialization ACK signal (Section 7.4), 6.4), Peer Update
   (Section 7.5), 6.5), Destination Up (Section 7.9), 6.9), Destination Update
   (Section 7.13) 6.13) and Link Characteristics ACK (Section 7.16) 6.16) signals to
   indicate the quality of the link for transmitting data as calculated
   by the originating peer. data.

   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 8-bit integer,
      1-100, representing relative link quality.  A value of 100
      represents a link of the highest quality.

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

8.22.

7.23.  Link Characteristics ACK Timer

   The Link Characteristics ACK Timer data item MAY appear in the Link
   Characterisitics
   Characteristics Request signal (Section 7.15) 6.15) to indicate the desired
   number of seconds to the 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 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 Type|    Length = 1     | Interval      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1

   Interval:  0 = Do NOT use timeouts for this Link Characteristics requests
      on this router/modem session.
      request.  Non-zero = Interval, in seconds, to wait before
      considering a this Link Characteristics Request has been lost.

9.

8.  Credit-Windowing

   DLEP includes an OPTIONAL Protocol Extension for a credit-windowing
   scheme analogous to the one documented in [RFC5578].  In this scheme,
   traffic between the router and modem is treated as two unidirectional
   windows.  This document identifies these windows as the 'Modem
   Receive Window', or
   MRW, Window' (MRW), and the 'Router Receive Window', or RRW. Window' (RRW).

   If the OPTIONAL credit-windowing scheme extension is used, credits MUST be
   granted by the receiver on a given window - that is, on the 'Modem
   Receive Window' (MRW), the modem is responsible for granting credits
   to the router, allowing it (the router) to send data to the modem.
   Likewise, the router is responsible for granting credits on the RRW,
   which allows the modem to send data to the router.

   DLEP expresses all credit data in number of octets.  The total number
   of credits on a window, and the increment to add to a grant, are
   always expressed as a 64-bit unsigned integer quantity.

   If used, credits

   Credits are managed on a neighbor-specific destination-specific basis; that is,
   separate credit counts are maintained for each neighbor destination requiring
   the service.  Credits do not apply to the DLEP session that exists
   between routers and modems.

   If a peer is able to support the OPTIONAL credit-windowing scheme extension
   then it MUST include a Extensions Supported data item (Section 8.6) 7.7)
   including the value DLEP_EXT_CREDITS (value TBD) in the appropriate
   Peer Initialization or Peer Initialization ACK signal.

9.1.

8.1.  Credit-Windowing Signals

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

9.1.1.

8.1.1.  Destination 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. 8.2.1)

   If the Destination Up signal does not contain the Credit Grant data
   item, credits MUST NOT be used for that destination.

8.1.2.  Destination Up ACK Signal

   The

   If the corresponding Destination Up signal contained the Credit Grant
   data item, the Destination Up ACK signal MAY MUST contain one of each of
   the following data items:

   o  Credit Window Status (Section 9.2.1)

9.1.3. 8.2.2)

8.1.3.  Destination Update Signal

   The

   If the corresponding Destination Up signal contained the Credit Grant
   data item, the Destination Update signal MAY MUST contain one of each of
   the following data items:

   o  Credit Window Status (Section 9.2.1) 8.2.2)

   If the corresponding Destination Up signal contained the Credit Grant
   data item, the Destination Update signal MAY contain one of each of
   the following data items:

   o  Credit Grant (Section 9.2.2) 8.2.1)

   o  Credit Request (Section 9.2.3)

9.2. 8.2.3)

8.2.  Credit-Windowing Data Items

   The credit-windowing scheme extension introduces 3 additional data items.
   If a peer has advertised during session initialization that it
   supports the credit-windowing scheme extension then it MUST correctly
   process the following data items without error.

          +------------+-----------------------+----------------+
          | Data Item  | Description           | Section        |
          +------------+-----------------------+----------------+
          | TBD        | Credit Window Status Grant          | Section 9.2.1 8.2.1  |
          | TBD        | Credit Grant Window Status  | Section 9.2.2 8.2.2  |
          | TBD        | Credit Request        | Section 9.2.3 8.2.3  |
          +------------+-----------------------+----------------+

9.2.1.

8.2.1.  Credit Window Status

   If the credit-window scheme Grant

   The Credit Grant data item is supported by the sent from a DLEP participants
   (both participant to grant
   an increment to credits on a window.  The Credit Grant data item MAY
   appear in the router Destination Up (Section 6.9) and the modem), the Destination Update
   (Section 6.13) signals.  The value in a Credit Window Status Grant data item
   MUST
   represents an increment to be sent by added to any existing credits available
   on the participant receiving window.  Upon successful receipt and processing of a Credit
   Grant for data item, the receiver MUST respond with a signal containing 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 current (or initial) number of credits available on the Router
      Receive Window.

9.2.2.  Credit Grant

   The Credit Grant data item is sent from a DLEP participant to grant
   an increment to credits on a window.  The Credit Grant data item MAY
   appear in the Destination Up (Section 7.9) or Destination Update
   (Section 7.13) signals.  The value in a Credit Grant data item
   represents an increment to be added to any existing credits available
   on the window.  Upon successful receipt and processing of a Credit
   Grant data item, the receiver MUST respond with a signal containing a
   Credit Window Status data item to report to report the updated aggregate values
   for synchronization purposes. purposes, and if initializing a new credit
   window, granting initial credits.

   In the Destination Up signal, when credits are 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 an initial, non-zero value.  If the receiver of a Destination Up
   signal with a Credit Grant data item supports credits, the receiver
   MUST either reject the use of credits, credits for this destination, via a
   Destination Up ACK response containing a Status data item
   (Section 8.2) 7.2) with a status code of 'Request Denied', or set the
   initial value from the data contained in the Credit Window Status
   data item.  If the initialization completes successfully, the
   receiver MUST respond to the Destination Up signal with a Destination
   Up ACK signal that contains a Credit Window Status data item,
   initializing its receive window.

   The Credit Grant 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     |       Credit Increment        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Credit Increment                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Credit Increment         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  8

   Reserved:  A 64-bit unsigned integer representing the additional
      credits to be assigned to the 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 derived from
   the sender of the grant.  The Credit Increment MUST NOT cause the
   window to overflow; if this condition occurs, implementations MUST
   set the credit window to the maximum value contained in a 64-bit
   quantity.

9.2.3.

8.2.2.  Credit Request

   The Credit Request data item MAY be sent from either DLEP
   participant, via the Destination Window Status

   If the credit-window extension is supported by the DLEP participants
   (both the router and the modem), the Credit Window Status data item
   MUST be sent by the 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     | 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 number of credits available on the Modem Receive
      Window, for the destination referred to by the signal.

   Router Receive Window Value:  A 64-bit unsigned integer, indicating
      the current number of credits available on the Router Receive
      Window, for the destination referred to by the signal.

8.2.3.  Credit Request

   The Credit Request data item MAY be sent from either DLEP
   participant, via the Destination Update signal (Section 7.13), 6.13), to
   indicate the desire for the partner to grant additional credits in
   order for data transfer to proceed on the session.  If the
   corresponding Destination Up signal (Section 7.9) 6.9) for this session
   did NOT contain a Credit Window Status data item, indicating that
   credits are to be used on the session, then the Credit Request data
   item MUST be rejected silently dropped by the receiver via a Destination Update ACK
   signal containing a Status data item (Section 8.2) with status code
   'Request Denied'. receiver.

   The Credit Request 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     | Reserved, MUST|
   |               |               | be set to 0   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD

   Length:  1

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

10.

9.  Security Considerations

   The protocol does not contain any mechanisms for security (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.

11.

10.  IANA Considerations

   This section specifies requests to IANA.

11.1.

10.1.  Registrations

   This specification defines:

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

   o  Reservation of numbering space for Experimental DLEP signals.

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

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

   o  A new repository for DLEP status codes. codes, with seven currently
      assigned.

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

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

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

11.2.

10.2.  Expert Review: Evaluation Guidelines

   No additional guidelines for expert review are anticipated.

11.3.

10.3.  Signal 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.

11.4.

10.4.  DLEP Data Item Registrations

   A new repository for DLEP data items must be created.

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

   Valid data items are:

   o  DLEP Version

   o  Status

   o  DLEP Port  IPv4 Connection Point

   o  IPv6 Connection Point

   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  Link Characteristics ACK Timer

   o  Credit Window Status

   o  Credit Grant

   o  Credit Request

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

11.5.

10.5.  DLEP 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 Data

   o  Unexpected Signal

   o  Request Denied

   o  Timed Out

11.6.

   o  Invalid Destination

10.6.  DLEP 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.

10.7.  DLEP Well-known Port

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

11.8.

10.8.  DLEP Multicast Address

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

12.

11.  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 influence and
   contributions of Greg Harrison, Chris Olsen, Martin Duke, Subir Das,
   Jaewon Kang, Vikram Kaul, and Nelson Powell.

13. Powell and Victoria Mercieca.

12.  References

13.1.

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for 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 Credit
              Flow and Link Metrics", RFC 5578, February 2010.

13.2.

12.2.  Informative References

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

Appendix A.  Peer Level Signal Flows

   _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 discovery, starts
|                                     a problem, sends
   w/ Non-zero Status TLV timer, send Peer Offer w/Status TLV indicating
                                      the error. Discovery
|-------Peer Discovery---->||         signal.

         ~ ~ ~ ~ ~ ~ ~                Router accepts failure, restarts discovery process.

--------Peer Discovery--------> timer expires
                                      without receiving Peer Offer.

|                                     Router initiates discovery

 <--------Peer Offer------------      Modem accepts, sends another Peer Offer
                                      w/Zero Status TLV indicating
                                      success.
|-------Peer Discovery---------->|    Discovery completed.

A.2.  Router Device Detects Peer Offer Timeout

Router signal.
                                 |
                                 |    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------------ receives Peer Discovery
                                 |    signal.
                                 |
                                 |    Modem accepts, sends Peer Offer
                                      w/Zero Status TLV indicating
                                      success.

                                      Discovery completed.

A.3. with
|<--------Peer Offer-------------|    Connection Point information.
:
:                                     Router MAY cancel discovery timer
:                                     and stop sending Peer Offer Lost Discovery
:                                     signals.

A.2.  Session Initialization

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

 <-------Peer Discovery---------
========================================================================

|                                     Router connects to discovered or
|                                     pre-configured Modem initiates discovery, starts
                                       a guard timer.

  ---------Peer Offer-------|| Connection
|---------TCP connect---------->      Point.
|
|                                     Router offers availability sends Peer Initialization
|-------Peer Initialization----->|    signal.
                                 |
                                 |    Modem times out on receives Peer Offer,
                                       restarts discovery process.

 <-------Peer Discovery--------- Initialization
                                 |    signal.
                                 |
                                 |    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.

A.4.  Discovery Initialization
                                 |    ACK, with compatible extensions,
|<----Peer Initialization ACK----|    and Success status data item.
|                                |
|<<============================>>|    Session established. Heartbeats
:                                :    begin.

A.3.  Session Initialization - Refused

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

 <-------Peer Discovery---------
========================================================================

|                                     Router connects to discovered or
|                                     pre-configured Modem initiates discovery

  ---------Peer Offer-----------> Connection
|---------TCP connect---------->      Point.
|
|                                     Router offers availability

 <-----Peer Initialization------ sends Peer Initialization
|-------Peer Initialization----->|    signal.
                                 |
                                 |    Modem Connects on receives Peer Initialization
                                 |    signal, and will not support the
                                 |    advertised version, experiment or
                                 |    extensions.
                                 |
                                 |    Modem sends Peer Initialization
                                 |    ACK, with 'Request Denied' status
|<----Peer Initialization ACK----|    data item.
|                                |
|  <---- 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

A.5. shutdown (send)-----|    Modem closes TCP connection.
|
|                                     Router Detects a Heartbeat timeout receives negative Peer
|                                     Initialization ACK, closes
|---------TCP close----------->       TCP connection.
|
||------------------------------||    Session not started.

A.4.  Router Changes IP Addresses

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 ---------> sends Peer Terminate Request Update signal to
|--------Peer Update------------>|    announce change of IP address
                                 |
                                 |    Modem takes down all destination
                                      sessions, then acknowledges the receives Peer Terminate

<----Peer Terminate ACK--------- Update signal
                                 |    and updates internal state.
                                 |
|<-------Peer Update ACK---------|    Modem sends Peer Terminate ACK

A.6. Update ACK.

A.5.  Modem Detects a Heartbeat timeout Changes Session-wide Metrics
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-------- sends Peer Terminate Request Update signal to
                                 |    announce change of modem-wide
|<--------Peer Update------------|    metrics
|
|                                     Router takes down all destination
                                       sessions, then acknowledges the
                                       Peer Terminate

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

A.7. Update signal
|                                     and updates internal state.
|
|-------Peer Update ACK--------->|    Router sends Peer Terminate (from Modem) Lost Update ACK.

A.6.  Router Terminates Session

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

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

|                                     Router Heartbeat times out,
                                         terminates association.

   --------Peer Terminate-------> sends Peer Termination
|-------Peer Termination-------->|    signal with Status data item.
|                                |
|-------TCP shutdown (send)--->  |    Router stops sending signals.
                                 |
                                 |    Modem receives Peer Terminate

   <-----Peer Terminate ACK------ Termination,
                                 |    stops counting received heartbeats
                                 |    and stops sending heartbeats.
                                 |
                                 |    Modem sends Peer Terminate Termination ACK

A.8.  Peer Terminate (from Router) Lost
|<-----Peer Termination ACK------|    with Status 'Success'.
|                                |
|  <----TCP shutdown (send)------|    Modem stops sending signals.
|
||------------------------------||    Session terminated.

A.7.  Modem Terminates Session
Router                       Modem    Signal Description
   ====================================================================

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

                                 |    Modem HB times out,
                                         terminates association.

   <------Peer Terminate-------- sends Peer Termination
|<------Peer Termination---------|    signal with Status data item.
|                                |
|  <----TCP shutdown (send)------|    Modem stops sending signals.
|
|                                     Router receives Peer Terminate

   ------Peer Terminate ACK-----> Termination,
|                                     stops counting received heartbeats
|                                     and stops sending heartbeats.
|
|                                     Router sends Peer Terminate Termination ACK

Appendix B.  Destination Specific Signal Flows

B.1.  Modem Destination Up Lost
|------Peer Termination ACK----->|    with Status 'Success'.
|                                |
|-------TCP shutdown (send)--->  |    Router stops sending signals.
                                 |
||------------------------------||    Session terminated.

A.8.  Session Heartbeats
Router                       Modem    Signal Description
   ====================================================================

    ||-----Destination Up ------------   Modem
========================================================================

|----------Heartbeat------------>|    Router sends Destination Up

                                         Modem timesout on ACK

    <------Destination Up ------------ heartbeat signal
                                 |
                                 |    Modem sends Destination Up

    ------Destination Up ACK--------->   Router accepts resets heartbeats missed
                                 |    counter.

         ~ ~ ~ ~ ~ ~ ~

|----------[Any signal]--------->|    When the destination
                                         session

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

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

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

   ------Destination Up ACK-------||     Router accepts receives any signal
                                 |    from the destination
                                         session Router.
                                 |
                                 |    Modem timesout on ACK

   <------Destination Up ------------ resets heartbeats missed
                                 |    counter.

         ~ ~ ~ ~ ~ ~ ~

|<---------Heartbeat-------------|    Modem resends Destination Up sends heartbeat signal
|
|                                     Router detects duplicate
                                         Destination, takes down the
                                         previous, accepts resets heartbeats missed
|                                     counter.

         ~ ~ ~ ~ ~ ~ ~

|<---------[Any signal]----------|    When the new
                                         Destination.

   ------Destination Up ACK---------> Router accepts receives any
|                                     signal from the destination
                                         session

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

B.3.  Destination Up, No Layer 3 Addresses resets heartbeats missed
|                                     counter.

A.9.  Router Detects a Heartbeat timeout

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

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

  ------Destination Up ACK--------->
========================================================================

        ||<----------------------|    Router accepts the destination
                                        session misses a heartbeat

|       ||<----------------------|    Router ARPs for IPv4 if defined. misses too many heartbeats
|
|
|-------Peer Termination-------->|    Router drives ND for IPv6 if
                                        defined.

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

B.4.  Destination Up sends Peer Termination
|                                     signal with IPv4, No IPv6 'Timeout' Status
|                                     data item.
:
:                                     Termination proceeds as above.

A.10.  Modem Detects a Heartbeat timeout

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--------- misses a heartbeat

|---------------------->||       |    Modem Destination Metrics
          . . . . . . . .
   <------Destination Update--------- misses too many heartbeats
                                 |
                                 |
|<-------Peer Termination--------|    Modem sends Peer Termination
                                 |    signal with 'Timeout' Status
                                 |    data item.
                                 :
                                 :    Termination proceeds as above.

Appendix B.  Destination Metrics

B.5. Specific Signal Flows

B.1.  Common Destination Up with IPv4 and IPv6 Signaling

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

   <------Destination Up ------------
========================================================================

                                 |    Modem detects a new logical
                                 |    destination is reachable, and
|<-------Destination Up----------|    sends Destination Up with
                                         the IPv4 and IPv6 TLVs

   ------Destination signal.
|
|--------Destination Up ACK---------> ACK----->|    Router accepts the sends Destination Up ACK.

           ~ ~ ~ ~ ~ ~ ~
                                 |    Modem detects change in logical
                                 |    destination
                                         session

   <------Destination Update--------- metrics, and sends
|<-------Destination Update------|    Destination Update signal.

           ~ ~ ~ ~ ~ ~ ~
                                 |    Modem detects change in logical
                                 |    destination metrics, and sends
|<-------Destination Update------|    Destination Metrics
          . . . . . . . .

B.6. Update signal.

            ~ ~ ~ ~ ~ ~ ~
                                 |    Modem detects logical destination
                                 |    is no longer reachable, and sends
|<-------Destination Down--------|    Destination Session Success Down signal.
|
|                                     Router receives Destination Down,
|                                     updates internal state, and sends
|--------Destination Down ACK--->|    Destination Down ACK signal.

B.2.  Multicast Destination Signaling

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

   ---------Peer Offer----------->
========================================================================

|                                     Router offers availability

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

   <------Destination detects a new multicast
|                                     destination is in use, and sends
|--------Destination Up--------->|    Destination Up ----------- signal.
                                 |
                                 |    Modem

   ------Destination updates internal state to
                                 |    monitor multicast destination, and
|<-------Destination Up ACK-------->     Router

   <------Destination Update---------    Modem
          . . . . . . . .
   <------Destination Update--------- ACK------|    sends Destination Up ACK.

           ~ ~ ~ ~ ~ ~ ~
                                 |    Modem detects change in multicast
                                 |    destination metrics, and sends
|<-------Destination Update------|    Destination Update signal.

           ~ ~ ~ ~ ~ ~ ~
                                 |    Modem initiates the terminate

   <------Destination detects change in multicast
                                 |    destination metrics, and sends
|<-------Destination Update------|    Destination Update signal.

            ~ ~ ~ ~ ~ ~ ~
|                                     Router detects multicast
|                                     destination is no longer in use,
|--------Destination Down------->|    and sends Destination Down ---------- signal.
                                 |
                                 |    Modem

   ------Destination receives Destination Down,
                                 |    updates internal state, and sends
|<-------Destination Down ACK-------> ACK----|    Destination Down ACK signal.

B.3.  Link Characteristics Request
Router

                                         or                       Modem    Signal Description
========================================================================

                                      Destination has already been
           ~ ~ ~ ~ ~ ~ ~              announced by either peer.

|                                     Router initiates requires different
|                                     Characteristics for the terminate

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

   <------Destination Down ACK-------
|                                     destination, and sends Link
|--Link Characteristics Request->|    Characteristics Request signal.
                                 |
                                 |    Modem attempts to adjust link
                                 |    status to meet the received
                                 |    request, and sends a Link
                                 |    Characteristics Request ACK
|<---Link Char. Request ACK------|    signal with the new values.

Authors' Addresses

   Stan Ratliff
   VT iDirect
   13861 Sunrise Valley Drive, Suite 300
   Herndon, VA  20171
   USA

   Email: sratliff@idirect.net

   Bo Berry

   Shawn Jury
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: sjury@cisco.com

   Darryl Satterwhite
   Broadcom

   Email: dsatterw@broadcom.com
   Rick Taylor
   Airbus Defence & Space
   Quadrant House
   Celtic Springs
   Coedkernew
   Newport  NP10 8FZ
   UK

   Email: rick.taylor@airbus.com