MPLS Working Group WG                                          Bilel Jamoussi, Editor
Internet Draft                                    Nortel Networks Corp.
Expiration Date: August 1999 February 2000
                                                            August 1999

                  Constraint-Based LSP Setup using LDP

                     draft-ietf-mpls-cr-ldp-01.txt

                     draft-ietf-mpls-cr-ldp-02.txt

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Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   Label Distribution Protocol (LDP) is defined in [LDP] [1] for distribution
   of labels inside one MPLS domain.  One of the most important
   services that may be offered using MPLS in general and LDP in
   particular is support for constraint-based routing of traffic across
   the routed network. Constraint-based routing offers the opportunity
   to extend the information used to setup paths beyond what is
   available for the routing protocol. For instance, an LSP can be
   setup based on explicit route constraints, QoS constraints, and
   others.
   other constraints. Constraint-based routing (CR) is a mechanism used
   to meet Traffic Engineering requirements that have been proposed by [FRAME],
   [ARCH]
   [2], [3] and [TER]. [4]. These requirements may be met by extending LDP for
   support of constraint-based routed label switched paths (CRLSPs).

CR-LDP Specification             - 2 -                  Exp. August 1999
   Other uses exist for CRLSPs as well ([VPN1], [VPN2] ([5], [6] and [VPN3]). [7]).

   This draft specifies mechanisms and TLVs for support of CRLSPs using
   LDP. The Explicit Route object and procedures are extracted from
   [ER].
   [8].

Table of Contents

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   1.         Introduction .........................................   3 Introduction....................................................3
   2. Constraint-based Routing Overview ....................   3 Overview...............................3
   2.1 Strict and Loose Explicit Routes .....................   4 Routes...............................3
   2.2 Traffic Characteristics ..............................   4 Characteristics........................................4
   2.3        Pre-emption ..........................................   5 Pre-emption....................................................4
   2.4 Route Pinning ........................................   5 Pinning..................................................5
   2.5 Resource Class .......................................   5 Class.................................................5
   3. Solution Overview ....................................   5 Overview...............................................5
   3.1 Required Messages and TLVs ...........................   7 TLVs.....................................6
   3.2 Label Request Message ................................   7 Message..........................................7
   3.3 Label Mapping Message ................................   8 Message..........................................7
   3.4 Notification Message .................................   9 Message...........................................8
   3.5 Release & Withdraw Messages ..........................   9 , Withdraw, and Abort Messages.........................9
   4. Protocol Specification  ..............................   9 Specification..........................................9
   4.1 Explicit Route TLV (ER-TLV)  .........................  10 (ER-TLV)....................................9
   4.2 Explicit Route Hop TLV  ..............................  10 (ER-Hop TLV)...........................10
   4.3 Traffic Parameters TLV  ..............................  12 TLV........................................11
   4.3.1      Semantics  ...........................................  13 Semantics...................................................13
   4.3.1.1    Frequency  ...........................................  13 Frequency.................................................13
   4.3.1.2 Peak Rate  ...........................................  14 Rate.................................................13
   4.3.1.3 Committed Rate  ......................................  14 Rate............................................13
   4.3.1.4 Excess Burst Size ....................................  14 Size.........................................14
   4.3.1.5 Peak Rate Token Bucket................................  14 Bucket....................................14
   4.3.1.6 Committed Data Rate Token Bucket .....................  15 Bucket..........................14
   4.3.1.7    Weight ......................... .....................  16 Weight....................................................15
   4.3.2      Procedures ...........................................  16 Procedures..................................................15
   4.3.2.1 Label Request Message ................................  16 Message.....................................15
   4.3.2.2 Label Mapping Message ................................  16 Message.....................................16
   4.3.2.3 Notification Message .................................  17 Message......................................16
   4.4 Preemption TLV .......................................  18 TLV................................................16
   4.5 LSPID TLV  ...........................................  18 TLV.....................................................17
   4.6 Resource Class TLV  ..................................  19 (Color) TLV....................................18
   4.7 ER-Hop Semantics .....................................  19
   4.7.1 semantics..............................................19
   4.7.1. ER-Hop 1 TLV 1: The IPv4 Prefix .............................  20
   4.7.2 prefix..................................19
   4.7.2. ER-Hop 2 TLV 2: The IPv6 Prefix .............................  20
   4.7.3 address.................................19
   4.7.3. ER-Hop 3 TLV AS Number ...............................  21
   4.7.4 3:  The autonomous system number....................20
   4.7.4. ER-Hop 4 TLV LSPID ...................................  21
   4.8 4: LSPID............................................20
   4.8. Processing of the ER-TLV .............................  22
   4.8.1 Explicit Route TLV.........................22
   4.8.1. Selection of the next hop ............................  22
   4.8.2 hop..................................22
   4.8.2. Adding the Label Request Message ER-Hops to the next hop .....  24 explicit route TLV...................23
   4.9 Route Pinning TLV  ...................................  24 TLV.............................................23
   4.10       CR-LSP CRLSP FEC Element ...................................  24 Element............................................24
   4.11 Error Subcodes  ......................................  25

CR-LDP Specification             - 3 -                  Exp. August 1999 subcodes...............................................24
   5.         Security Considerations ..............................  26 Security.......................................................25
   6.         Acknowledgement ......................................  26 Acknowledgments................................................25
   7.         References ...........................................  26 Intellectual Property Consideration............................25
   8.         Author Information ...................................  28 References.....................................................25
   9. Author's Addresses.............................................26
   Appendix A A: CRLSP Establishment Examples .........................  30 Examples..........................29
   A.1 Strict Explicit Route Example ........................  30
   A.2 Example.................................29
   A.2. Node Groups and Specific Nodes Example ...............  31 Example.......................30

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   Appendix B B. QoS Service Examples .................................  34 Examples..................................33
   B.1 Service Examples .....................................  34
   B.2 Examples..............................................33
   B.2. Establishing CR-LSP Supporting Real-Time Applications.  35
   B.3 Applications........34
   B.3. Establishing CR-LSP Supporting Delay Insensitive Applications ...  36 Applications35

1. Introduction

   The need for constraint-based routing (CR) in MPLS has been explored
   elsewhere [ARCH], [FRAME], [3], [2], and [TER]. [4].  Explicit routing is a subset of the
   more general constraint-based routing function. At the MPLS WG
   meeting held during the Washington IETF (December 1997) there was
   consensus that LDP should support explicit routing of LSPs with
   provision for indication of associated (forwarding) priority.  In
   the Chicago meeting, meeting (August 1998), a decision was made that support
   for explicit path setup in LDP will be moved to a separate document.
   This document provides that support and it has been accepted as a
   working document in the Orlando meeting. meeting (December 1998).

   This specification proposes an end-to-end setup mechanism of a
   constraint-based routed LSP (CRLSP) initiated by the ingress LSR. We
   also specify mechanisms to provide means for reservation of
   resources using LDP.

   This document introduce TLVs and procedures that provide support
   for:
        - Strict and Loose Explicit Routing
        - Specification of Traffic Parameters
        - Route Pinning
        - CRLSP Pre-emption though setup/holding priorities
        - Handling Failures
        - LSPID
        - Resource Class

   Section 2 introduces the various constraints defined in this
   specification. Section 3 outlines the CR-LDP solution. Section 4
   defines the TLVs and procedures used to setup constraint-based
   routed label switched paths.  Appendix A provides several examples
   of CR-LSP path setup. Appendix B provides Service Definition
   Examples.

2. Constraint-based Routing Overview

   Constraint-based routing is a mechanism that supports the Traffic
   Engineering requirements defined in [TER]. [4]. Explicit Routing is a
   subset of the more general constraint-based routing where the

CR-LDP Specification             - 4 -                  Exp. August 1999
   constraint is the explicit route (ER). Other constraints are defined
   to provide a network operator with control over the path taken by an
   LSP. This section is an overview of the various constraints
   supported by this specification.

2.1 Strict and Loose Explicit Routes

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   Like any other LSP an CRLSP is a path through an MPLS network. The
   difference is that while other paths are setup solely based on
   information in routing tables or from a management system, the
   constraint-based route is calculated at one point at the edge of
   network based on criteria, including but not limited to routing
   information. The intention is that this functionality shall give
   desired special characteristics to the LSP in order to better
   support the traffic sent over the LSP. The reason for setting up
   CRLSPs, might be that one wants to assign certain bandwidth or other
   Service Class characteristics to the LSP, or that one wants to make
   sure that alternative routes use physically separate paths through
   the network.

   An explicit route is represented in a Label Request Message as a
   list of nodes or groups of nodes along the constraint-based route.
   When the CRLSP is established, all or a subset of the nodes in a
   group may be traversed by the LSP.  Certain operations to be
   performed along the path can also be encoded in the constraint-based
   route.

   The capability to specify, in addition to specified nodes, groups of
   nodes, of which a subset will be traversed by the CRLSP, allows the
   system a significant amount of local flexibility in fulfilling a
   request for a constraint-based route.  This allows the generator of
   the constraint-based route to have some degree of imperfect
   information about the details of the path.

   The constraint-based route is encoded as a series of ER-Hops
   contained in a constraint-based route TLV.  Each ER-Hop may identify
   a group of nodes in the constraint-based route. A constraint-based
   route is then a path including all of the identified groups of
   nodes.

   To simplify the discussion, we call each group of nodes an abstract
   node.  Thus, we can also say that a constraint-based route is a path
   including all of the abstract nodes, with the specified operations
   occurring along that path.

2.2 Traffic Characteristics

   The traffic characteristics of a path are described in the Traffic
   Parameters TLV in terms of a peak rate, committed rate, and service
   granularity. The peak and committed rates describe the bandwidth
   constraints of a path while the service granularity can be used to
   specify a constraint on the delay variation that the CRLDP MPLS
   domain may introduce to a path's traffic.

CR-LDP Specification             - 5 -                  Exp. August 1999

2.3 Pre-emption

   CR-LDP signals the resources required by a path on each hop of the
   route. If a route with sufficient resources can not be found,
   existing paths may be rerouted to reallocate resources to the new

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   path. This is the process of path pre-emption. Setup and holding
   priorities are used to rank existing paths (holding priority) and
   the new path (setup priority) to determine if the new path can pre-empt pre-
   empt an existing path.

   The setupPriority of a new CRLSP and the holdingPriority attributes
   of the existing CRLSP are used to specify priorities. Signaling a
   higher holding priority expresses express that the path, once it has been
   established, should have a lower chance of being pre-empted.
   Signaling a higher setup priority expresses the expectation that, in
   the case that resource are unavailable, the path is more likely to
   pre-empt other paths. The exact rules determining bumping are an
   aspect of network policy.

   The allocation of setup and holding priority values to paths is an
   aspect of network policy.

   The setup and holding priority values range from zero (0) to seven
   (7). The value zero (0) is the priority assigned to the most
   important path. It is referred to as the highest priority. Seven (7)
   is the priority for the least important path. The use of default
   priority values is an aspect of network policy.

   The setupPriority of a CRLSP should not be higher (numerically less)
   than its holdingPriority since it might bump an LSP and be bumped by
   next "equivalent" _equivalent_ request.

2.4 Route Pinning

   Route pinning is applicable to segments of an LSP that are loosely
   routed - i.e. those segments which are specified with a next hop
   with the 'L' `L' bit set or where the next hop is an "abstract node". _abstract node_.  A
   CRLSP may be setup using route pinning if it is undesirable to
   change the path used by an LSP because a better next hop becomes
   available at some LSR along the loosely routed portion of the LSP.

2.5 Resource Class

   Network resources

   The network operator may be classified in various ways by the classify network
   operator. resources in various ways.
   These classes are also known as "colors" _colors_ or "administrative
   groups". _administrative groups_.
   When an CR-LSP is being established, it's necessary to indicate
   which resource classes the CR-LSP can draw from.

3. Solution Overview

   CRLSP over LDP Specification is designed with the following goals:

CR-LDP Specification             - 6 -                  Exp. August 1999

        1. Meet the requirements outlined in [TER] [4] for performing traffic
           engineering and provide a solid foundation for performing
           more general constraint-based routing.

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        2. Build on already specified functionality that meets the
           requirements whenever possible. Hence, this specifications specification is
           based on [LDP] [1] and the Explicit Route object and procedures
           defined in [ER]. [8].

        3. Keep the solution simple.

   In this document, support for unidirectional point-to-point CRLSPs
   is specified. Support for point-to-multipoint, multipoint-to-point,
   is for further study (FFS).

   Support for constraint-based routed LSPs in this specification
   depends on the following minimal LDP behaviors as specified in [LDP]: [1]:

     -  Basic and/or Extended Discovery Mechanisms.
     -  Use the Label Request Message defined in [LDP] [1] in downstream on
        demand label advertisement mode with ordered control.
     -  Use the Label Mapping Message defined in [LDP] [1] in downstream on
        demand mode with ordered control.
     -  Use the Notification Message defined in [LDP]. [1].
     -  Use the Withdraw and Release Messages defined in [LDP]. [1].
     -  Use the Loop Detection (in the case of loosely routed segments
        of a CRLSP) mechanisms defined in [LDP]. [1].

   In addition, the following functionality is added to what's defined
   in [LDP]: [1]:

     -  The Label Request Message used to setup a CRLSP includes one or
        more CR-TLVs defined in Section 4. For instance, the Label
        Request Message may include the ER-TLV.

     -  An LSR implicitly infers ordered control from the existence of
        one or more CR-TLVs in the Label Request Message. This means
        that the LSR can still be configured for independent control
        for LSPs established as a result of dynamic routing. However,
        when a Label Request Message includes one or more of the CR-TLVs, CR-
        TLVs, then ordered control is used to setup the CRLSP. Note
        that this is also true for the loosely routed parts of a CRLSP.

     -  New status codes are defined to handle error notification for
        failure of established paths specified in the CR-TLV.

   Optional TLVs are not required in the CR-LDP Specification             - 7 -                  Exp. August 1999 messages for the
   messages to be compliant with the protocol.  Optional parameters CAN
   be required for a particular operation to work (or work correctly),
   however.

   Examples of CRLSP establishment are given in Appendix A to
   illustrate how the mechanisms described in this draft work.

3.1 Required Messages and TLVs

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   Any Messages, TLVs, and procedures not defined explicitly in this
   document are defined in the [LDP] Specification. LDP Specification [1]. The state
   transitions
   transitions, which relate to CR-LDP messages messages, can be found in [LDP-
   STATE]. [9].
   The following subsections are meant as a cross reference cross-reference to the [LDP] [1]
   document and indication of additional functionality beyond what's
   defined in [LDP] [1] where necessary.

3.2 Label Request Message

   The Label Request Message is as defined in 3.5.8 of [LDP] [1] with the
   following modifications (required only if any of the CR-TLVs is
   included in the Label Request Message):

     -  Only a single FEC-TLV may be included in the Label Request
        Message. The CR-LSP FEC TLV should be used.

     -  The Return Message ID TLV is MANDATORY.

      - The Optional Parameters TLV includes the definition of any of
        the Constraint-based TLVs specified in Section 4.

     -  The Procedures to handle the Label Request Message are
        augmented by the procedures for processing of the CR-TLVs as
        defined in Section 4.

   The encoding for the CR-LDP Label Request Message is as follows:

CR-LDP Specification             - 8 -                  Exp. August 1999

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |U|
   |0|   Label Request (0x0401)   |      Message Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Message ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     FEC TLV                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Return                     Message ID TLV  (mandatory)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     LSPID TLV            (CR-LDP, mandatory)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     ER-TLV               (CR-LDP, optional)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Traffic  TLV         (CR-LDP, optional)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Pinning TLV          (CR-LDP, optional)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Resource Class TLV (CR-LDP, optional)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Pre-emption  TLV     (CR-LDP, optional)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.3 Label Mapping Message

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   The Label Mapping Message is as defined in 3.5.7 of [LDP] [1] with the
   following modifications:

     -  Only a single Label-TLV may be included in the Label Mapping
        Message.

     -  The Label Mapping Message MUST include Label Request Message ID
      TLV.

      - The Label Mapping Message MUST include LSPID TLV.

      - The Label Mapping Message Procedures are limited to downstream
        on demand ordered control mode.

   A Mapping message is transmitted by a downstream LSR to an upstream
   LSR under one of the following conditions:

        1. The LSR is the egress end of the CRLSP and an upstream
           mapping has been requested.

        2. The LSR received a mapping from its downstream next hop LSR
           for an CRLSP for which an upstream request is still pending.

   The encoding for the CR-LDP Label Mapping Message is as follows:

CR-LDP Specification             - 9 -                  Exp. August 1999

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |U|
   |0|   Label Mapping (0x0400)   |      Message Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Message ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     FEC TLV                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Label TLV                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Label Request Message ID TLV  (mandatory)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     LSPID TLV            (CR-LDP, mandatory) optional)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Traffic  TLV         (CR-LDP, optional)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.4 Notification Message

   The Notification Message is as defined in Section 3.5.1 of [LDP] [1] and
   the Status TLV encoding is as defined in Section 3.4.7 of [LDP]. [1].
   Establishment of an Explicitly Routed LSP may fail for a variety of
   reasons.  All such failures are considered advisory conditions and
   they are signaled by the Notification Message.

   Notification Messages carry Status TLVs to specify events being
   signaled. New status codes are defined in Section 4.11 to signal
   error notifications associated with the establishment of a CRLSP and
   the processing of the CR-TLV.

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   The Notification Message must carry the LSPID TLV of the
   corresponding CRLSP.

   Notification Messages MUST be forwarded toward the LSR originating
   the Label Request at each hop and at any time that procedures in
   this specification - or in [1] - specify sending of a Notification
   Message in response to a Label Request Message.

   The encoding of the notification message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   Notification (0x0001)     |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Message ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Status (TLV)                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Optional Parameters                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.5 Release , Withdraw, and Withdraw Abort Messages

   The Label Release , Label Withdraw, and Label Withdraw Abort Request Messages
   are used as specified in [LDP] to clear CR-LSPs. [1]. These message messages may also carry the
   LSPID TLV.

4. Protocol Specification

   The Label Request Messages defined in [LDP] [1] optionally carries one or
   more of the optional Constraint-based Routing TLVs (CR-TLVs) defined
   in this section. If needed, other constraints can be supported later
   through the definition of new TLVs. In this specification, the
   following TLVs are defined:

     -  Explicit Route TLV

CR-LDP Specification             - 10 -                 Exp. August 1999
     -  Explicit Route Hop TLV
     -  Traffic Parameters TLV
     -  Preemption TLV
     -  LSPID TLV
     -  Route Pinning TLV
     -  Resource Class TLV
     -  CRLSP FEC TLV

4.1 Explicit Route TLV (ER-TLV)

   The ER-TLV is an object that specifies the path to be taken by the
   LSP being established. It is composed of one or more Explicit Route
   Hop TLVs (ER-Hop TLVs) defined in Section 4.2.

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   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|         ER-TLV  (0x0800)  |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ER-Hop TLV 1                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ER-Hop TLV 2                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                          ............                         ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ER-Hop TLV n                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

   Type
        A two byte two-byte field carrying the value of the ER-TLV type which
      is whichis
        0x800.

   Length
        Specifies the length of the value field in bytes.

   ER-Hop TLVs
        One or more ER-Hop TLVs defined in Section 4.2.

4.2 Explicit Route Hop TLV (ER-Hop TLV)

   The contents of an ER-TLV are a series of variable length ER-Hop
   TLVs.

   A node receiving a label request message including an ER-Hop type
   that is not supported should not progress the label request message
   to the downstream LSR and should send back a _No Route_ Notification
   Message.

   Each ER-Hop TLV has the form:

CR-LDP Specification             - 11 -                 Exp. August 1999

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|          ER-Hop-Type      |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |L|                                  Content //                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

   ER-Hop Type
        A fourteen-bit field indicating the type of contents of the ER-Hop. ER-
        Hop. Currently defined values are:

        Value Type
         ----- ------------------------
        0x801 IPv4 prefix
        0x802 IPv6 prefix

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        0x803 Autonomous system number
        0x804 LSPID

   Length
        Specifies the length of the value field in bytes.

   L bit
        The L bit is an attribute of the ER-Hop. The L bit is set if
        the ER-Hop ER-Hop represents a loose hop in the explicit route.
        If the bit is not set, the ER-Hop represents a strict hop in
        the explicit route.

        The L bit in the ER-Hop is a one-bit attribute.  If the L bit
        is set, then the value of the attribute is "loose." _loose._  Otherwise,
        the value of the attribute is "strict." _strict._  For brevity, we say
        that if the value of the ER-Hop attribute is loose then it is a "loose
      ER-Hop."
        _loose ER-Hop._  Otherwise, it's a "strict ER-Hop." _strict ER-Hop._  Further,
        we say that the abstract node of a strict or loose ER-Hop is a
        strict or a loose node, respectively.  Loose and strict nodes
        are always interpreted relative to their prior abstract nodes.
        The path between a strict node and its prior node MUST include
        only network nodes from the strict node and its prior abstract
        node.

        The path between a loose node and its prior node MAY include
        other network nodes nodes, which are not part of the strict node or
        its prior abstract node.

CR-LDP Specification             - 12 -                 Exp. August 1999

   Contents
        A variable length field containing the node or abstract node
        that is the consecutive nodes that make up the explicit routed
        LSP.

4.3 Traffic Parameters TLV

   The following sections describe the CRLSP Traffic Parameters.  The
   required characteristics of a CRLSP are expressed by the Traffic
   Parameter values.

   A Traffic Parameters TLV, is used to signal the Traffic Parameter
   values. The Traffic Parameters are defined in the subsequent
   sections.

   The Traffic Parameters TLV contains a Flags field, a Frequency, a
   Weight, and the five Traffic Parameters PDR, PBS, CDR, CBS, EBS.
   The Traffic Parameters TLV is shown below:

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   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0| Traf. Param. TLV  (0x0810)|      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |    Frequency  |     Reserved  |    Weight     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Peak Data Rate (PDR)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Peak Burst Size (PBS)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Committed Data Rate (CDR)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Committed Burst Size (CBS)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Excess Burst Size (EBS)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

   Type
        A fourteen-bit field carrying the value of the ER-TLV type
        which is 0x810.

   Length
        Specifies the length of the value field in bytes.

   Flags
        The Flags field is shown below:

CR-LDP Specification             - 13 -                 Exp. August 1999

         +--+--+--+--+--+--+--+--+
         | Res |F6|F5|F4|F3|F2|F1|
         +--+--+--+--+--+--+--+--+

        Res - These bits are reserved.
        Zero on transmission.
        Ignored on receipt.
        F1 - Corresponds to the PDR.
        F2 - Corresponds to the PBS.
        F3 - Corresponds to the CDR.
        F4 - Corresponds to the CBS.
        F5 - Corresponds to the EBS.
        F6 - Corresponds to the Weight.

        Each flag Fi is a Negotiable Flag corresponding to a Traffic
        Parameter. The Negotiable Flag value zero denotes NotNegotiable
        and value one denotes Negotiable.

   Frequency
        The Frequency field is coded as an 8 bit unsigned integer with
        the following code points defined:

                               0      -

        0- Unspecified
                               1      -
        1- Frequent
                               2      -

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        2- VeryFrequest 3-255  - Reserved Reserved
        Zero on transmission.  Ignored on receipt.

   Weight
        An 8 bit unsigned integer indicating the weight of the CRLSP.
        Valid weight values are from 1 to 255.  The value 0 means that
        weight is not applicable for the CRLSP.

   Traffic Parameters
        Each Traffic Parameter is encoded as a 32 bit 32-bit IEEE single-
        precision floating point floating-point number.  A value of positive infinity
        is represented as an IEEE single-precision floating-point
        number with an exponent of all ones (255) and a sign and
        mantissa of all zeros. The values PDR and CDR are in units of
        bytes per second. The values PBS, CBS and EBS are in units of
        bytes.

        The value of PDR MUST be greater than or equal to the value of
        CDR in a correctly encoded Traffic Parameters TLV.

4.3.1 Semantics

4.3.1.1 Frequency

CR-LDP Specification             - 14 -                 Exp. August 1999

   The Frequency specifies at what granularity the CDR allocated to the
   CRLSP is made available.  The value VeryFrequently means that the
   available rate should average at least the CDR when measured over
   any time interval equal to or longer than the shortest packet time
   at the CDR.  The value Frequently means that the available rate
   should average at least the CDR when measured over any time interval
   equal to or longer than a small number of shortest packet times at
   the CDR.

   The value Unspecified means that the CDR MAY be provided at any
   granularity.

4.3.1.2 Peak Rate

   The Peak Rate defines the maximum rate at which traffic SHOULD be
   sent to the CRLSP. The Peak Rate is useful for the purpose of
   resource allocation. If resource allocation within the MPLS domain
   depends on the Peak Rate value then it should be enforced at the
   ingress to the MPLS domain.

   The Peak Rate is defined in terms of the two Traffic Parameters PDR
   and PBS, see section 4.3.1.5 below.

4.3.1.3 Committed Rate

   The Committed Rate defines the rate that the MPLS domain commits to
   be available to the CRLSP.

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   The Committed Rate is defined in terms of the two Traffic Parameters
   CDR and CBS, see section 4.3.1.6 below.

4.3.1.4 Excess Burst Size

   The Excess Burst Size may be used at the edge of an MPLS domain for
   the purpose of traffic conditioning. The EBS MAY be used to measure
   the extent by which the traffic sent on a CRLSP exceeds the
   committed rate.

   The possible traffic conditioning actions, such as passing, marking
   or dropping, are specific to the MPLS domain.

   The Excess Burst Size is defined together with the Committed Rate,
   see section 4.3.1.6 below.

4.3.1.5 Peak Rate Token Bucket

   The Peak Rate of a CRLSP is specified in terms of a token bucket P
   with token rate PDR and maximum token bucket size PBS.

   The token bucket P is initially (at time 0) full, i.e., the token
   count Tp(0) = PBS.  Thereafter, the token count Tp, if less than
   PBS, is incremented by one PDR times per second. When a packet of
   size B bytes arrives at time t, the following happens:

CR-LDP Specification             - 15

     -                 Exp. August 1999

        o  If Tp(t)-B >= 0, the packet is not in excess of the peak  rate
        and Tp is decremented by B down to the minimum value of 0, else

        o

     -  the packet is in excess of the peak rate and Tp is not
        decremented.

   Note that according to the above definition, a positive infinite
   value of either PDR or PBS implies that arriving packets are never ever in
   excess of the peak rate.

   The actual implementation of a LSR doesn't need to be modeled
   according to the above formal token bucket specification.

4.3.1.6 Committed Data Rate Token Bucket

   The committed rate of a CRLSP is specified in terms of a token
   bucket C with rate CDR.  The extent by which the offered rate
   exceeds the committed rate MAY be measured in terms of another token
   bucket E, which also operates at rate CDR.  The maximum size of the
   token bucket C is CBS and the maximum size of the token bucket E is
   EBS.

   The token buckets C and E are initially (at time 0) full, i.e., the
   token count Tc(0) = CBS and the token count Te(0) = EBS.
   Thereafter, the token counts Tc and Te are updated CDR times per
   second as follows:

        o

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     -  If Tc is less than CBS, Tc is incremented by one, else

        o
     -  if Te is less then EBS, Te is incremented by one, else

        o
     -  neither Tc nor Te is incremented.

   When a packet of size B bytes arrives at time t, the following
   happens:

        o

     -  If Tc(t)-B >= 0, the packet is not in excess of the Committed
        Rate and Tc is decremented by B down to the minimum value of 0,
        else

        o
     -  if Te(t)-B >= 0, the packet is in excess of the Committed Rate rate
        but is not in excess of the EBS and Te is decremented by B down
        to the minimum value of 0, else

        o
     -  the packet is in excess of both the Committed Rate and the EBS
        and neither Tc nor Tc is decremented.

   Note that according to the above specification, a CDR value of
   positive infinity implies that arriving packets are never in excess
   of either the Committed Rate or EBS. A positive infinite value of
   either CBS or EBS implies that the respective limit cannot be

CR-LDP Specification             - 16 -                 Exp. August 1999
   exceeded.

   The actual implementation of a LSR doesn't need to be modeled
   according to the above formal specification.

4.3.1.7 Weight

   The weight determines the CRLSP's relative share of the possible
   excess bandwidth above its committed rate.  The definition of
   "relative share"
   _relative share_ is MPLS domain specific.

4.3.2 Procedures

4.3.2.1 Label Request Message

   If an LSR receives an incorrectly encoded Traffic Parameters TLV in
   which the value of PDR is less than the value of CDR then it MUST
   send a Notification Message including the Status code Traffic
   Parameters Unavailable to the upstream LSR from which it received
   the erroneous message.

   If a Traffic Parameter is indicated as Negotiable in the Label
   Request Message by the corresponding Negotiable Flag then an LSR MAY
   replace the Traffic Parameter value with a smaller value.

   If the Weight is indicated as Negotiable in the Label Request
   Message by the corresponding Negotiable Flag then an LSR may adjust
   replace the Weight value with a lower value (down to 1). 0).

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   If, after possible Traffic Parameter negotiation, an LSR can support
   the CRLSP Traffic Parameters then the LSR MUST reserve the
   corresponding resources for the CRLSP.

   If, after possible Traffic Parameter negotiation, an LSR cannot
   support the CRLSP Traffic Parameters then the LSR MUST send a
   notification message that contains the Resource Unavailable status
   code.

4.3.2.2 Label Mapping Message

   If an LSR receives an incorrectly encoded Traffic Parameters TLV in
   which the value of PDR is less than the value of CDR then it MUST
   send a Label Release message containing the Status code Traffic
   Parameters Unavailable to the LSR from which it received the
   erroneous message.

   The

   If the negotiation flag was set in the label request message, the
   egress LSR MUST include the (possibly negotiated) Traffic Parameters
   and Weight in the Label Mapping message.

   The Traffic Parameters and the Weight in a Label Mapping message
   MUST be forwarded unchanged.

CR-LDP Specification             - 17 -                 Exp. August 1999

   An LSR SHOULD adjust the resources that it reserved for a CRLSP when
   it receives a Label Mapping Message if the Traffic Parameters differ
   from those in the corresponding Label Request Message.

4.3.2.3 Notification Message

   If an LSR receives a Notification Message for a CRLSP, it SHOULD
   release any resources that it possibly had reserved for the CRLSP.
   In addition, on receiving a Notification Message from a Downstream
   LSR that is associated with a Label Request from an upstream LSR,
   the local LSR MUST propagate the Notification message using the
   procedures in [LDP]. [1].

4.4 Preemption TLV

      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

   The defualt value of the setup and holding priorities should be in
   the middle of the range (e.g., 4) so that this feature can be turned
   on gradually in an operational network by increasing or decerasing
   the priority starting at the middle of the range.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0| Preemption-TLV  (0x0820)  |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  SetPrio      | HoldPrio      |      Reserved                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

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   Type
        A fourteen-bit field carrying the value of the Preemption-TLV
        type which is 0x810.

   Length
        Specifies the length of the value field in bytes.

   Reserved
        Zero on transmission.  Ignored on receipt.

   SetPrio
        A SetupPriority of value zero (0) is the priority assigned to
        the most important path. It is referred to as the highest
        priority.  Seven (7) is the priority for the least important
        path. The higher the setup priority, the more paths CR-LDP can
        bump to set up the path. The default value should be 4.

   HoldPrio
        A HoldingPriority of value zero (0) is the priority assigned to
        the most important path. It is referred to as the highest
        priority. Seven (7) is the priority for the least important
        path.

CR-LDP Specification             - 18 -                 Exp. August 1999 The default value should be 4.
        The higher the holding priority, the less likely it is for CR-LDP CR-
        LDP to reallocate its bandwidth to a new path.

4.5 LSPID TLV

   LSPID is a unique identifier of a CRLSP within an MPLS network.
   The LSPID is composed of the ingress LSR Router ID and a Locally
   unique CRLSP ID to that LSR.

   The LSPID is useful in network management, in CR-LSP repair, and in
   using an already established CR-LSP as a hop in an ER-TLV. An action
   indicator flag_ is carried in the LSPID TLV. This _action indicator
   flag_ indicates explicitly the action that should be taken if the
   LSP already exists on the LSR receiving the message.

   The procedure for the code point _modify_ is defined in section 2.1.
   of [10]. The procedures for other flags are FFS.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|      LSPID-TLV  (0x0821)  |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Reserved        |ActFlg |      Local CRLSP ID           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Ingress LSR Router ID                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

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   Type
        A fourteen-bit field carrying the value of the  LSPID-TLV type
        which is 0x821.

   Length
        Specifies the length of the value field in bytes.

   ActFlg
        Action Indicator Flag: A 4-bit field that indicates explicitly
        the action that should be taken if the LSP already exists on
        the LSR receiving the message. A set of indicator code points
        is proposed as follows:

                0001: modify
   Reserved
        Zero on transmission.  Ignored on receipt.

   Local CRLSP ID
        The Local LSP ID is an identifier of the CRLSP locally unique
        within the Ingress LSR originating the CRLDP.

   Ingress LSR Router ID
      A 4 byte field indicating the Ingress
        "An LSR ID. may use any of its own IPv4 in this field"

4.6 Resource Class (Color) TLV

   The Resource Class as defined in [TER] [4] is used to specify which links
   are acceptable by this CRLSP. This information allows for the

CR-LDP Specification             - 19 -                 Exp. August 1999

   networks
   network's topology to be pruned.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|      ResCls-TLV  (0x0822) |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             RsCls                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

   Type
        A fourteen-bit field carrying the value of the ResCls-TLV type
        which is 0x822.

   Length
        Specifies the length of the value field in bytes.

   RsCls
        The Resource Class bit mask indicating which of the 32 "administrative groups"
        _administrative groups_ or "colors" _colors_ of links the CRLSP can
        traverse.

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4.7 ER-Hop semantics

4.7.1. ER-Hop 1: The IPv4 prefix

   The abstract node represented by this ER-Hop is the set of nodes nodes,
   which have an IP address address, which lies within this prefix.  Note that
   a prefix length of 32 indicates a single IPv4 node.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|         0x801             |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |L|      Reserved                               |    PreLen     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    IPv4 Address (4 bytes)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

CR-LDP Specification             - 20 -                 Exp. August 1999

   Type
        IPv4 Address 0x801

   Length
        Specifies the length of the value field in bytes.

   L Bit
        Set to indicate Loose hop.
        Cleared to indicate a strict hop.

   Reserved
        Zero on transmission.  Ignored on receipt.

   PreLen
        Prefix Length 1-32

   IP Address
        A four byte four-byte field indicating the IP Address.

4.7.2. ER-Hop 2: The IPv6 address

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|          0x802            |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |L|             Reserved                        |    PreLen     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  IPV6 address                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  IPV6 address (continued)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  IPV6 address (continued)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |

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   |                  IPV6 address (continued)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

   Type
        0x802  IPv6 address

   Length
        Specifies the length of the value field in bytes.

   L Bit
        Set to indicate Loose hop.

CR-LDP Specification             - 21 -                 Exp. August 1999
        Cleared to indicate a strict hop.

   Reserved
        Zero on transmission.  Ignored on receipt.

   PreLen
        Prefix Length 1-128

   IPv6 address
        A 128-bit unicast host address.

4.7.3. ER-Hop 32: 3:  The autonomous system number

   The abstract node represented by this ER-Hop is the set of nodes
   belonging to the autonomous system.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|          0x803            |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |L|          Reserved           |                AS Number      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

   Type
        AS Number 0x803

   Length
        Specifies the length of the value field in bytes.

   L Bit
        Set to indicate Loose hop.
        Cleared to indicate a strict hop.

   Reserved
        Zero on transmission.  Ignored on receipt.

   AS Number
        Autonomous System number

4.7.4. ER-Hop 4: LSPID

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   The LSPID is used to identify the tunnel ingress point as the next
   hop in the ER. This ER-Hop allows for stacking new CR-LSPs within an
   already established CR-LSP. It also allows for splicing the CR-LSP

CR-LDP Specification             - 22 -                 Exp. August 1999
   being established with an existing CR-LSP.

   If an LSPID Hop is the last ER-Hop in an ER-TLV, than the LSR may
   splice the CR-LSP of the incoming Label Request to the CR-LSP that
   currently exists with this LSPID.  This is useful, for example, at
   the point at which a Label Request used for local repair arrives at
   the next ER-Hop after the loosely specified CR-LSP segment.  Use of
   the LSPID Hop in this scenario eliminates the need for ER-Hops to
   keep the entire remaining ER-TLV at each LSR that is at either
   (upstream or downstream) end of a loosely specified CR-LSP segment
   as part of its state information. This is due to the fact that the
   upstream LSR needs only to keep the next ER-Hop and the LSPID and
   the downstream LSR needs only to keep the LSPID in order for each
   end to be able to recognize that the same LSP is being identified.

   If the LSPID Hop is not the last hop in an ER-TLV, the LSR must
   forward the remaining ER-TLV in a Label Request message, using the
   CR-LSP specified by the LSPID, to the LSR that is the CR-LSP's
   egress. That LSR will continue processing of the CR-LSP Label
   Request Message.  The result is a tunneled, or stacked, CR-LSP.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|          0x804            |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |L|          Reserved           |               Local LSPID     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Ingress LSR Router ID                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

   Type
        LSPID 0x804

   Length
        Specifies the length of the value field in bytes.

   L Bit
        Set to indicate Loose hop.
        Cleared to indicate a strict hop.

   Reserved
        Zero on transmission.  Ignored on receipt.

   Local LSPID
        A 2 byte field indicating the LSPID which is unique with
        reference to the its Ingress LSR.

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   Ingress LSR Router ID
      A 4 byte field indicating the Ingress
        "An LSR ID. may use any of its own IPv4 addresses in this field"

4.8. Processing of the Explicit Route TLV

4.8.1. Selection of the next hop

   A Label Request Message containing a explicit route TLV must
   determine the next hop for this path.  Selection of this next hop
   may involve a selection from a set of possible alternatives.  The
   mechanism for making a selection from this set is implementation
   dependent and is outside of the scope of this specification.
   Selection of particular paths is also outside of the scope of this
   specification, but it is assumed that each node will make a best
   effort attempt to determine a loop-free path.  Note that such best

CR-LDP Specification             - 23 -                 Exp. August 1999
   efforts may be overridden by local policy.

   To determine the next hop for the path, a node performs the
   following steps:

      1)

      1. The node receiving the Label Request Message must first
         evaluate the first ER-Hop. If the L bit is not set in the
         first ER-Hop and if the node is not part of the abstract node
         described by the first ER-Hop, it has received the message in
         error, and should return a "Bad _Bad initial ER-Hop" ER-Hop_ error. If the
         L bit is set and the local node is not part of the abstract
         node described by the first ER-Hop, the node selects a next
         hop that is along the path to the abstract node described by
         the first ER-Hop. If there is no first ER-Hop, the message is
         also in error and the system should return a "Bad _Bad Explicit
         Routing TLV" TLV_ error.

      2)

      2. If there is no second ER-Hop, this indicates the end of the
         explicit route. The explicit route TLV should be removed from
         the Label Request Message.  This node may or may not be the
         end of the LSP.  Processing continues with section 4.8.2,
         where a new explicit route TLV may be added to the Label
         Request Message.

      3)

      3. If the node is also a part of the abstract node described by
         the second ER-Hop, then the node deletes the first ER-Hop and
         continues processing with step 2, above.  Note that this makes
         the second ER-Hop into the first ER-Hop of the next iteration.

      4)

      4. The node determines if it is topologically adjacent to the
         abstract node described by the second ER-Hop.  If so, the node
         selects a particular next hop which is a member of the
         abstract node.  The node then deletes the first ER-Hop and
         continues processing with section 4.8.2.

      5)

Jamoussi, et. al.    draft-ietf-mpls-crldp-02.txt                   22 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

      5. Next, the node selects a next hop within the abstract node of
         the first ER-Hop that is along the path to the abstract node
         of the second ER-Hop.  If no such path exists then there are
         two cases:

      5a)

           5.a If the second ER-Hop is a strict ER-Hop, then there is
           an error and the node should return a "Bad _Bad strict node" node_
           error.

      5b)

           5.b Otherwise, if the second ER-Hop is a loose ER-Hop, then
           the node selects any next hop that is along the path to the
           next abstract node.  If no path exists within the MPLS
           domain, then there is an error, and the node should return a "Bad
           _Bad loose node" node_ error.

      6)

      6. Finally, the node replaces the first ER-Hop with any ER-Hop
         that denotes an abstract node containing the next hop.  This
         is necessary so that when the explicit route is received by
         the next hop, it will be accepted.

CR-LDP Specification             - 24 -                 Exp. August 1999

      7)

      7. Progress the Label Request Message to the next hop.

4.8.2. Adding ER-Hops to the explicit route TLV

   After selecting a next hop, the node may alter the explicit route in
   the following ways.

   If, as part of executing the algorithm in section 4.8.1, the
   explicit route TLV is removed, the node may add a new explicit route
   TLV.

   Otherwise, if the node is a member of the abstract node for the
   first ER-Hop, then a series of ER-Hops may be inserted before the
   first ER-Hop or may replace the first ER-Hop.  Each ER-Hop in this
   series must denote an abstract node that is a subset of the current
   abstract node.

   Alternately, if the first ER-Hop is a loose ER-Hop, an arbitrary
   series of ER-Hops may be inserted prior to the first ER-Hop.

4.9 Route Pinning TLV

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|          0x823            |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |P|                        Reserved                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].

   Type
        Pinning-TLV type 0x823

Jamoussi, et. al.    draft-ietf-mpls-crldp-02.txt                   23 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

   Length
        Specifies the length of the value field in bytes.

   P Bit
        The P bit is set to 1 to indicate that route pinning is
        requested.
        The P bit is set to 0 to indicate that route pinning is not
        requested

   Reserved
        Zero on transmission.  Ignored on receipt.

4.10 CRLSP FEC Element

CR-LDP Specification             - 25 -                 Exp. August 1999

   A new FEC element is introduced in this specification to support CR-
   LSPs. This new FEC element does not preclude the use of other FECs
   elements (Type=0x01, 0x02, 0x03) defined in the LDP spec in CR-LDP
   messages. The CRLDP FEC Element is an opaque FEC. FEC to be used only in
   Messages of CR-LSPs.

        FEC Element     Type    Value
      type
        Type name

        CRLSP           0x04    No value; i.e., 0 value octets;
                                            see below.

      CRLSP FEC Element
          To be used only in Messages of CR-LSPs.

   The CR-LSP FEC TLV encoding is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|
   |0|0|          FEC(0x0100)      |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | CR-LSP (4)    |          Reserved                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   U bit
      Unknown TLV bit. As defined in [LDP].

   F bit
      Forward unknown TLV bit.  As defined in [LDP].
   +-+-+-+-+-+-+-+-+

   Type
        FEC TLV type 0x0100

   Length
        Specifies the length of the value field in bytes.

   CR-LSP FEC Element Type
        0x04

   Reserved
      Zero on transmission.  Ignored on receipt.

4.11 Error subcodes

   In the processing described above, certain errors need to be
   reported as part of the Notification Message.  This section defines
   the status codes for the errors described in this specification.

CR-LDP Specification             - 26 -                 Exp. August

Jamoussi, et. al.    draft-ietf-mpls-crldp-02.txt                   24 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

         Status Code                                       Type
         --------------------------------------         ----------
         Bad Explicit Routing TLV Error                 0x04000001                 0x44000001
         Bad Strict Node Error                          0x04000002                          0x44000002
         Bad Loose  Node Error                          0x04000003                          0x44000003
         Bad Initial ER-Hop Error                       0x04000004                       0x44000004
         Resource Unavailable                           0x04000005                           0x44000005
         Traffic Parameters Unavailable                 0x04000006                 0x44000006
         Setup abort                                    0x04000007 (Label Request Aborted in [1])     0x04000015
         Modify request not supported                   0x44000008

5. Security

   Pre-emption has to be controlled by the MPLS domain.

   Resource reservation requires the LSRs to have an LSP admission
   control function.

   Normal routing can be bypassed by

   Traffic Engineered LSPs. LSPs can bypass normal routing.

6. Acknowledgments

   The messages used to signal the CRLSP setup are based on the work
   done by the [LDP] [1] team. The Explicit Route object and procedures used
   in this specification are based on [ER]. [8].

   The authors would also like to acknowledge the careful review and
   comments of Ken Hayward, Greg Wright, Geetha Brown, Brian Williams,
   Paul Beaubien, Matthew Yuen, Liam Casey, and Ankur Anand.

7. Intellectual Property Consideration

   Nortel Networks may seek patent or other intellectual property
   protection for some or all of the technologies disclosed in this
   document. If any standards arising from this document are or become
   protected by one or more patents assigned to Nortel Networks, Nortel
   Networks is prepared to make a license available to any qualified
   applicant upon reasonable and non-discriminatory terms and
   conditions. Any such licenses will be subject to negotiations
   outside of the IETF.

8. References

   [LDP]

   1  Andersson et al, "Label Distribution Protocol Specification"
      work in progress (draft-ietf-mpls-ldp-03), Feb. (draft-ietf-mpls-ldp-05), June 1999.

   [ARCH]  Rosen

   2  Callon et al, "Multiprotocol "Framework for Multiprotocol Label Switching Architecture", Switching",
      work in progress (draft-ietf-mpls-arch-04), Feb. (draft-ietf-mpls-framework-04), July 1999.

   [FRAME] Callon

   3  Rosen et al, "Framework for Multiprotocol "Multiprotocol Label Switching", Switching Architecture",
      work in progress (draft-ietf-mpls-framework-02), November
           1997.

   [TER] (draft-ietf-mpls-arch-04), April 1999.

Jamoussi, et. al.    draft-ietf-mpls-crldp-02.txt                   25 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

   4  Awduche et al, "Requirements for Traffic Engineering Over
      MPLS", work in progress (draft-ietf-mpls-traffic-eng-00),
           August 1998.

   [ER]    Guerin et al, "Setting up Reservations on Explicit Paths
           using RSVP", work in progress (draft-guerin-expl-path-rsvp-
   01)
           November 1997.

CR-LDP Specification             - 27 -                 Exp. August 1999

   [VPN1] (draft-ietf-mpls-traffic-eng-01),
      June 1999.

   5  Heinanen et al, "MPLS Mappings of Generic VPN Mechanisms",
      work in progress (draft-heinanen-generic-vpn-mpls-00),
      August 1998.

   [VPN2]

   6  Jamieson et al, "MPLS VPN Architecture" work in progress
     (draft-jamieson-mpls-vpn-00), August 1998.

   [VPN3]

   7  T. Li, "CPE based VPNs using MPLS", work in progress (draft-
      li-mpls-vpn-00.txt), October 1998.

   [LDP-STATE]

   8  Guerin et al, "Setting up Reservations on Explicit Paths using
      RSVP", work in progress (draft-guerin-expl-path-rsvp-01) November
      1997.

   9  L. Wu, et. al., "LDP State Machine" work in progress
      (draft-ietf-mpls-ldp-state-00), Feb 1999.

CR-LDP Specification             - 28 -                 Exp. August 1999

8. Author Information

   10 J. Ash, et. al., _LSP Modification Using CR-LDP_ work in progress
      (draft-ash-crlsp-modify-00.txt), July 1999.

9. Author's Addresses

   Osama S. Aboul-Magd               Loa Andersson
   Nortel Networks                           Director Bay Architecture Lab,EMEA                   Nortel Networks
   P O Box 3511 Station C            Kungsgatan 34, PO Box 1788
   Ottawa, ON K1Y 4H7                111 97 Stockholm, Sweden
   Canada                                    phone:                            Phone: +46 8 441 78 34
phone:
   Phone: +1 613 763-5827                    mobile            Mobile +46 70 522 78 34
osama@NortelNetworks.com                  loa_andersson@baynetworks.com
   Osama@nortelnetworks.com          Loa_andersson@beynetworks.com

   Peter Ashwood-Smith               Ross Callon
   Nortel Networks                   IronBridge Networks
   P O Box 3511 Station C            55 Hayden Avenue,
   Ottawa, ON K1Y 4H7                Lexington, MA  02173
   Canada                            Phone: +1-781-402-8017
phone:
   Phone: +1 613 763-4534                    rcallon@ironbridgenetworks.com
petera@NortelNetworks.com            Rcallon@ironbridgenetworks.com
   Petera@nortelnetworks.com

   Ram Dantu                         Paul Doolan
   Alcatel USA Inc.                  Ennovate Networks
   IP Competence Center              330 Codman Hill Rd
   1201 E. Campbell Road.,446-315    Marlborough MA 01719
   Richadson, TX USA., 75081-2206    Phone: 978-263-2002
   Phone: 972 996 2938                       pdoolan@ennovatenetworks.com               Pdoolan@ennovatenetworks.com
   Fax:   972 996 5902
ram.dantu@aud.alcatel.com
   Ram.dantu@aud.alcatel.com

Jamoussi, et. al.    draft-ietf-mpls-crldp-02.txt                   26 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

   Nancy Feldman                     Andre Fredette
   IBM Corp.                         Nortel Networks
   17 Skyline Drive                  3 Federal Street
   Hawthorne NY 10532                Billerica, MA 01821
   Phone:  914-784-3254                      fredette@baynetworks.com
nkf@us.ibm.com              978-288-8524
   Nkf@us.ibm.com                    Fredette@baynetworks.com

   Eric Gray                         Joel M. Halpern
   Lucent Technologies, Inc                  Newbridge Networks Inc.          Institutional Venture Partners
   1600 Osgood St.                           593 Herndon Parkway                   650-926-5633
   North Andover, MA  01847                  Herndon, VA 20170          joel@mcquillan.com
   Phone: 603-659-3386                       phone: 1-703-736-5954
ewgray@lucent.com                         jhalpern@newbridge.com
   Ewgray@lucent.com

   Juha Heinanen                     Fiffi Hellstrand
   Telia Finland, Inc.               Ericsson Telecom AB
   Myyrmaentie 2                     S-126 25 STOCKHOLM
   01600 VANTAA                      Sweden
   Finland                           Tel: +46 8 719 4933
   Tel: +358 41 500 4808             etxfiff@etxb.ericsson.se
jh@telia.fi

CR-LDP Specification             - 29 -                 Exp. August 1999
   Jh@telia.fi

   Bilel Jamoussi                    Timothy E. Kilty
   Nortel Networks Corp.             Northchurch Communications
P O Box 3511 Station C
   3 Federal Street                  5 Corporate Drive,
Ottawa, ON K1Y 4H7
   Billerica, MA 01821               Andover, MA 018110
Canada
   USA                               phone: 978 691-4656
phone:
   Phone: +1 613 765-4814 978 288-4506            tkilty@northc.com
jamoussi@NortelNetworks.com
   Jamoussi@nortelnetworks.com

   Andrew G. Malis                   Muckai K Girish
   Ascend Communications, Inc.       SBC Technology Resources, Inc.
   1 Robbins Road                    4698 Willow Road
   Westford, MA 01886                Pleasanton, CA 94588
phone:
   Phone: 978 952-7414               Phone: (925) 598-1263
   fax:   978 392-2074               Fax:   (925) 598-1321
malis@ascend.com
   Malis@ascend.com                  mgirish@tri.sbc.com

   Kenneth Sundell                   Pasi Vaananen
Ericsson
   Nortel Networks                   Nokia Telecommunications
SE-126 25 Stockholm
   Architecture Lab, EMEA            3 Burlington Woods Drive, Suite 250
Sweden
   Kungsgatan 34, PO Box 1788        Burlington, MA 01803
kenneth.sundell@etx.ericsson.se
   111 97 Stockholm, Sweden          Phone: +1-781-238-4981
                                          pasi.vaananen@ntc.nokia.com
   phone: +46 8 441-7838,            Pasi.vaananen@ntc.nokia.com
   mobile +46 70 665-7838
   ksundell@nortelnetworks.com

Jamoussi, et. al.   draft-ietf-mpls-cr-ldp-02.txt                   27 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

   Tom Worster worster                       Liwen Wu
General DataComm, Inc.
   Nokia                             Alcatel U.S.A
5 Mount Royal Ave.
   3 Burlington Woods Dr.            44983 Knoll Square
Marlboro MA 01752
   Suite 250                         Ashburn, Va. 20147
tom.worster@gdc.com
   Burlington MA 01803 USA           Phone: (703) 724-2619
   +1 617 247 2624                   FAX:   (703) 724-2005
                                          liwen.wu@adn.alcatel.com

CR-LDP Specification             - 30 -                 Exp. August
   tom.worster@nokia.com             Liwen.wu@and.alcatel.com

Jamoussi, et. al.   draft-ietf-mpls-cr-ldp-02.txt                   28 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

Appendix A: CRLSP Establishment Examples

A.1 Strict Explicit Route Example

   This appendix provides an example for the setup of a strictly routed
   CRLSP.  In this example,  each  abstract  node  is represented by a specific node represents each abstract
   node.

   The sample network used here is a four node  network  with  two
   edge LSRs and two core LSRs as follows:

                             a         b         c

   abc
   LSR1------LSR2------LSR3------LSR4

   LSR1 generates a Label Request Message as described in Section 3.1
   of this draft and sends it to LSR2. This message includes the CR-TLV.

   The ER-TLV is composed by a CR-
   TLV.

   A vector of three ER-Hop TLVs <a, b, c>. c> composes the ER-TLV.
   The ER-Hop TLVs used in this example are of type 0x0801 (IPv4
   prefix) with a prefix length of 32. Hence, each ER-Hop TLV
   identifies a specific node as opposed to a group of nodes.
   At LSR2, the following processing of the ER-TLV per Section 4.8.1 of
   this draft takes place:

        1) The first hop <a> is part of the abstract node LSR2.
           Therefore, the first step passes the test. Go to step 2.

        2) There is a second ER-Hop, <b>. Go to step 3.

        3) LSR2 is not part of the abstract node described by the
        second ER-Hop <b>. Go to Step 4.

        4) LSR2 determines that it is topologically adjacent to the
        abstract node described by the second ER-Hop <b>. LSR2 selects
        a next hop (LSR3) which is the abstract node. LSR2 deletes the
        first ER-Hop <a> from the ER-TLV which now becomes <b , c>. Go
        to Section 4.8.2.

   At LSR2, the following processing of Section 4.8.2 takes place:
   Executing algorithm 4.8.1 did not result in the removal of the
      ER-TLV. ER-
   TLV.

   Also, LSR2 is not a member of the abstract node described by the
   first ER-Hop <b>.

   Finally, the first ER-Hop <b> is a strict hop.

   Therefore, processing section 4.8.2 does not result in the insertion
   of new ER-Hops. The selection of the next hop has been

CR-LDP Specification             - 31 -                 Exp. August 1999 already done
   is step 4 of Section 4.8.1 and the processing of the ER-TLV is

Jamoussi, et. al.   draft-ietf-mpls-cr-ldp-02.txt                   29 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

   completed at LSR2. In this case, the Label Request Message including
   the ER-TLV <b, c> is progressed by LSR2 to LSR3.

   At LSR3, a similar processing to the ER-TLV takes place except that
   the incoming ER-TLV = <b, c> and the outgoing ER-TLV is <c>.

   At LSR4, the following processing of section 4.8.1 takes place:

        1) The first hop <c> is part of the abstract node LSR4.
           Therefore, the first step passes the test. Go to step 2.

        2) There is no second ER-Hop, this indicates the end of the
        CRLSP. The ER-TLV is removed from the Label Request Message.
        Processing continues with Section 4.8.2.

   At LSR4, the following processing of Section 4.8.2 takes place:
   Executing algorithm 4.8.1 resulted in the removal of the ER-TLV.
   LSR4 does not add a new ER-TLV.

   Therefore, processing section 4.8.2 does not result in the insertion
   of new ER-Hops. This indicates the end of the CRLSP and the
   processing of the ER-TLV is completed at LSR4.

   At LSR4, processing of Section 3.2 is invoked. The first condition
   is satisfied (LSR4 is the egress end of the CRLSP and upstream
   mapping has been requested). Therefore, a Label Mapping Message is
   generated by LSR4 and sent to LSR3.

   At LSR3, the processing of Section 3.2 is invoked. The second
   condition is satisfied (LSR3 received a mapping from its downstream
   next hop LSR4 for a CRLSP for which an upstream request is still
   pending). Therefore, a Label Mapping Message is generated by LSR3
   and sent to LSR2.

   At LSR2, a similar processing to LSR 3 takes place and a Label
   Mapping Message is sent back to LSR1 which completes the end-to-end
   CRLSP setup.

A.2. Node Groups and Specific Nodes Example

   A request at an ingress LSR to setup a CRLSP might originate from a
   management system or an application, the details are implementation
   specific.

   The ingress LSR uses information provided by the management system
   or the application and possibly also information from the routing
   database to calculated calculate the explicit route and to create the Label
   Request Message.

CR-LDP Specification             - 32 -                 Exp. August 1999

   The Label request message carries together with other necessary
   information a ER-TLV defining the explicitly routed path. In our
   example the list of hops in the ER-Hop TLV is supposed to contain an

Jamoussi, et. al.   draft-ietf-mpls-cr-ldp-02.txt                   30 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

   abstract node representing a group of nodes, an abstract node
   representing a specific node, another abstract node representing a
   group of nodes, and an abstract node representing a specific egress
   point.

   In--{Group 1}--{Specific A}--{Group 2}--{Specific Out: B}
   The ER-TLV contains four ER-Hop TLVs:

        1. An ER-Hop TLV that specifies a group of LSR valid for the
           first abstract node representing a group of nodes (Group 1).

        2. An ER-Hop TLV that indicates the specific node (Node A).

        3. An ER-Hop TLV that specifies a group of LSRs valid for the
           second abstract node representing a group of nodes (Group
           2).

        4. An ER-Hop TLV that indicates the specific egress point for
           the CRLSP (Node B).

   All the ER-Hop TLVs are strictly routed nodes.
   The setup procedure for this CRLSP works as follows:

        1. The ingress node sends the Label Request Message to a node
           that is a member the group of nodes indicated in the first
           ER-Hop TLV, following normal routing for the specific node
           (A).

        2. The node that receives the message identifies itself as part
           of the group indicated in the first ER-Hop TLV, and that it
           is not the specific node (A) in the second. Further it
           realizes that the specific node (A) is not one of its next
           hops.

        3. It keeps the ER-Hop TLVs intact and sends a Label Request
           Message to a node that is part of the group indicated in the
           first ER-Hop TLV (Group 1), following normal routing for the
           specific node (A).

        4. The node that receives the message identifies itself as part
           of the group indicated in the first ER-Hop TLV, and that it
           is not the specific node (A) in the second ER-Hop TLV.
           Further it realizes that the specific node (A) is one of its
           next hops.

        5. It removes the first ER-Hop TLVs and sends a Label Request
           Message to the specific node (A).

        6. The specific node (A) recognizes itself in the first ER-Hop
           TLV. Removes the specific ER-Hop TLV.

CR-LDP Specification             - 33 -                 Exp. August

Jamoussi, et. al.   draft-ietf-mpls-cr-ldp-02.txt                   31 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

        7. It sends a Label Request Message to a node that is a member
           of the group (Group 2) indicated in the ER-Hop TLV.

        8. The node that receives the message identifies itself as part
           of the group indicated in the first ER-Hop TLV, further it
           realizes that the specific egress node (B) is one of its
           next hops.

        9. It sends a Label Request Message to the specific egress node
           (B).

      10. The

        10.The specific egress node (B) recognizes itself as the egress

           for the CRLSP, it returns a Label Mapping Message, that will
           traverse the same path as the Label Request Message in the
           opposite direction.

CR-LDP Specification             - 34 -                 Exp. August

Jamoussi, et. al.   draft-ietf-mpls-cr-ldp-02.txt                   32 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

                    Appendix B. QoS Service Examples

B.1 Service Examples

   Construction of an end-to-end service is the result of the rules
   enforced at the edge and the treatment that packets receive at the
   network nodes. The rules define the traffic conditioning actions
   that are implemented at the edge and they include policing with
   pass, mark, and drop capabilities. The edge rules are expected to
   be defined  by  the  mutual agreements between the service providers
   and their customers and they will constitute an  essential  part  of
   the SLA. Therefore edge rules are not included in the signaling
   protocol.

   Packets

   Packet treatment at a network node is usually referred to as the
   local behavior.  Local behavior could be specified in many ways. One
   example for local behavior specification is the service frequency
   introduced in section   4.3.2.1., 4.3.2.1, together with the resource
   reservation rules implemented at the nodes.

   Edge rules and local behaviors can be viewed as the main building
   blocks for the end-to-end service construction. The following table
   illustrates the applicability of the building block approach for
   constructing different services including those defined for ATM.

   Service        PDR  PBS  CDR     CBS   EBS  Service    Conditioning
   Examples                                    Frequency  Action
---------------------------------------------------------------------------

   DS             S    S    =PDR    =PBS  0    Frequent   drop>PDR

   TS             S    S    S       S     0    Unspecified drop>PDR,PBS
                                                           mark>CDR,CBS

   BE             inf  inf  inf     inf   0    Unspecified      -

   FRS            S    S    CIR     ~B_C  ~B_E Unspecified drop>PDR,PBS
                                                       mark>CDR,CBS,EBS

   ATM-CBR        PCR  CDVT =PCR    =CDVT 0    VeryFrequent    drop>PCR

   ATM-VBR.3(rt)  PCR  CDVT SCR     MBS   0    Frequent        drop>PCR
                                                           mark>SCR,MBS

   ATM-VBR.3(nrt) PCR  CDVT SCR     MBS   0    Unspecified     drop>PCR
                                                           mark>SCR,MBS

   ATM-UBR        PCR  CDVT -       -     0    Unspecified     drop>PCR

   ATM-GFR.1      PCR  CDVT MCR     MBS   0    Unspecified     drop>PCR

CR-LDP Specification             - 35 -                 Exp. August 1999

   ATM-GFR.2      PCR  CDVT MCR     MBS   0    Unspecified     drop>PCR
                                                           mark>MCR,MFS

Jamoussi, et. al.   draft-ietf-mpls-cr-ldp-02.txt                   33 Internet Draft   Constraint-Based LSP Setup using LDP     August, 1999

   int-serv-CL    p    m    r       b     0    Frequent        drop>p
                                                               drop>r,b

   S= User specified

   In the above table, the DS refers to a delay sensitive service where
   the network commits to deliver with high probability user datagrams
   at a rate of PDR with minimum delay and delay requirements.
   Datagrams in excess of PDR will be discarded.

   The TS refers to a generic throughput sensitive service where the
   network commit commits to deliver with high probability user datagrams at a
   rate of at least CDR. The user may transmit at a rate higher than
   CDR but datagrams in excess of CDR would have a lower probability of
   being delivered.

   The BE is the best effort service and it implies that there are no
   expected service guarantees from the network.

B.2. Establishing CR-LSP Supporting Real-Time Applications

   In this scenario the customer needs to establish an LSP for
   supporting real-time applications such voice and video. The Delay-
   sensitive (DS) service is requested in this case.

   The first step is the specification of the traffic parameters in the
   signaling message. The two parameters of interest to the DS service
   are the PDR and the PBS and their values are specified by the user based on his requirements. requirements
   specifies their values. Since all the traffic parameters are
   included in the signaling message, appropriate values must be
   assigned to all of them. For DS service, the CDR and the CBS values
   are set equal to the PDR and the PBS respectively. An indication of
   whether the parameter values are subject to negotiation is flagged.

   The transport characteristics of the DS service requires require that
   Frequent frequency to be requested to reflect the real-time delay
   requirements of the service.

   In addition to the transport characteristics, both the network
   provider and the customer need to agree on the actions enforced at
   the edge. The specification of those actions is expected to be a
   part of the service level agreement (SLA) negotiation and is not
   included in the signaling protocol. For DS service, the edge action
   is to drop packets that exceed the PDR and the PBS specifications.
   The signaling message will be sent in the direction of the ER path
   and the LSP is established following the normal LDP procedures. Each

CR-LDP Specification             - 36 -                 Exp. August 1999
   LSR applies its admission control rules. If sufficient resources are
   not available and the parameter values are subject to negotiation,
   then the LSR could negotiate down either the PDR, the PBS, or both.

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   The new parameters parameter values are echoed back in the Label Mapping
   Message. LSRs might need to re-adjust their resource reservations
   based on the new traffic parameter values.

B.3. Establishing CR-LSP Supporting Delay Insensitive Applications

   In this example we assume that a throughput sensitive (TS) service
   is requested. For resource allocation the user assigns values for
   PDR, PBS, CDR, and CBS. The negotiation flag is set if the traffic
   parameters are subject to negotiation.
   Since the service is delay insensitive by definition, the
   Unspecified frequency is signaled to indicate that the service
   frequency is not an issue.

   Similar to the previous example, the edge actions are not subject
   for signaling and are specified in the service level agreement
   between the user and the network provider.

   For TS service, the edge rules might include marking to indicate
   high discard precedence values for all packets that exceed CDR and
   the CBS. The edge rules will also include dropping of packets that
   are do not conform to either neither PDR and nor PBS.

   Each LSR of the LSP is expected to run its admission control rules
   and negotiate traffic parameters down if sufficient resources do not
   exist. The new parameters parameter values are echoed back in the Label Mapping
   Message. LSRs might need to re-adjust their resources based on the
   new traffic parameter values.

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