MPLS Working Group              L. Andersson, A. Fredette, B. Jamoussi                             Bilel Jamoussi, Editor
Internet Draft                                        Nortel Networks
Expiration Date: July August 1999

                                                        February 1999
                                                             R. Callon
                                                   IronBridge Networks

                                                             P. Doolan
                                                     Ennovate Networks

                                                            N. Feldman
                                                              IBM Corp

                                                               E. Gray
                                                   Lucent Technologies

                                                            J. Halpern
                                                    Newbridge Networks

                                                           J. Heinanen
                                                         Telia Finland

                                                           T. E. Kilty
                                            Northchurch Communications

                                                           A. G. Malis
                                           Ascend Communications, Inc.

                                                             M. Girish
                                        SBC Technology Resources, Inc.

                                                            K. Sundell
                                                              Ericsson

                                                           P. Vaananen
                                              Nokia Telecommunications

                                                            T. Worster
                                                General DataComm, Inc.

                                                       L. Wu, R. Dantu
                                                               Alcatel

                                                          January 1998

                  Constraint-Based LSP Setup using LDP

                     draft-ietf-mpls-cr-ldp-00.txt

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

Status of this Memo

   This document is an Internet-Draft. Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working

CR-LDP Specification             - 2 -                     Exp. Apr 1999 documents of the Internet Engineering
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   Distribution of this memo is unlimited.

Copyright Notice

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

Abstract

   Label Distribution Protocol (LDP) is defined in [LDP] 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 an explicit route constraint, a Service Class (SC)
   constraint, or both. constraints, QoS constraints, and
   others. Constraint-based routing (CR) and is a mechanism used to meet
   Traffic Engineering requirements that have been proposed by [FRAME],
   [ARCH] and [TER]. 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] ([VPN1], [VPN2] and [VPN2]). [VPN3]).

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

Table of Contents

   1.         Introduction

   The need for constraint-based routing (CR) in MPLS has been explored
   elsewhere [ARCH], [FRAME], .........................................   3
   2.         Constraint-based Routing Overview ....................   3
   2.1        Strict and [TER]. Loose Explicit routing is a subset
   of the more general constraint-based routing function. At the MPLS WG
   meeting held during the Washington IETF there was consensus that LDP
   should support explicit routing of LSPs with provision for indication
   of associated (forwarding) priority.  In the Chicago meeting, the
   decision was made that support for explicit path setup in LDP will be
   moved to a separate document. This document provides that support. We
   propose 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 for the explicitly
   routed LSP.

   We introduce TLVs and procedures that provide support for:

CR-LDP Specification             - 3 -                     Exp. Apr 1999

    - Strict and Loose Explicit Routing
    - Specification of Service Class
    - Specification of Routes .....................   4
   2.2        Traffic Parameters
    - Characteristics ..............................   4
   2.3        Pre-emption ..........................................   5
   2.4        Route Pinning
    - CRLSP bumping though setup/holding priority
    - Handling Failures

2. CRLSP Overview

   CRLSP over LDP Specification is designed with several goals in mind:

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

      2. Build on already specified functionality that meets the
      requirements whenever possible. Hence, this specifications is
      based on [LDP] and the Explicit Route object and procedures
      defined in [ER]. ........................................   5
   2.5        Resource Class .......................................   5
   3. Keep the solution simple         Solution Overview ....................................   5
   3.1        Required Messages and tractable.

   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 explicitly routed LSPs in this specification depends on
   the following minimal LDP behaviors as specified in [LDP]:

      - Basic and/or Extended Discovery Mechanisms.

      - Use the TLVs ...........................   7
   3.2        Label Request Message defined in [LDP] in downstream on
      demand label advertisement mode with ordered control.

      - Use the ................................   7
   3.3        Label Mapping Message defined in [LDP] in downstream on
      demand mode with ordered control.

      - Use the ................................   8
   3.4        Notification Message defined in [LDP].

      - Use the Withdraw and .................................   9
   3.5        Release & Withdraw Messages defined in [LDP].

      - Loop detection (in the case of loosely routed segments of a
      CRLSP) mechanisms.

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

      - The Label Request Message used to setup a CRLSP includes a CR- ..........................   9
   4.         Protocol Specification  ..............................   9
   4.1        Explicit Route TLV based on the path vector defined in [ER] and specified in
      Section 4 of this document.

CR-LDP Specification             - 4 -                     Exp. Apr 1999

      - An LSR implicitly infers ordered control from the existence of a
      CR-TLV in the (ER-TLV)  .........................  10
   4.2        Explicit Route Hop TLV  ..............................  10
   4.3        Traffic Parameters TLV  ..............................  12
   4.3.1      Semantics  ...........................................  13
   4.3.1.1    Frequency  ...........................................  13
   4.3.1.2    Peak Rate  ...........................................  14
   4.3.1.3    Committed Rate  ......................................  14
   4.3.1.4    Excess Burst Size ....................................  14
   4.3.1.5    Peak Rate Token Bucket................................  14
   4.3.1.6    Committed Data Rate Token Bucket .....................  15
   4.3.1.7    Weight ......................... .....................  16
   4.3.2      Procedures ...........................................  16
   4.3.2.1    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 Message ................................  16
   4.3.2.2    Label Request Mapping Message includes a CR TLV, then ordered control is used to setup
      the CRLSP. Note that this is also true for ................................  16
   4.3.2.3    Notification Message .................................  17
   4.4        Preemption TLV .......................................  18
   4.5        LSPID TLV  ...........................................  18
   4.6        Resource Class TLV  ..................................  19
   4.7        ER-Hop Semantics .....................................  19
   4.7.1      ER-Hop 1 TLV IPv4 Prefix .............................  20
   4.7.2      ER-Hop 2 TLV IPv6 Prefix .............................  20
   4.7.3      ER-Hop 3 TLV AS Number ...............................  21
   4.7.4      ER-Hop 4 TLV LSPID ...................................  21
   4.8        Processing of the loosely routed
      parts ER-TLV .............................  22
   4.8.1      Selection of a CRLSP.

      - Traffic Parameters TLVs may optionally be carried in the next hop ............................  22
   4.8.2      Adding the Label Request Message to specify the CRLSP traffic characteristics. next hop .....  24
   4.9        Route Pinning TLV  ...................................  24
   4.10       CR-LSP FEC Element ...................................  24
   4.11       Error Subcodes  ......................................  25

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

   Examples of CRLSP establishment are given in 3 -                  Exp. August 1999

   5.         Security Considerations ..............................  26
   6.         Acknowledgement ......................................  26
   7.         References ...........................................  26
   8.         Author Information ...................................  28

   Appendix A to illustrate
   how the mechanisms described in this draft work.

3. Required Messages and TLVs

   Any Messages, TLVs, CRLSP Establishment Examples .........................  30
   A.1        Strict Explicit Route Example ........................  30
   A.2        Node Groups and procedures not defined explicitly in this
   document are defined in the [LDP] Specification. Specific Nodes Example ...............  31

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

1. Introduction

   The following
   subsections are meant as a cross reference to the [LDP] document and
   indication of additional functionality beyond what's defined need for constraint-based routing (CR) in [LDP]
   where necessary.

3.1 Label Request Message

   The Label Request Message MPLS has been explored
   elsewhere [ARCH], [FRAME], and [TER].  Explicit routing is as defined in 3.5.8 a subset
   of [LDP] with the
   following modifications (required only if the CR-TLV is included in the Label Request Message):

      - Only a single FEC-TLV may be included in more general constraint-based routing function. At the Label Request
      Message.

      - The Optional Parameters TLV includes MPLS WG
   meeting held during the definition Washington IETF there was consensus that LDP
   should support explicit routing of LSPs with provision for indication
   of associated (forwarding) priority.  In the
      Constraint-based TLV specified Chicago meeting, a
   decision was made that support for explicit path setup in Section 4 LDP will be
   moved to a separate document. This document provides that support and the Traffic
      Parameters TLV specified
   it has been accepted as a working document in Section 5.

      - The Procedures to handle the Label Request are augmented Orlando meeting.
   This specification proposes an end-to-end setup mechanism of a
   constraint-based routed LSP (CRLSP) initiated by the
      procedures ingress LSR. We
   also specify mechanisms to provide means for processing reservation of the CR-TLV as defined in Section 4.

      - The Procedures to handle Service Classes are 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
      5.

3.2 Label Mapping Message

   The Label Mapping Message 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 as a mechanism that supports the Traffic
   Engineering requirements defined in 3.5.7 [TER]. Explicit Routing is a
   subset of [LDP] with the
   following modifications:

      - Only a single Label-TLV may be included in more general constraint-based routing where the Label Mapping
      Message.

CR-LDP Specification             - 5 4 -                  Exp. Apr August 1999

      - The FEC-Label Mapping TLV does not include any of

   constraint is the optional
      TLVs.

      - The Label Mapping Message Procedures explicit route (ER). Other constraints are limited defined
   to downstream
      on demand ordered provide a network operator with control mode of mapping.

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

      1. The LSR
   LSP. This section is the egress end an overview of the CRLSP various constraints supported
   by this specification.

2.1 Strict and an upstream mapping
      has been requested.

      2. The LSR received a mapping from its downstream next hop LSR for Loose Explicit Routes

   Like any other LSP an CRLSP for which an upstream request is still pending.

3.3. Notification Message a path through an MPLS network. The Notification message
   difference is as defined in Section 3.5.1 of [LDP] and
   the Status TLV encoding is as defined in Section 3.4.7 of [LDP].

   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 that while other paths are defined setup solely based on
   information in Section 4.8.3 to signal
   error notifications associated with the establishment of routing tables or from a CRLSP and
   the processing of management system, the CR-TLV.

4. Constraint-based Routing TLV

   Label Request Messages defined in [LDP] optionally carry
   constraint-based route is calculated at one point at the
   Constraint-based Routing TLV (CR-TLV) 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 path vector
   defined in [ER] and described LSP in this section of order to better support
   the specification. traffic sent over the LSP. The inclusion of reason for setting up CRLSPs,
   might be that one wants to assign certain bandwidth or other Service
   Class characteristics to the CR TLV in 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 indicates  as a
   list of nodes or groups of nodes along the path to be taken in constraint-based route.
   When the network even if normal routing indicates
   otherwise.

   The format CRLSP is established, all or a subset of the CR-TLV is described below.

4.1 CR-TLV

   The CR-TLV is an object that specifies nodes in a
   group may be traversed by the path LSP.  Certain operations to be taken by
   performed along the
   LSP being established. In addition, the CR-TLV may path can also include 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 Service Class (SC) constraints associated with CRLSP, allows the LSP,
   system a setup
   and significant amount of local flexibility in fulfilling a holding priority used
   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 bumping, and including all of the identified groups of nodes.

   To simplify the discussion, we call each group of nodes an LSP pinning
   request flag.  Reserved bits in abstract
   node.  Thus, we can also say that a constraint-based route is a path
   including all of the CR-TLV allow for abstract nodes, with the
   specification specified operations
   occurring along that path.

2.2 Traffic Characteristics

   The traffic characteristics of other LSP attributes a path are described in the future. If Traffic
   Parameters TLV in terms of a peak rate, committed rate, and service
   granularity. The peak and committed rates describe the reserved
   bits are exhausted, additional TLVs may bandwidth
   constraints of a path while the service granularity can be specified used to allow for
   specify a constraint on the
   indication of other LSP attributes during delay variation that the CRLSP setup. CRLDP MPLS
   domain may introduce to a path's traffic.

CR-LDP Specification             - 6 5 -                  Exp. Apr 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|         CR-TLV  (0x0800)  |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Reserved              | Reserved  |  SC |P| Hp  | Sp  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          ER-Hop TLV 1                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          ER-Hop TLV 2                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                          ............                         ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          ER-Hop TLV n                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

U bit

   Unknown TLV bit.  Upon receipt

2.3 Pre-emption

   CR-LDP signals the resources required by a path on each hop of an unknown TLV, if clear (=0), the
   route. If a
   notification must route with sufficient resources can not be returned to the message originator and the
   entire message must found,
   existing paths may be ignored; if set (=1), rerouted to reallocate resources to the unknown TLV new
   path. This is
   silently ignored and the rest process of the message is processed as if the
   unknown TLV did not exist.

F bit

   Forward unknown TLV bit.  This bit only applies when the U bit is set path pre-emption. Setup and the LDP message containing the unknown TLV is holding
   priorities are used to be forwarded.
   If clear (=0), the unknown TLV is not forwarded with rank existing paths (holding priority) and the containing
   message;
   new path (setup priority) to determine if set (=1), the unknown TLV is forwarded with the
   containing message.

Type

   A two byte field carrying new path can pre-empt
   an existing path.

   The setupPriority of a new CRLSP and the value holdingPriority attributes
   of the CR-TLV type which is
   0x800.

Length

   Specifies existing CRLSP are used to specify priorities. Signaling a
   higher holding priority expresses that the length path, once it has been
   established, should have a lower chance of being pre-empted.
   Signaling a higher setup priority expresses the value field expectation that, in bytes.

Reserved

   This field
   the case that resource are unavailable, the path is reserved.  It must be set to zero on transmission and
   must be ignored on receipt. We expect more likely to use these fields for
   carrying information that support
   pre-empt other constrain-based routing
   information.

P bit

CR-LDP Specification             - 7 -                     Exp. Apr 1999

   When set indicates that the loosely routed segments must remain
   pinned-down.  CRLSP must be rerouted only when adjacency is lost
   along the segment.  When not set, it indicates that the loose segment
   is not pinned down and must be changed to match the underlying hop-
   by-hop path.

SC paths. The SC Field is used to specify the Service Class exact rules determining bumping are an
   aspect of the CRLSP. This
   field allows for the definition network policy.

   The allocation of up to 8 different Service Classes.
   Currently, Three Service Classes are defined: Best Effort (0),
   Throughput Sensitive (1), setup and Delay Sensitive (2) Service Classes.
   These SCs are further defined in Section 5.

Sp

   A SetupPriority of value zero (0) is the holding priority assigned to the
   most important path. It is referred values to as the highest priority. Four
   (4) paths is the priority for the least important path. an
   aspect of network policy.

   The higher the setup priority, the more paths CR-LDP can bump and holding priority values range from zero (0) to set up the path. seven
   (7). The default value is 2. Values 5, 6, and 7 are reserved.

Hp

   A HoldingPriority of value zero (0) is the priority assigned to the most
   important path. It is referred to as the highest priority. Four
   (4) Seven (7)
   is the priority for the least important path. The higher the
   holding priority, the less likely it is for CR-LDP to reallocate its
   bandwidth to a new path.  The use of default value
   priority values is 2. Values 5, 6, and 7
   are reserved.

4.1.1 Setup and holding priorities

   CR-LDP signals the resources required by a path on each hop an aspect of network policy.

   The setupPriority of the
   route. If a route with sufficient resources can CRLSP should not be found,
   existing paths may higher (numerically less)
   than its holdingPriority since it might bump an LSP and be rerouted to reallocate resources to the new
   path. This bumped by
   next "equivalent" request.

2.4 Route Pinning

   Route pinning is the process of bumping paths. Setup and holding
   priorities are used to rank existing paths (holding priority) and the
   new path (setup priority) applicable to determine if the new path can bump an
   existing path.

   The setupPriority segments of an LSP that are loosely
   routed - i.e. those segments which are specified with a new CRLSP and next hop with
   the holdingPriority attributes
   of 'L' bit set or where the existing next hop is an "abstract node".  A CRLSP are used to specify these priorities. The
   higher the holding priority, the less likely
   may be setup using route pinning if it is for CR-LDP to
   reallocate its bandwidth undesirable to a new path. Similarly, the higher the
   setup priority, change the more paths CR-LDP can bump to set up
   path used by an LSP because a better next hop becomes available at
   some LSR along the path.

   The setup and holding priority values range from zero (0) to four
   (4). The value zero (0) is loosely routed portion of the priority assigned to LSP.

2.5 Resource Class

   Network resources may be classified in various ways by the most
   important path. It network
   operator. These classes are also known as "colors" or "administrative
   groups". When an CR-LSP is referred being established, it's necessary to as
   indicate which resource classes the highest priority. Four (4) CR-LSP can draw from.

3. Solution Overview

   CRLSP over LDP Specification is designed with the priority for the least important path. The default values for following goals:

CR-LDP Specification             - 8 6 -                  Exp. Apr August 1999

   both setup and holding priority should be 2. By setting

      1. Meet the default
   value of both setup requirements outlined in [TER] for performing traffic
      engineering and holding priorities at the middle of the
   range, all connections are initially treated the same. However, when
   network operators see provide a need solid foundation for performing more
      general constraint-based routing.

      2. Build on already specified functionality that meets the use of path bumping, the values
   of setup
      requirements whenever possible. Hence, this specifications is
      based on [LDP] and holding priorities can be gracefully adjusted up or down
   from the middle of the range.

   An existing path can be bumped if Explicit Route object and only if the setupPriority of procedures
      defined in [ER].

      3. Keep the new path solution simple.

   In this document, support for unidirectional point-to-point CRLSPs is numerically less than
   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 holdingPriority of following minimal LDP behaviors as specified in [LDP]:

      - Basic and/or Extended Discovery Mechanisms.

      - Use the
   existing path.

   To illustrate Label Request Message defined in [LDP] in downstream on
      demand label advertisement mode with ordered control.

      - Use the use of Label Mapping Message defined in [LDP] in downstream on
      demand mode with ordered control.

      - Use the setup and holding priority, consider a
   network which supports two service types (e.g., video and data
   services).  The video traffic is given a low setup priority because
   new video paths can use an alternate public network if Notification Message defined in [LDP].

      - Use the primary
   network cannot accommodate Withdraw and Release Messages defined in [LDP].

      - Use the new path. However, Loop Detection (in the video traffic
   is given case of loosely routed segments
      of a high holding priority since it is undesirable for CRLSP) mechanisms defined in [LDP].

   In addition, the path following functionality is added to be rerouted during an active LSP. For data traffic, high setup and
   holding priorities are desirable since data paths cannot be
   established on an alternate network. what's defined
   in [LDP]:

      - The setup and holding priorities can be different Label Request Message used to allow setup at a CRLSP includes one priority and holding at an independent priority. This would allow
   some calls not to invoke bumping and not to be bumped at or
      more CR-TLVs defined in Section 4. For instance, the same
   time.

   The setupPriority Label Request
      Message may include the ER-TLV.

      - An LSR implicitly infers ordered control from the existence of a CRLSP should not be higher (numerically less)
   than its holdingPriority since it might bump an LSP and
      one or more CR-TLVs in the Label Request Message. This means that
      the LSR can still be bumped by
   next "equivalent" request.

   Bumping by default only happens as a last resort when there are no
   routes available configured for independent control for LSPs
      established as a given path.

   During the instantiation result of dynamic routing. However, when a path that must bump other paths, lower
   holding priority paths are bumped before higher priority paths. The
   decision as to which Label
      Request Message includes one or more of the available paths are bumped at each
   intermediate node by CR-TLVs, then ordered
      control is used to setup the new path CRLSP. Note that this is arbitrary.

4.2 ER-Hop TLV

   The contents also true
      for the loosely routed parts of a constraint-based route TLV CRLSP.

      - New status codes are a series defined to handle error notification for
      failure of variable
   length ER-Hop TLVs. Each ER-Hop TLV has established paths specified in the form:

         0                   1
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------//--------------+
        |L|    Type     |  Length       |       Contents         |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------//--------------+

L CR-TLV.

CR-LDP Specification             - 9 7 -                  Exp. Apr August 1999

   The L bit is an attribute

   Examples of the ER-Hop.  The L bit is set if the
   ER-Hop represents a loose hop CRLSP establishment are given in Appendix A to illustrate
   how the explicit route.  If the bit is mechanisms described in this draft work.

3.1 Required Messages and TLVs

   Any Messages, TLVs, and procedures not set, the ER-Hop represents a strict hop defined explicitly in this
   document are defined in the explicit route.

Type

   A seven-bit field indicating [LDP] Specification. The state
   transitions which relate to CR-LDP messages can be found in [LDP-
   STATE].

   The following subsections are meant as a cross reference to the type of contents [LDP]
   document and indication of the ER-Hop.
   Currently additional functionality beyond what's
   defined values are:

             Value                   Type
             -----                   ------------------------
             0                       Reserved
             1                       IPv4 prefix
             2                       IPv6 prefix
             32                      Autonomous system number

Length in [LDP] where necessary.

3.2 Label Request Message

   The Length field contains Label Request Message is as defined in 3.5.8 of [LDP] with the total length
   following modifications (required only if any of the ER-Hop CR-TLVs is
   included in bytes. It
   includes the L bit, Type and Length fields. The length must always be Label Request Message):

      - Only a multiple of 4, and at least 4.

Contents

   A variable length field containing single FEC-TLV may be included in the node or abstract node that Label Request
      Message. The CR-LSP FEC TLV should be used.

      - The Return Message ID TLV is MANDATORY.

      - The Optional Parameters TLV includes the consecutive nodes that make up definition of any of
      the explicit routed LSP.

4.3 Applicability

   The CR-TLV Constraint-based TLVs specified in this version of Section 4.

      - The Procedures to handle the specification is intended for
   unicast only. CRLSPs for multicast Label Request Message are FFS.

4.4 Semantics of augmented
      by the CR-TLV

   Like any other LSP an CRLSP is a path through a 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 procedures for processing 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 CR-TLVs as defined in order to better support
   the traffic sent over the LSP.
      Section 4.

      The reason encoding 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.

   A CRLSP is represented in a CR-LDP 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 as follows:

CR-LDP Specification             - 10 8 -                  Exp. Apr August 1999

   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

       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|   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

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

      - Only a constraint-based route TLV.  Each ER-Hop single Label-TLV may identify
   a group of nodes be included in the constraint-based route. 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 constraint-based
   route Mapping message is then transmitted by a path including all of the identified groups of nodes.

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

4.5 Strict and Loose ER-Hops following conditions:

      1. The L bit in the ER-Hop is a one-bit attribute.  If the L bit is set,
   then the value of the attribute LSR is "loose."  Otherwise, the value egress end of the attribute is "strict."  For brevity, we say that if the value of
   the ER-Hop attribute is loose then it is a "loose ER-Hop."
   Otherwise, it's a "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 CRLSP and strict nodes are always interpreted relative
   to their prior abstract nodes. an upstream mapping
      has been requested.

      2. The path between LSR received a strict node and its prior node MUST include only
   network nodes mapping from the strict node and its prior abstract node.

   The path between a loose node and its prior node MAY include other
   network nodes downstream next hop LSR for
      an CRLSP for which are not part of the strict node or its prior
   abstract node.

4.6 Loops

   While the constraint-based route TLV an upstream request is of finite length, still pending.

      The encoding for the
   existence of loose nodes implies that it CR-LDP Label Mapping Message is possible to construct
   forwarding loops during transients in the underlying routing
   protocol.  This may be detected by the originator of the constraint-
   based route through the use a path vector object as defined in [LDP].

4.7 ER-Hop semantics

4.7.1. ER-Hop 1:  The IPv4 prefix

   The contents of an IPv4 prefix ER-Hop are a 4 byte IPv4 address, 1 follows:

CR-LDP Specification             - 11 9 -                  Exp. Apr August 1999

   byte of prefix length, and 1 byte of padding.  The abstract node
   represented by this ER-Hop is the set of nodes which have an IP
   address which lies within this prefix.  Note that a prefix length of
   32 indicates a single IPv4 node.

   The length of the IPv4 prefix ER-Hop is 8 bytes.  The contents of the
   1 byte of padding must be zero on transmission and must not be
   checked on receipt.

      0

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |L|    Type
      |U|   Label Mapping (0x0400)   |      Message Length            | IPv4 Address (4 bytes)        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      IPv4 Address (Continued)                     Message ID                                |   Prefix      |0 0 0 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

   IPv4 Address 0x01

Length

   A one byte field indicating the total length of the TLV in bytes. It
   includes the L-bit, the Type, Length, the IP Address, and the Prefix
   fields. The length is always 8 bytes.

IP Address

   A four byte field indicating the IP Address.

Prefix Length

   1-32

Padding

   Zero on transmission.  Ignored on receipt.

4.7.2. ER-Hop 2:  The IPv6 address

CR-LDP Specification             - 12 -                    Exp. Apr 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |L|    Type
      |     Length    |   IPV6 address (16 bytes)                     FEC TLV                                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | IPV6 address (continued)                     Label TLV                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | IPV6 address (continued)              Label Request Message ID TLV  (mandatory)        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | IPV6 address (continued)                     LSPID TLV            (CR-LDP, mandatory)  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | IPV6 address (continued)                     Traffic  TLV         (CR-LDP, optional)   |   Prefix      |0 0 0 0 0 0 0 0|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

   0x02  IPv6 address

Length

3.4 Notification Message

   The Length contains the total length Notification Message is as defined in Section 3.5.1 of [LDP] and
   the ER-Hop Status TLV in bytes,
   including the Type and Length fields.  The Length encoding is always 20.

IPv6 address

   A 128-bit unicast host address.

Prefix Length

   1-128

Padding

   Zero on transmission.  Ignored on receipt.

4.7.3. ER-Hop 32:  The autonomous system number

   The contents as defined in Section 3.4.7 of [LDP].

   Establishment of an autonomous system (AS) number ER-Hop are Explicitly Routed LSP may fail for a 2 byte
   autonomous system number.  The abstract node represented variety of
   reasons.  All such failures are considered advisory conditions and
   they are signaled by this ER-
   Hop is the set 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 nodes belonging a CRLSP and
   the processing of the CR-TLV.

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

3.5 Release and Withdraw Messages

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

4. Protocol Specification

   The length Label Request Messages defined in [LDP] optionally carries one or
   more of the AS number ER-Hop 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 4 bytes. 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.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |L|    Type
     |U|F|         ER-TLV  (0x0800)  |      Length                   | Autonomous System number
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          ER-Hop TLV 1                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

CR-LDP Specification             - 13 -                    Exp. Apr 1999

   AS Number 0x20

Length

   A one byte field indicating the total length of the
     |                          ER-Hop TLV in bytes. It
   includes the L-bit, the Type, and Length, and the AS number fields.
   The length is always 4 bytes.

AS number 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 field indicating carrying the AS number.

4.8. Processing value of the Constraint-Based ER-TLV type which
      is 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

4.8.1. Selection (ER-Hop TLV)

   The contents of the next hop

   A Label Request message containing an ER-TLV are a constraint-based route series of variable length ER-Hop
   TLVs. Each ER-Hop TLV must
   determine has the next hop for this path.  Selection 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|          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 this next hop may
   involve a selection from a set contents of possible alternatives.
      the ER-Hop. Currently defined values are:

             Value                   Type
             -----                   ------------------------
             0x801                   IPv4 prefix
             0x802                   IPv6 prefix
             0x803                   Autonomous system number
             0x804                   LSPID

   Length
      Specifies the length of the value field in bytes.

   L bit
      The
   mechanism for making a selection from this set is implementation
   dependent and L bit is outside an attribute of the scope of this specification.
   Selection of particular paths ER-Hop. The L bit is also outside of set if the scope of this
   specification, but it is assumed that each node will make a best
   effort attempt to determine
      ER-Hop represents a loop-free path.  Note that such best
   efforts may be overridden by local policy.

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

      1) The node receiving the Label Request message must first
      evaluate in the first ER-Hop. explicit route. If the L bit is
      not set in set, the first ER-Hop and if the node is not part of the abstract node described
      by the first ER-Hop, it has received represents a strict hop in the message explicit route.

      The L bit in error, and
      should return the ER-Hop is a "Bad initial ER-Hop" error. one-bit attribute.  If the L bit is set
      and
      set, then the local node is not part value of the abstract node described by attribute is "loose."  Otherwise, the first ER-Hop,
      value of the node selects a next hop that attribute is along the
      path to "strict."  For brevity, we say that if
      the abstract node described by value of the first ER-Hop. If there ER-Hop attribute is no first ER-Hop, the message loose then it is also in error and the system
      should return a "Bad Constraint-Based Routing TLV" error.

      2) If there is no second ER-Hop, this indicates the end of the
      constraint-based route. The constraint-based route TLV should be
      removed from "loose
      ER-Hop."  Otherwise, it's a "strict ER-Hop."  Further, we say that
      the Label Request message.  This abstract node may or may not
      be the end of the LSP.  Processing continues with section 4.8.2,
      where a new constraint-based route TLV may be added to the Label
      Request message.

      3) If the node strict or loose ER-Hop is also a part of the 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 described by
      the second ER-Hop, then the and its prior node deletes MUST include
      only network nodes from the first ER-Hop strict node and
      continues processing with step 2, above.  Note that this makes the
      second ER-Hop into the first ER-Hop its prior abstract
      node.

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

CR-LDP Specification             - 14 12 -                 Exp. Apr August 1999

      4) The node determines if it is topologically adjacent to the
      abstract node described by the second ER-Hop.  If so,

   Contents
      A variable length field containing the node
      selects a particular next hop which is a member of the or abstract
      node.  The node then deletes that
      is the first ER-Hop and continues
      processing with section 4.8.2.

      5) Next, consecutive nodes that make up the node selects a next hop within explicit routed LSP.

4.3  Traffic Parameters TLV

   The following sections describe the abstract node CRLSP Traffic Parameters.  The
   required characteristics of a CRLSP are expressed by the first ER-Hop that Traffic
   Parameter values.

   A Traffic Parameters TLV, is along the path used to signal the abstract node of
      the second ER-Hop.  If no such path exists then there Traffic Parameter
   values. The Traffic Parameters are two
      cases:

      5a) If defined in the second ER-Hop is subsequent
   sections.

   The Traffic Parameters TLV contains a strict ER-Hop, then there is an
      error and the node should return Flags field, a "Bad strict node" error.

      5b) Otherwise, if the second ER-Hop is Frequency, a loose ER-Hop, then
   Weight, and the
      node selects any next hop that five Traffic Parameters PDR, PBS, CDR, CBS, EBS.  The
   Traffic Parameters TLV is along shown below:

      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| 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 path to value of the next
      abstract node.  If no path exists, then there ER-TLV type which
      is an error, and the
      node should return a "Bad loose node" error.

      6) Finally, the node replaces the first ER-Hop with any ER-Hop
      that denotes an abstract node containing 0x810.

   Length
      Specifies the next hop.  This is
      necessary so that when length of the constraint-based route value field in bytes.

   Flags
      The Flags field is received by 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 next hop, it will be accepted.

      7) Progress PDR.
                          F2 - Corresponds to the Label Request Message PBS.
                          F3 - Corresponds to the next hop.

4.8.2. Adding ER-Hops CDR.
                          F4 - Corresponds to the constraint-based route TLV

   After selecting a next hop, CBS.
                          F5 - Corresponds to the node may alter EBS.
                          F6 - Corresponds to the constraint-based
   route in the following ways.

   If, as part of executing the algorithm in section 4.8.1, the
   constraint-based route TLV Weight.

         Each flag Fi is removed, the node may add a new
   constraint-based route TLV.

   Otherwise, if the node is Negotiable Flag corresponding to a member of 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 abstract node for following code points defined:

                               0      - Unspecified
                               1      - Frequent
                               2      - VeryFrequest
                               3-255  - Reserved

   Reserved
      Zero on transmission.  Ignored on receipt.

   Weight
      An 8 bit unsigned integer indicating the first
   ER-Hop, then a series weight of ER-Hops may be inserted before the first
   ER-Hop or may replace CRLSP.
      Valid weight values are from 1 to 255.  The value 0 means
      that weight is not applicable for the first ER-Hop. CRLSP.

   Traffic Parameters
      Each ER-Hop in this series
   must denote an abstract node that Traffic Parameter is encoded as a subset 32 bit IEEE single-
      precision floating point number.  A value of the current abstract
   node.

   Alternately, if the first ER-Hop positive infinity is a loose ER-Hop,
      represented as an arbitrary
   series IEEE single-precision floating-point number with
      an exponent of ER-Hops may 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 inserted prior greater than or equal to the first ER-Hop.

4.8.3. Error subcodes

   In the processing described above, certain errors need to be reported
   as part value of the Notification message.  This section defines the status
   codes for the errors described above. CDR
      in a correctly encoded Traffic Parameters TLV.

4.3.1 Semantics

4.3.1.1 Frequency

CR-LDP Specification             - 15 14 -                 Exp. Apr August 1999

      Status Code                                    Type
      --------------------------------------         ----------
      Bad Constraint-Based Routing TLV Error         0x04000001
      Bad Strict Node Error                          0x04000002
      Bad Loose  Node Error                          0x04000003
      Bad Initial ER-Hop Error                       0x04000004
      Resource Unavailable                           0x04000005
      Service Class Unavailable                      0x04000006
      Traffic Parameters Unavailable                 0x04000007

5.0 CRLSP Service Classes and Traffic Parameters

   The following sections describe Frequency specifies at what granularity the CDR allocated to the
   CRLSP Service Classes (SCs), and
   their associated traffic parameters.

   The CRLSP Service Class is signaled in made available.  The value VeryFrequently means that the SC Field of
   available rate should average at least the CR-TLV
   defined in Section 4.1.

   Three Service Classes are currently supported by CR-LDP:

            Service Class                                  Value
            --------------------------                     -----
            Best Effort           (BE)                     0x0
            Throughput Sensitive  (TS)                     0x1
            Delay Sensitive       (DS)                     0x2

   These service classes are specified in CDR when measured over any
   time interval equal to or longer than the following sections.

5.1 Best Effort (BE) shortest packet time at the
   CDR.  The request 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 BE SC implies CDR.
   The value Unspecified means that there are no expected service
   guarantees from the network. The service CDR MAY be provided by at any
   granularity.

4.3.1.2  Peak Rate

   The Peak Rate defines the network is maximum rate at which traffic SHOULD be
   sent to the familiar best effort service. CRLSP. The Peak Date Rate (PDR) is useful for the only traffic parameter that may purpose of
   resource allocation. If resource allocation within the MPLS domain
   depends on the Peak Rate value then it should be
   specified with enforced at the BE SC.
   ingress to the MPLS domain.

   The specification Peak Rate is defined in terms of the two Traffic Parameters PDR allows the
   network to perform traffic shaping
   and policing functions.

5.2 Throughput Sensitive (TS)

   In the service model for PBS, see section 4.3.1.5 below.

4.3.1.3 Committed Rate

   The Committed Rate defines the Throughput Sensitive SC, rate that the network MPLS domain commits to deliver with high probability user datagrams at a rate
   be available to the CRLSP.

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

4.3.1.4 Excess Burst Size

   The user Excess Burst Size may transmit be used at a rate
   higher than CDR but datagrams 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 CDR would have 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 lower
   probability positive infinite
   value of being delivered. either PDR or PBS implies that arriving packets are never 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 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
          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" 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).

   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 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].

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 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F| 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].

   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.

   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 higher the holding priority, the less likely it is for 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.

      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|      LSPID-TLV  (0x0821)  |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       Reserved                |      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].

   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.

   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 LSR ID.

4.6 Resource Class (Color) TLV

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

CR-LDP Specification             - 19 -                 Exp. August 1999

   networks 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|      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" or "colors" of links
      the CRLSP can traverse.

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
   which have an IP 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|         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 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|          0x802            |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |L|             Reserved                        |    PreLen     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  IPV6 address                                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  IPV6 address (continued)                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  IPV6 address (continued)                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  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:  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|          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 user sends at a rate length of CDR or
   lower the network commits value field in bytes.

   L Bit
      Set to deliver with high probability all the
   user datagrams. 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

   The TS SC has an associated tolerance LSPID is used to identify the burstiness of arriving 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             - 16 22 -                 Exp. Apr August 1999

   user datagrams. This tolerance is

   being established with an existing 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|          0x804            |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |L|          Reserved           |               Local LSPID     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Ingress LSR Router ID                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

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

   Type
      LSPID 0x804

   Length
      Specifies the traffic parameter
   Committed Burst Tolerance (CBT).

   Ideally, a TS CRLSP request carries with it a rich set length of three
   traffic parameters (PDR, CDR, and CBT) that accurately describe its
   traffic characteristics. This allows the network value field in bytes.

   L Bit
      Set to perform resource
   reservation, traffic shaping, and traffic policing.

   However, for the sake of simplicity of the service definition, the
   CDR is the only parameter that MUST always be specified for indicate Loose hop.
      Cleared to indicate a TS
   CRLSP. strict hop.

   Reserved
      Zero on transmission.  Ignored on receipt.

   Local LSPID
      A peak data rate parameter (PDR) and a CBT are optional
   traffic parameters for 2 byte field indicating the TS SC.

   The network should make every effort LSPID which is unique
      with reference to preserve ordering the its Ingress LSR.

   Ingress LSR Router ID
      A 4 byte field indicating the Ingress LSR ID.

4.8. Processing of the
   delivered datagrams Explicit Route TLV

4.8.1. Selection of the next hop

   A Label Request Message containing a TS CRLSP.

   Network traffic that requires explicit route TLV must
   determine the next hop for this path.  Selection of this next hop may
   involve a low packet loss ratio at selection from a given CDR
   but set of possible alternatives.  The
   mechanism for making a selection from this set is not particularly sensitive to delay implementation
   dependent and jitter (e.g., network
   control traffic) is suited to the TS SC. The selection outside of the TS SC scope of this specification.
   Selection of particular paths is used to signal to the various nodes along also outside of the path scope of this
   specification, but it is assumed that the
   queuing and scheduling mechanisms used to handle the CRLSP should
   provide each node will make a low packet loss ratio.

5.3 Delay Sensitive (DS)

   In the service model for the Delay Sensitive SC, the network commits best
   effort attempt to deliver with high probability user datagrams at a rate of CDR
   (Committed Data Rate) with minimum delay and delay variation. The
   user MUST transmit data at determine a rate of CDR or lower in order to be
   eligible for DS service. Datagrams in excess of CDR loop-free path.  Note that such best

CR-LDP Specification             - 23 -                 Exp. August 1999

   efforts may be discarded overridden by local policy.

   To determine the network. If next hop for the user sends at path, a rate of CDR or lower node performs the
   network commits to deliver with high probability all user datagrams
   with low delay and delay variation. If following
   steps:

      1) The node receiving the user sends at a rate
   higher than CDR Label Request Message must first
      evaluate the network does first ER-Hop. If the L bit is not provide any guarantees on set in the
   excess traffic.

   The Delay Sensitive SC has an associated tolerance to first
      ER-Hop and if the burstiness
   of arriving user datagrams. This tolerance node is defined not part of the abstract node described
      by the traffic
   parameter Committed Burst Tolerance (CBT).

   Ideally, a DS CRLSP request carries with first ER-Hop, it has received the message in error, and
      should return a rich "Bad initial ER-Hop" error. If the L bit is set of three
   traffic parameters (PDR, CDR,
      and CBT) the local node is not part of the abstract node described by
      the first ER-Hop, the node selects a next hop that accurately describe its
   traffic characteristics. This allows is along the network
      path to perform resource
   reservation, traffic shaping and policing.

   However, for the sake of simplicity of the service definition, abstract node described by the
   CDR first ER-Hop. If there
      is no first ER-Hop, the only parameter that MUST always be specified for a DS
   CRLSP.  A peak data rate parameter (PDR) message is also in error and the system
      should return a CBT are optional
   traffic parameters for "Bad Explicit Routing TLV" error.

      2) If there is no second ER-Hop, this indicates the DS SC. end of the
      explicit route. The network explicit route TLV should make every effort to preserve ordering of be removed from the

CR-LDP Specification             - 17 -                    Exp. Apr 1999

   delivered datagrams
      Label Request Message.  This node may or may not be the end of the
      LSP.  Processing continues with section 4.8.2, where a DS CRLSP.

   Network traffic that requires new
      explicit route TLV may be added to the Label Request Message.

      3) If the node is also a low delay part of the abstract node described by
      the second ER-Hop, then the node deletes the first ER-Hop and delay variation at a
   given CDR (e.g., voice traffic) is suited to
      continues processing with step 2, above.  Note that this makes the DS SC. The selection
      second ER-Hop into the first ER-Hop of the DS SC next iteration.

      4) The node determines if it is used to signal topologically adjacent to the various nodes along
      abstract node described by the path
   that second ER-Hop.  If so, the queuing and scheduling mechanisms used to handle node
      selects a particular next hop which is a member of the CRLSP
   should provide low delay and delay variation.

5.4  Traffic Parameters

   The CRLSP traffic parameters are defined in this section. abstract
      node.  The traffic parameters CDR, CBT node then deletes the first ER-Hop and PDR are defined in terms of continues
      processing with section 4.8.2.

      5) Next, the node selects a
   TOKEN_BUCKET_TSPEC as specified in [RFC2215]. The following mapping next hop within the abstract node of parameters in
      the TOKEN_BUCKET_TSPEC is used:

                  Token rate,                    r = CDR
                  Bucket depth,                  b = CBT
                  Peak traffic rate,             p = PDR
                  Minimum policed unit,          m = 1
                  Maximum packet size,           M = MTU

   The Traffic Parameters TLV first ER-Hop that is used to signal the traffic
   characteristics of along the CRLSP. These traffic parameters are used path to
   perform functions such as resource reservation, Shaping, and
   Policing. See [SIN] for more details. The encoding for the Traffic
   Parameters TLV is:

      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|  Traffic   TLV  (0x0810)  |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            PDR TLV                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            CDR TLV                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            CBT TLV                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.4.1  Peak data rate (PDR) TLV

   The value of traffic parameter PDR abstract node of
      the second ER-Hop.  If no such path exists then there are two
      cases:

      5a) If the second ER-Hop is given as a positive integer in
   bytes per second. Zero strict ER-Hop, then there is not an
      error and the node should return a valid value of PDR.

   The user may specify "Bad strict node" error.

      5b) Otherwise, if the value of PDR depending second ER-Hop is a loose ER-Hop, then the SC of
      node selects any next hop that is along the CRLSP.
   Specifying path to the PDR allows next
      abstract node.  If no path exists within the network to use traffic management
   functions such as shaping. MPLS domain, then
      there is an error, and the node should return a "Bad loose node"
      error.

      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             - 18 24 -                 Exp. Apr 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|  PDR

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

4.8.2. Adding ER-Hops to the explicit route TLV  (0x0811)        |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       PDR

   After selecting a next hop, the node may alter the explicit route in Bytes/sec                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.4.2. Committed Data Rate (CDR)

   The value
   the following ways.

   If, as part of traffic parameter CDR executing the algorithm in section 4.8.1, the explicit
   route TLV is given as removed, the node may add a positive integer in
   bytes per second. Zero new explicit route TLV.

   Otherwise, if the node is not a valid  value member of CDR.

   The user may provide the abstract node for the first
   ER-Hop, then a requested value series of CDR 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 CRLSP request
   depending on current abstract
   node.

   Alternately, if the SC first ER-Hop is a loose ER-Hop, an arbitrary
   series of ER-Hops may be inserted prior to the CRLSP. 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|  CDR TLV  (0x0812)          0x823            |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       CDR in Bytes/sec
     |P|                        Reserved                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.4.3. Committed Burst Tolerance (CBT)

   The value of traffic parameter CBT is given

   U bit
      Unknown TLV bit. As defined in bytes.  Zero is not a
   valid  value of CBT.

   The requested value of CBT MUST be no smaller than [LDP].

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

   Type
      Pinning-TLV type 0x823

   Length
      Specifies the MTU length of the
   originating interface.

   The user may provide a requested value of CBT field in the CRLSP request.
   If the user chooses not bytes.

   P Bit
      The P bit is set to specify a 1 to indicate that route pinning is requested.
      The P bit is set to 0 to indicate that route pinning is not
      requested value of CBT and the
   network

   Reserved
      Zero on transmission.  Ignored on receipt.

4.10 CRLSP FEC Element

CR-LDP Specification             - 25 -                 Exp. August 1999

   A new FEC element is policing the traffic, then any excess traffic will introduced in this specification to support CR-
   LSPs. The CRLDP FEC Element is an opaque FEC.

      FEC Element     Type      Value
      type name

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

      CRLSP FEC Element
          To be
   dropped by the network. 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|  CBT TLV  (0x0813)          FEC(0x0100)      |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           CBT in Bytes CR-LSP (4)    |          Reserved                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6. Open Issues

   This section captures the issues that need further study.

CR-LDP Specification             - 19 -                    Exp. Apr 1999

   1) Review the FSM described in Appendix B and extend it by the CR-TLV
   processing

   U bit
      Unknown TLV bit. As defined in Sections 4.8.1 and 4.8.2.

   2) Consider if all three traffic parameters have to be signaled at
   all times and if the network should supply default values for the
   missing parameters.

   3) Consider the following extensions to the CR-TLV:

      3.1) Changing the 'P' [LDP].

   F bit to "next hop flag" and making it a 2-bit
      wide field with the following values:

         - 00 "local repair", which means if it belongs to a loosely
         routed segment, and the LSR detects a next hop change, the LSR
         will try to establish a new LSP from this point on and switch
         it over to the new LSP when it is setup.

         - 01 "global repair", which means when the LSR detects a next
         hop change, the LSR will tear down the LSP, the ingress LSR
         will try to reestablish another LSP through the new path.

         - 10 "pinned", which means that the loosely routed segments
         must remain pinned down.

         - 11 Reserved.

      3.2) Adding one more field "LSPID" before ER-Hop TLV.  LSPID can
      be used to identify a network wide unique CRLSP.

         - The first 4 bytes carrying
      Forward unknown TLV bit.  As defined in [LDP].

   Type
      FEC TLV type 0x0100

   Length
      Specifies the ingress LSR IP address

         - The second 4 bytes carrying length of the unique ID value assigned by
         the ingress LSR.

   4) Consider the following extension to the ER-Hop TLV:

      For Type field, add one more type, LSPID, which means the current
      CRLSP will go through another CRLSP which is identified with this
      LSPID value:

       Value field in bytes.

   CR-LSP FEC Element Type
       -----   -----
       4       LSPID

      Extend processing
      0x04

   Reserved
      Zero on transmission.  Ignored on receipt.

4.11 Error subcodes

   In the LSPID ER-Hop processing described above, certain errors need to be reported
   as follows: If the type of ER-
      Hop is LSPID, and the other end of this CRLSP is not part of the
      constraint-based route TLV, add it to the constraint-based TLV
      with L bit turned off.

   5) Consider traffic parameter negotiation and Notification Message.  This section defines the ability to change status
   codes for the traffic parameters associated with an already established path errors described in this specification.

CR-LDP Specification             - 20 26 -                 Exp. Apr August 1999

   without tearing the old path down.

7.

      Status Code                                       Type
      --------------------------------------         ----------
      Bad Explicit Routing TLV Error                 0x04000001
      Bad Strict Node Error                          0x04000002
      Bad Loose  Node Error                          0x04000003
      Bad Initial ER-Hop Error                       0x04000004
      Resource Unavailable                           0x04000005
      Traffic Parameters Unavailable                 0x04000006
      Setup abort                                    0x04000007

5. Security

   No security issues are discussed in this version of

   Pre-emption has to be controlled by the draft.

8. MPLS domain.

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

   Normal routing can be bypassed by Traffic Engineered LSPs.

6. Acknowledgments

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

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

9.

7. References

   [FRAME] Callon

   [LDP]   Andersson et al, "Framework for Multiprotocol Label Switching", "Label Distribution Protocol Specification"
           work in progress (draft-ietf-mpls-framework-02), November 1997. (draft-ietf-mpls-ldp-03), Feb. 1999.

   [ARCH]  Rosen et al, "Multiprotocol Label Switching Architecture",
           work in progress (draft-ietf-mpls-arch-02), July 1998.

   [LDP] Andersson (draft-ietf-mpls-arch-04), Feb. 1999.

   [FRAME] Callon et al, "Label Distribution Protocol Specification" "Framework for Multiprotocol Label Switching",
           work in progress (draft-ietf-mpls-ldp-02.txt), (draft-ietf-mpls-framework-02), November
           1997.

   [TER]   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.txt, (draft-guerin-expl-path-rsvp-
   01)
           November 1997.

   [TER] Awduche et al, "Requirements for Traffic Engineering Over
   MPLS", work in progress (draft-awduche-mpls-traffic-eng-00), April
   1998.

CR-LDP Specification             - 27 -                 Exp. August 1999

   [VPN1]  Heinanen et al, "MPLS Mappings of Generic VPN Mechanisms",
           work in progress (draft-heinanen-generic-vpn-mpls-00),
           August 1998.

   [VPN2]  Jamieson et al, "MPLS VPN Architecture" work in progress
           (draft-jamieson-mpls-vpn-00), August 1998.

   [RFC2215] S. Shenker and J. Wroclawski, General Characterization
   Parameters for Integrated Service Network Elements, RFC 2215, Sep
   1997.

   [SIN] B. Jamoussi, N. Feldman, and L. Andersson, "MPLS Ships

   [VPN3]  T. Li, "CPE based VPNs using MPLS", work in the
   Night with ATM", (draft-jamoussi-mpls-sin-00.txt), August progress (draft-
           li-mpls-vpn-00.txt), October 1998.

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

CR-LDP Specification             - 21 28 -                 Exp. Apr August 1999

10.

8. Author Information

Osama S. Aboul-Magd                       Loa Andersson
Nortel Networks                           Director Bay Architecture Lab, EMEA Lab,EMEA
P O Box 3511 Station C                    Kungsgatan 34, PO Box 1788
Ottawa, ON K1Y 4H7                        111 97 Stockholm, Sweden
Canada                                    phone: +46 8 441 78 34
phone: +1 613 763-5827                    mobile +46 70 522 78 34
   e-mail:
osama@NortelNetworks.com                  loa_andersson@baynetworks.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
   Email:
phone: +1 613 763-4534                    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
Fax:   972 996 5902
   Email:
ram.dantu@aud.alcatel.com

   Paul Doolan
   Ennovate Networks
   330 Codman Hill Rd
   Marlborough MA 01719
   Phone: 978-263-2002
   email: pdoolan@ennovatenetworks.com

Nancy Feldman                             Andre Fredette
IBM Corp.                                 Nortel Networks
17 Skyline Drive
   Hawthorne NY 10532
   Phone:  914-784-3254
   email: nkf@us.ibm.com

   Andre Fredette
   Nortel Networks                          3 Federal Street
Hawthorne NY 10532                        Billerica, MA 01821
   email:
Phone:  914-784-3254                      fredette@baynetworks.com
nkf@us.ibm.com

Eric Gray                                 Joel M. Halpern
Lucent Technologies, Inc                  Newbridge Networks Inc.
1600 Osgood St.                           593 Herndon Parkway
North Andover, MA  01847
   email: ewgray@lucent.com

CR-LDP Specification             - 22 -                    Exp. Apr 1999

   Joel M. Halpern
   Newbridge Networks Inc.
   593 Herndon Parkway                  Herndon, VA 20170
   email: jhalpern@newbridge.com
Phone: 603-659-3386                       phone: 1-703-736-5954
   fax:   1-703-736-5959
ewgray@lucent.com                         jhalpern@newbridge.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: +358 303 944 808
   Email: 41 500 4808                     etxfiff@etxb.ericsson.se
jh@telia.fi

CR-LDP Specification             - 29 -                 Exp. August 1999

Bilel Jamoussi                            Timothy E. Kilty
Nortel Networks                           Northchurch Communications
P O Box 3511 Station C                    5 Corporate Drive,
Ottawa, ON K1Y 4H7
   Canada
   phone: +1 613 765-4814
   email: jamoussi@NortelNetworks.com

   Timothy E. Kilty
   Northchurch Communications
   5 Corporate Drive,                        Andover, MA 018110
Canada                                    phone: 978 691-4656
   Email:
phone: +1 613 765-4814                    tkilty@northc.com
jamoussi@NortelNetworks.com

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

Kenneth Sundell
   Ericsson
   SE-126 25 Stockholm
   Sweden

CR-LDP Specification             - 23 -                    Exp. Apr 1999

   email: kenneth.sundell@etx.ericsson.se                           Pasi Vaananen
Ericsson                                  Nokia Telecommunications
SE-126 25 Stockholm                       3 Burlington Woods Drive, Suite 250
Sweden                                    Burlington, MA 01803
kenneth.sundell@etx.ericsson.se           Phone: +1-781-238-4981
   Email:
                                          pasi.vaananen@ntc.nokia.com

Tom Worster                               Liwen Wu
General DataComm, Inc.                    Alcatel U.S.A
5 Mount Royal Ave.
   Marlboro MA 01752
   Email: tom.worster@gdc.com

   Liwen Wu
   Alcatel U.S.A                        44983 Knoll Square
Marlboro MA 01752                         Ashburn, Va. 20147
tom.worster@gdc.com                       USA
                                          Phone: (703) 724-2619
                                          FAX:   (703) 724-2005
   Inet:
                                          liwen.wu@adn.alcatel.com

CR-LDP Specification             - 30 -                 Exp. August 1999

Appendix A: CRLSP Establishment Examples

A.1 Strict Constraint-Based 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.

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

                             a         b         c
                    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 CR-TLV ER-TLV is composed by a vector of three ER-Hop TLVs <a, b, c>.
   The ER-Hop TLVs used in this example are of type 0x01 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 CR-TLV 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.

CR-LDP Specification             - 24 -                    Exp. Apr 1999

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

   At LSR3, a similar processing to the CR-TLV ER-TLV takes place except that
   the incoming CR-TLV ER-TLV = <b, c> and the outgoing CR-TLV 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 CR-TLV 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 CR-TLV. ER-TLV.
      LSR4 does not add a new CR-TLV. 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 CR-TLV 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

CR-LDP Specification             - 25 -                    Exp. Apr 1999
   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 the constraint-based 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 CR-TLV ER-TLV defining the constraint-based explicitly routed path. In our
   example the list of hops in the ER-Hop TLV is supposed to contain an
   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 CR-TLV 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:

CR-LDP Specification             - 26 -                    Exp. Apr 1999

      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 1999

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

      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             - 27 -                    Exp. Apr 1999

Appendix B. CR-LDP Finite State Machine

      In this description of the CR-LDP FSM, behavior  relating  to  the
      state  of  LDP  messages  is  assumed to be defined (implicitly or
      explicitly) in [LDP].  In particular, LDP  is  assumed  to  retain
      state  information  relating  a Label Request made of a downstream
      neighbor to the Label Request  message(s)  of  upstream  neighbors
      (downstream-on-demand  mode)  which the (downstream) Label Request
      is meant  to  satisfy.   This  will  be  true  of  many  potential
      applications  of  LDP,  of which CR-LDP is an example.  Minimally,
      this state should include message IDs of Label Requests (both sent
      and  received)  and the LSR(s) from which pending Label Request(s)
      were received.

      The FSM describes CR-LDP behavior in the following operations:

      - Start of CRLSP setup (in which a Label Request is sent);

      - Processing the CR-TLV portion of Label Requests;

      - Completion of CRLSP setup (via Label Mapping messages);

      - Notification of originator when:

         - a loop is detected in a loose constraint-based route segment,

         - an ER-Hop is not reachable from a previous ER-Hop,

         - a next ER-Hop is strict and not  directly  connected  to  the
         current LSR or

         - the current LSR is strict and is not (part  of  the  abstract
         node in) the first ER-Hop in the CR-TLV;

      - Withdrawing a CRLSP.

   For the description, the following pictorial representations  may  be
   used as an aid to understanding:

            LSR 1              LSR 2          ...          LSR n

           .-----.            .-----.                     .-----.
           | ER  |            | ER  |                     | ER  |
           `-----'            `-----'                     `-----'
               | CR-TLV  CR-TLV ^ | CR-TLV           CR-TLV ^
               |  Next          | |  Next                   |
               |  Hop           | |  Hop                    |
               V                | V                         |
           .-----. Label      .-----. the CRLSP, it returns a Label Mapping Message, that will
      traverse the same path as the Label   .-----.
           | LDP |----------->| LDP |-------> ... ------->| LDP |
           `-----' Request    `-----' Request     Request `-----' Message in the
      opposite direction.

CR-LDP Specification             - 28 34 -                 Exp. Apr August 1999

                          CRLSP Setup propagation

               LSR 1              LSR 2          ...          LSR n

              .-----.            .-----.                     .-----.
              | ER  |            | ER  |                     | ER  |
              `-----'            `-----'                     `-----'
                ^ Status                                 Status  |
                |                                       Previous |
                |                                         Hop    |
                |                                                V
              .-----. Label      .-----. Label       Label   .-----.
              | LDP |<-----------| LDP |<------- ... <-------| LDP |
              `-----' Mapping    `-----' Mapping     Mapping `-----'

                             CRLSP Status propagation

                        .---------------.
                        | ER            |       .---------------.
                        |     Link/Call |       | LDP           |
                        |     Admission |       |               |
                        |      Control  |       |      Label    |
                        `---------------'       |    Allocation |
                                                `---------------'

                                     Related Tasks

B.1. CR-LDP Primitives

      The following sections describe

Appendix B. QoS Service Examples

B.1 Service Examples

   Construction of an end-to-end service is  the logical interactions between
      Constrain-based Route and LDP state machines in terms  result  of
      primitives  the  rules
   enforced  at  the  edge and the treatment that describe packets receive at the minimal information exchange
      required.  These assume an asynchronous exchange model involving
      locally significant IDs
   network nodes. The rules define the traffic conditioning actions that is used
   are  implemented  at  the  edge  and they include policing with pass,
   mark, and drop capabilities.  The  edge  rules  are  expected  to tie status  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 treatment at a request network node is usually  referred  to  as  the initial setup and to allow LDP to relate incoming/outgoing
      Label Request messages.  A synchronous model - possibly based on
      multiple threads -
   local  behavior.  Local behavior could be specified in many ways. One
   example for local behavior specification  is also possible  the  service  frequency
   introduced   in   section   4.3.2.1.,   together  with  the  resource
   reservation rules implemented at the nodes.

   Edge rules and would eliminate local behaviors can be viewed  as  the need  main  building
   blocks  for IDs.

B.1.1. CR to LDP Primitives

      LDP_SEND_REQ( TLV_List, To_LSR, Identifier )

        TLV_List

          TLVs to be sent to a neighboring LSR; includes at least an  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             - 29 35 -                 Exp. Apr August 1999

          CR-TLV and may contain additional TLVs (i.e. QoS TLVs).

        To_LSR

          The neighbor LSR

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

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 which a Label Request is 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 sent.

        Identifier

          Locally significant unique identifier.  May be used discarded.

   The TS refers to
          associate a generic throughput sensitive service where the Label Request
   network commit to be sent either deliver with high probability user datagrams at a Label
          Request that was previously received (e.g. - LSR 2 above)
          or
   rate of at least CDR. The user may transmit at a subsequent CRLSP Status (e.g. - LSR 1 above).

      LDP_SEND_RSP( Status, Identifier )

        Status

          Status rate higher than CDR
   but datagrams in excess of CDR would have a specific CRLSP Setup Request.  A Status lower probability of zero
          indicates success; other Status values
   being delivered.

   The BE is the best effort service and it implies that there are given in Error
          Subcodes section.  This Status 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 carried requested in Label Mapping or
          Notification messages to this case.

   The first step is the originator specification of the CRLSP setup.

        Identifier

          Locally significant unique identifier used to associate traffic parameters in the
          Label Mapping to be sent with a Label Request received (e.g.
          LSR n above).

B.1.2. LDP to CR Primitives

      CR_RECEIVED_REQ( TLV_List, Identifier )

        TLV_List

          TLVs
   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. Since all the traffic parameters are
   included in the signaling  message, appropriate values must be processed by
   assigned to all of them. For DS service, the local constraint-based route
      function.

        Identifier

         Locally significant unique identifier used CDR and the CBS values
   are set equal to associate the
         received request either with a subsequent further request
         or a response.  For example, PDR and the identifier provided here
         would be used in a subsequent LDP_SEND_REQ or LDP_SEND_RSP.

      CR_LSP_STATUS( Status, Identifier )

        Status

          Status of a specific CRLSP Setup Request.  A Status PBS respectively. An indication of zero
          indicates success; other Status
   whether the parameter values are given in section
          Error Subcodes.  This Status originated at the remote LSR

CR-LDP Specification             - 30 -                    Exp. Apr 1999

          which either completed subject to negotiation is flagged.

   The transport characteristics of the CRLSP setup or determined DS service requires that
          CRLSP setup could not
   Frequent frequency to be done.

        Identifier

          Locally significant unique identifier used requested to associate reflect the
          received response with real-time delay
   requirements of the original request.  For example,
          this identifier would be service.

   In addition to the same as was used in transport characteristics, both the initial
          LDP_SEND_REQ.

B.2. CR-LDP States

      This document defines 3 states relative to any one specific CRLSP.
      They are:

         CR_Non_Existant - no state information exists relative network
   provider and the customer need to this
         CRLSP;

         CR_In_Progress - LDP_SEND_REQ has been called in result agree on the actions enforced at
   the edge. The specification of external input (e.g. - management);

         CR_Established - a successful status has been received from
         an earlier setup.

      These states are defined such that no additional state those actions is required expected to support CRLSPs using LDP at intermediate LSRs than is already
      required in LDP.

B.3. CR-LDP Events

      This document defines 4 events impacting any one specific CRLSP.
      They are:

         CR_Start - be a CRLSP is required based on an external stimulus
         (e.g. - management);

         CR_Req_Received - further CRLSP setup processing part
   of the service level agreement (SLA) negotiation and is required
         based on CR_RECEIVED_REQ (i.e. - from an upstream LSR's CRLSP
         Label Request);

         CR_Setup_Complete - CRLSP setup has been successfully completed
         based on CR_LSP_STATUS (with success status);

         CR_LSP_Failure - Either a CRLSP could 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 as
         requested, or a setup CRLSP has dropped; based on CR_LSP_STATUS
         (with error status).

B.4. CR-LDP Transitions

      State transitions are defined as follows: following the normal LDP procedures. Each

CR-LDP Specification             - 31 36 -                 Exp. Apr August 1999

      State                 Event              Action  New State
      ====================  =================  ======  ===============
      CR_Non_Existant       CR_Start            1      CR_In_Progress
      CR_Non_Existant       CR_Req_Rec          2      CR_Non_Existant
      CR_In_Progress        CR_Setup_Complete          CR_Established
      CR_In_Progress        CR_LSP_Failure      3      CR_Non_Existant
      CR_Established        CR_LSP_Failure      3      CR_Non_Existant

      Actions:

         1) Establish CRLSP state, create CR-TLV information,
      LDP_SEND_REQ.
         2) Process CR-TLV (as described in "Processing of
            the Constraint-Based Route TLV" section)

   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
            LDP_SEND_REQ the PDR, the PBS, or LDP_SEND_RSP.
         3) Remove state information relative both.
   The new parameters 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 CRLSP (may notify
            management, other external source initially requiring
      setup). example we assume that a throughput sensitive (TS) service is
   requested. For  resource allocation the purposes of this transition table, illegal transitions
      (not included 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 table) 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 PDR and 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 values are ignored. echoed back in the Label Mapping
   Message. LSRs might need to re-adjust their resources based on the
   new traffic parameter values.