VCID for LDP: VCID Notification over ATM link for LDP

Network Working Group                                          K. Nagami
Request for Comments: 3038                                    Y. Katsube
Category: Standards Track                                  Toshiba Corp.
                                                               N. Demizu
                                                        WaterSprings.ORG
                                                                H. Esaki
                                                          Univ. of Tokyo
                                                               P. Doolan
                                                       Ennovate Networks
                                                            January 2001

                VCID Notification over ATM link for LDP

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   The Asynchronous Transfer Mode Label Switching Router (ATM-LSR) is
   one of the major applications of label switching.  Because the ATM
   layer labels (VPI and VCI) associated with a VC rewritten with new
   value at every ATM switch nodes, it is not possible to use them to
   identify a VC in label mapping messages.  The concept of Virtual
   Connection Identifier (VCID) is introduced to solve this problem.
   VCID has the same value at both ends of a VC.  This document
   specifies the procedures for the communication of VCID values between
   neighboring ATM-LSRs that must occur in order to ensure this
   property.

1. Introduction

   Several label switching schemes have been proposed to integrate Layer
   2 and Layer 3.  The ATM Label Switching Router (ATM-LSR) is one of
   the major applications of label switching.

   In the case of ATM VCs, the VPI and VCI labels are, in the general
   case, rewritten with new values at every switch node through which
   the VC passes and cannot be used to provide end to end identification
   of a VC.

   In the context of MPLS 'stream', which are classes of packets that
   have some common characteristic that may be deduced by examination of
   the layer 3 header in the packets, are bound to layer 2 'labels'. We
   speak of stream being 'bound' to labels.  These bindings are conveyed
   between peer LSRs by means of a Label Distribution Protocol [LDP].

   In order to apply MPLS to ATM links, we need some way to identify ATM
   VCs in LDP mapping messages.  An identifier called a Virtual
   Connection ID (VCID) is introduced.  VCID has the same value at both
   ends of a VC.  This document specifies the procedures for the
   communication of VCID values between neighboring ATM-LSRs that must
   occur in order to ensure this property.

2. Overview of VCID Notification Procedures

2.1 VCID Notification procedures

   The ATM has several types of VCs (transparent point-to-point
   link/VP/PVC/SVC).  A transparent point-to-point link is defined as
   one that has the same VPI/VCI label at both ends of a VC.  For
   example, two nodes are directly connected (i.e., without intervening
   ATM switches) or are connected through a VP with the same VPI value
   at both ends of the VP.

   There are two broad categories of VCID notification procedures;
   inband and outband.  The categorization refers to the connection over
   which the messages of the VCID notification procedure are forwarded.
   In the case of the inband procedures, those messages are forwarded
   over the VC to which they refer.  In contrast the out of band
   procedures transmit the messages over some other connection (than the
   VC to which they refer).

   We list below the various types of link and briefly mention the VCID
   notification procedures employed and the rational for that choice.
   The procedures themselves are discussed in detail in later sections.

   Transparent point-to-point link : no VCID notification
       VCID notification procedure is not necessary because the label
       (i.e., VPI/VCI) is the same at each end of the VC.

   VP : inband notification or VPID notification or no notification
    - Inband notification
      VCID notification is needed because the VPI at each end of the VC
      may not be the same.  Inband VCID notification is used in this
      case.

    - VPID notification
      VCID notification is needed because the VPI at each end of the VC
      may not be the same.  VPID notification is used in this case.

    - No notification
      If a node has only one VP to a neighboring node, VCID notification
      procedure is not mandatory.  The VCI can be used as the VCID.
      This is because the VCI value is the same at each end of the VP.

   PVC : inband notification
      Inband VCID notification is used in this case because the labels
      at each end of the VC may not be the same.

   SVC : there are three possibilities
    - Outband notification
      If a signaling message has a field which is large enough to carry
      a VCID value (e.g., GIT [GIT]), then the VCID is carried directly
      in it.

    - Outband notification using a small-sized field
      If a signaling message has a field which is not large enough to
      carry a VCID value, this procedure is used.

    - Inband notification
      If a signaling message can not carry user information, this
      procedure is used.

      When an LSP is a point-to-multipoint VC and an ATM switch in an
      LSR is not capable of VC merge, it may cause problems in
      performance and quality of service.  When the LSR wants to add a
      new leaf to the LSP, it needs to split the active LSP temporarily
      to send an inband notification message.

2.2 VC direction

   A VC has a directionality.  The VCID procedure for a VC is always
   triggered from the upstream node of the VC, i.e., the upstream node
   notifies the downstream node of the VCID.

   If bidirectional use of a label switched VC is allowed, the label
   switched VC is said to be bidirectional.  In this case, two VCID
   procedures are taken, one for each direction.

   If bidirectional use of a label switched VC is not allowed, the label
   switched VC is said to be unidirectional.  In this case, only one
   VCID procedure is taken for the allowed direction.

   VC directionality is communicated through LDP.

3. VCID Notification Procedures

3.1 Inband Notification Procedures

3.1.1 Inband Notification for Point-to-point VC

   VCID notification is performed by transmitting a control message
   through the VC newly established (by signalling or management) for
   use as an label switched path (LSP).  The procedure for VCID
   notification between two nodes A and B is detailed below.

   0. The node A establishes a VC to the destination node B (by
      signalling or management).

   1. The node A selects a VCID value.

   2. The node A sends a VCID PROPOSE message which contains the VCID
      value and a message ID through the newly established VC to the
      node B.

   3. The node A establishes an association between the outgoing label
      (VPI/VCI) for the VC and the VCID value.

   4. The node B receives the message from the VC and establishes an
      association between the VCID in the message and the incoming
      label(VPI/VCI) for the VC.  Until the node B receives the LDP
      Request message, the node B discards any packet received over the
      VC other than the VCID PROPOSE message.

   5. The node B sends an ACK message to the node A.  This message
      contains the same VCID and message ID as specified in the received
      message.  This message is sent through the VC for LDP.

   6. When node A receives the ACK message, it checks whether the VCID
      and the message ID in the message are the same as the registered
      ones.  If they are the same, node A regards that node B has
      established the association between the VC and VCID.  Otherwise,
      the message is ignored.  If the node A does not receive the ACK
      message with the expected message ID and VCID during a given
      period, the node A resends the VCID PROPOSE message to the node B.

   7. After receiving the proposer ACK message, the node A sends an LDP
      REQUEST message to the node B.  It contains the message ID used
      for VCID PROPOSE.  When the node B receives the LDP REQUEST
      message, it regards that the node A has received the ACK
      correctly.  The message exchange using VCID PROPOSE, VCID ACK, and
      LDP REQUEST messages constitutes a 3-way handshake.  The 3-way
      handshake mechanism is required since the transmission of VCID
      PROPOSE message is unreliable.  Once the 3-way handshake
      completes, the node B ignores all VCID PROPOSE messages received
      over the VC.  The node B sends an LDP Mapping message, which
      contains the VCID value in the label TLV.

       Node A           Node B
         |                |
         |--------------->|     VCID PROPOSE
         |                |
         |<---------------|     VCID ACK
         |                |
         |--------------->|     LDP Label Request
         |                |
         |<---------------|     LDP Label Mapping

3.1.2 Inband notification for point-to-multipoint VC

   Current LDP specification does not support multicast.  But the VCID
   notification procedure is defined for future use.  VCID notification
   is performed by sending a control message through the VC to be used
   as an LSP.  The upstream node assigns the VCID value.  The procedure
   by which it notifies the downstream node of that value is given
   below.  The procedure is used when a new VC is created or a new leaf
   is added to the VC.

   First, the procedure for establishing the first VC is described.

   1. The upstream node assigns a VCID value for the VC.  When the VCID
      value is already assigned to a VC, it is used for VCID.

   2. The upstream node sends a message which contains the VCID value
      and a message ID through the VC used for an LSP.  This message is
      transferred to all leaf nodes.

   3. The upstream node establishes an association between the outgoing
      label for the VC and the VCID value.

   4. When the downstream nodes receiving the message already received
      the LDP REQUEST message for the VC, the received message is
      discarded.  Otherwise, the downstream nodes establish an
      association between the VCID in the message and the VC from which
      the message is received.

   5. The downstream nodes send an ACK message to the upstream node.

   6. After the upstream node receives the ACK messages, the upstream
      node and the downstream nodes share the VCID.  The upstream node
      sends the LDP REQUEST message in order to make a 3-way handshake.

       Upstream        Downstream 1   Downstream 2
         |                |               |
         |-----------+--->|               |   VCID PROPOSE
         |           +------------------->|
         |                |               |
         |<---------------|               |
         |  VCID ACK      |               |
         |<-------------------------------|   VCID ACK

   Second, the procedure for adding a leaf to the existing point-to-
   multipoint VC is described.

   0. The upstream node adds the downstream node, using the ATM
      signaling.

   1. The VCID value which already assigned to the VC is used.

   2. The upstream node sends a message which contains the VCID value
      and a message ID through the VC used for an LSP.  This message is
      transferred to all leaf nodes.

   3. When the downstream nodes receiving the message already received
      the LDP REQUEST message for the VC, the received message is
      discarded.  Otherwise, the downstream nodes establish an
      association between the VCID in the message and the VC from which
      the message is received.

   4. After the upstream node receives the ACK messages, the upstream
      node and the downstream nodes share the VCID.  The upstream node
      sends the LDP REQUEST message in order to make a 3-way handshake.

3.2 Outband Notification using a small-sized field

   This method can be applied when a VC is established using an ATM
   signaling message and the message has a field which is not large
   enough to carry a VCID value.

   SETUP message of the ATM Forum UNI 3.1/4.0 has a 7-bit mandatory
   field for the user.  This is a user specific field in the Layer 3
   protocol field in the BLLI IE (Broadband Low Layer Information
   Information Element).

   The BLLI value is used as a temporary identifier for a VC during a
   VCID notification procedure.  This mechanism is defined as "Outband
   Notification using a small-sized field".  The BLLI value of a new VC
   must not be assigned to other VCs during the procedure to avoid
   identifier conflict.  When the association among the BLLI value, a
   VCID value, and the corresponding VC is established, the BLLI value
   can be reused for a new VC.  VCID values can be assigned
   independently from BLLI values.

       Node A           Node B
         |                |
         |--------------->|     ATM Signaling with BLLI
         |<---------------|
         |                |
         |--------------->|     VCID PROPOSE with BLLI
         |                |
         |<---------------|     VCID ACK
         |                |
         |--------------->|     LDP Label Request
         |                |
         |<---------------|     LDP Label Mapping

   A point-to-multipoint VC can also be established using ADD_PARTY of
   the ATM Forum Signaling.  ADD_PARTY adds a new VC leaf to an existing
   VC or an existing VC tree.  In this procedure, the BLLI value of
   ADD_PARTY has to be the same value as that used to establish the
   first point-to-point VC of the tree.  The same BLLI value can be used
   in different VC trees only when these VC trees can not add a leaf at
   the same time.  As a result, the BLLI value used in the signaling
   must be determined by the root node of the multicast tree.

   [note]
      BLLI value is unique at the sender node.  But BLLI value is not
      unique at the receiver node because multiple sender nodes may
      allocate the same BLLI value.  So, the receiver node must
      recognize BLLI value and the sender address.  ATM Signaling
      messages (SETUP and ADD_PARTY) carry both the BLLI and the sender
      ATM address.  The receiver node can realize which node sends the
      BLLI message.

3.2.1 Outband notification using a small-sized field for
      point-to-point VC

   This subsection describes procedures for establishing a VC and for
   notification of its VCID between neighboring LSRs for unicast
   traffic.

   The procedure employed when the upstream LSR assigns a VCID is as
   follows.

   1. An upstream LSR establishes a VC to the downstream LSR using ATM
      signaling and supplies a value in the BLLI field that it is not
      currently using for any other (incomplete) VCID notification
      transaction with this peer.

   2. The upstream LSR sends the VCID PROPOSE message through the VC for
      LDP to notify the downstream LSR of the association between the
      BLLI and VCID values.

   3. The downstream LSR establishes the association between the VC with
      the BLLI value and the VCID and sends an ACK message to the
      upstream LSR.

   4. After the upstream LSR receives the ACK message, it establishes
      the association between the VC and the VCID.  The VC is ready to
      be used.  At this time the BLLI value employed in this transaction
      is free for reuse.

   5. After VCID notification, the upstream node sends the LDP REQUEST
      message to the downstream node.  The downstream node sends the LDP
      mapping message, which contains the VCID value in the label TLV of
      LDP.

3.2.2 Outband notification using a small-sized field
      for point-to-multipoint VC

   This subsection describes procedures for establishing the first VC
   for a multicast tree and for adding a new VC leaf to an existing VC
   tree including the notification of its VCID for a multicast stream
   using point-to-multipoint VCs.

   In this procedure, an upstream LSR determines both the VCID and BLLI
   value in the multicast case.  The reason that the BLLI value is
   determined by an upstream LSR is described above.

   First, the procedure for establishing the first VC is described.

   1. An upstream LSR establishes a VC by the ATM Forum Signaling
      between the downstream LSR with a unique BLLI value at this time.

   2. The upstream LSR notifies the downstream LSR of a paired BLLI
      value and VCID using a message dedicated for this purpose.

   3. The downstream LSR establishes the association between the VC with
      the BLLI value and the VCID and sends an ACK message to the
      upstream LSR.  If the VCID is used by some other VC between the
      upstream and downstream LSRs, the old VC is discarded.

   4. After the upstream LSR receives the ACK message, the VC is ready
      to be used and the BLLI value can be used for another VC.

   Second, the procedure for adding a leaf to the existing point-to-
   multipoint VC is described.

   1. The upstream LSR establishes a VC by the ATM Forum Signaling
      between its downstream LSR with the BLLI value that was used
      during the first signaling procedure.  If another VC is using the
      BLLI value at the same time, the upstream waits for the completion
      of the signaling procedure that is using this BLLI value.

   2. Go to step 2 of the procedure for the first VC.

3.3 Outband notification

   This method can be applied when a VC is established using a ATM
   signaling message and the message has a field (e.g., GIT [GIT]) which
   is large enough to carry a VCID value.  Message format is described
   in [GIT].  After the VCID notification, the node A sends the LDP
   request message is sent to the node B.  Then, the node B sends the
   LDP mapping message to the node A.

       Node A           Node B
         |                |
         |--------------->|   ATM signaling with VCID
         |<---------------|
         |                |
         |--------------->|     LDP Label Request
         |                |
         |<---------------|     LDP Label Mapping

4 VPID Notification Procedure

   The approach that is used for the VCID notification procedure is also
   applicable to share the same identifier between both ends for a VP.
   VPID notification procedure is defined for this purpose.

   A distinct VPID notification procedure is performed for each
   direction of each VP.

   After the VPID notification is finished for a VP, a VCID of a VC in
   the VP is constructed with the VPID(MSB) and VCI(LSB) of the VC.  The
   VCID can be used by LDP without performing VCID notification
   procedure.  The message sequence is given below.

   1. An upstream node sends the VPID PROPOSE message. In the case of
      bidirectional label switched VC, both the upstream and downstream
      nodes use VCI=33.  In the case of unidirectional label switched
      VC, the node which has larger LDP Identifier uses VCI=33 and the
      other node uses VCI=34.  Note that VCI=32, which is used for
      unlabeled packet transfer, is not used for VPID notification
      procedure so that the same encapsulation method can be applied for
      both VPID procedure and inband VCID procedure.

   2. The downstream node sends the VPID ACK message.

   3. The upstream node sends the LDP Label Request message.

   4. The downstream node sends the LDP Label Mapping message.

5 VCID Message Format

5.1 VCID Messages

   An LDP VCID message consists of the LDP [LDP] fixed header followed
   by one or more TLV.  A VCID PROPOSE inband message and a VPID PROPOSE
   message are sent as a null encapsulation packet through a VC to be
   used as an LSP.  There is only the label stack header before the LDP
   VCID PDU.  A label value in the label stack entry [ENCAPS] for the
   VCID PROPOSE inband message and the VPID PROPOSE message are 4.
   Other messages are sent as TCP packets.  This is the same as LDP.

   The VCID message type field is as follows:

         VCID Propose inband Message  = 0x0501
         VCID Propose Message         = 0x0502
         VCID ACK Message             = 0x0503
         VCID NACK Message            = 0x0504
         VPID Propose inband Message  = 0x0505
         VPID ACK Message             = 0x0506
         VPID NACK Message            = 0x0507

5.1.1 VCID Propose inband Message

   This message is sent as a null encapsulation packet with LDP header
   and label stack header through a VC to be used as an LSP.  The label
   value is 4.  The reserved label value is required because the
   downstream node may receive this message after receiving the LDP
   Label Request message in the case of point-to-multipoint VC.  The
   downstream node must distinguish the VCID PROPOSE message from other
   messages and ignore the VCID PROPOSE message when the node already
   received the LDP Label Request message for the VC.

    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|VCID Inband Propose (0x0501) |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Message ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Label TLV                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Optional Parameters                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message Id
     Four octet integer used to identify this message.

   Label TLV
     Label TLV contains VCID value.  Type of label TLV is VCID(0x0203).

5.1.2 VCID Propose Message

   An LSR uses the VCID PROPOSE message for the VCID notification
   procedure of the outband notification using a small-sized field.
   This message is sent through the VC for the LDP.

    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|  VCID Propose (0x0502)      |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Message ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Label TLV                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Temporary ID TLV                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Optional Parameters                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message ID
     Four octet integer used to identify this message.

   Label TLV
     Label TLV contains VCID value.  Type of label TLV is VCID(0x0203).

   Temporary ID TLV
     The value carried in the user specific field in the layer 3
     protocol field in the BLLI ID in the ATM Forum UNI 3.1/4.0 Type of
     label TLV is VCID temporary ID(0x0702).

5.1.3 VCID ACK Message

   An LSR send the VCID ACK message when the LSR accepts the VCID
   PROPOSE message.

    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|  VCID ACK     (0x0503)      |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Message ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Label TLV                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           VCID Message ID                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Optional Parameters                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message ID
     Four octet integer used to identify this message.

   Label TLV
     The label TLV contains the VCID value of the received VCID PROPOSE
     message.  Type of label TLV is VCID(0x0203).

   VCID Message ID
     This value is the same as that of received VCID PROPOSE message.

5.1.4 VCID NACK Message

   An LSR send the VCID NACK message when the LSR does not accept the
   VCID PROPOSE message.

    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|  VCID NACK    (0x0504)      |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Message ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Label TLV                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           VCID Message ID                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Optional Parameters                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message ID
     Four octet integer used to identify this message.

   Label TLV
     The label TLV contains the VCID value of the received VCID PROPOSE
     message.  Type of label TLV is VCID(0x0203).

   VCID Message ID
     This value is the same as that of received VCID PROPOSE message.

5.1.5 VPID Propose inband Message

   This message is sent as a null encapsulation packet with LDP header
   and label stack header through a VC to be used as an LSP.  The label
   value is 4.  The downstream node must distinguish the VPID PROPOSE
   message from other messages and ignore the VPID PROPOSE message when
   the node already received the LDP Label Request message for the VC.

    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|VPID Inband Propose (0x0505) |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Message ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           VPID TLV                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Optional Parameters                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message Id
     Four octet integer used to identify this message.

   VPID TLV
     VPID TLV contains VPID value.  Type of label TLV is VPID(0x0703).

5.1.6 VPID ACK Message

   An LSR send the VPID ACK message when the LSR accepts the VPID
   PROPOSE message.

    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|  VPID ACK     (0x0506)      |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Message ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           VPID TLV                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           VCID Message ID                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Optional Parameters                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message ID
     Four octet integer used to identify this message.

   VPID TLV
     The VPID TLV contains the VPID value of the received VPID PROPOSE
     message.

   VCID Message ID
     This value is the same as that of received VCID PROPOSE message.

5.1.7 VPID NACK Message

   An LSR send the VPID NACK message when the LSR accepts the VPID
   PROPOSE message.

    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|  VPID NACK    (0x0507)      |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Message ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           VPID TLV                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           VCID Message ID                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Optional Parameters                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message ID
     Four octet integer used to identify this message.

   VPID TLV
     The VPID TLV contains the VPID value of the received VPID PROPOSE
     message.

   VCID Message ID
     This value is the same as that of received VCID PROPOSE message.

5.2 Objects

5.2.1 VCID Label TLV

   An LSR uses VCID Label TLV to encode labels for use on the link which
   does not have the same data link label at both ends of a VC.

    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|VCID Label   (0x0203)      |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              VCID                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   VCID
     This is 4 byte VCID value.

5.2.2 VCID Message ID 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|VCID Message ID(0x0701)    |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       VCID Message ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   VCID Message ID
     This is 4 byte VCID Message ID

5.2.3 VCID Temporary ID TLV

   An LSR uses the VCID temporary ID TLV for the VCID notification
   procedure of the outband notification using a small-sized field.

    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| VCID Temporary ID (0x0702)|          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Temporary ID |
   +-+-+-+-+-+-+-+-+

   Temporary ID:
     The value carried in the user specific field in the layer 3
     protocol field in the BLLI ID in the ATM Forum UNI 3.1/4.0

5.2.4 VPID Label TLV

   An LSR uses VPID TLV for the VPID notification procedure.

    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|   VPID      (0x0703)      |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            VPID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   VPID
     This is 2 byte VPID value.

Security Considerations

   This document does not introduce new security issues other than those
   present in the LDP and may use the same mechanisms proposed for this
   technology.

Acknowledgments

   The authors would like to acknowledge the valuable technical comments
   of Yoshihiro Ohba, Shigeo Matsuzawa, Akiyoshi Mogi, Muneyoshi Suzuki,
   George Swallow and members of the LAST-WG of the WIDE Project.

References

   [LDP]    Andersson, L., Doolan, P., Feldman, N., Fredette, A. and B.
            Thomas, "LDP Specification", RFC 3036, January 2001.

   [GIT]    Suzuki, M., "The Assignment of the Information Field and
            Protocol Identifier in the Q.2941 Generic Identifier and
            Q.2957 User-to-user Signaling for the Internet Protocol",
            RFC 3033, January 2001.

   [ENCAPS] Rosen, E., Viswanathan, A. and R. Callon, "MPLS Label Stack
            Encoding", RFC 3032, January 2001.

Authors' Addresses

   Ken-ichi Nagami
   Computer & Network Development Center, Toshiba Corporation,
   1, Toshiba-cho, Fuchu-shi,
   Tokyo, 183-8511, Japan

   Phone: +81-42-333-2884
   EMail: ken.nagami@toshiba.co.jp


   Noritoshi Demizu
   WaterSprings.ORG
   1-6-11-501, Honjo, Sumida-ku, Tokyo, 130-0004, Japan

   EMail: demizu@dd.iij4u.or.jp


   Hiroshi Esaki
   Computer Center, University of Tokyo,
   2-11-16 Yayoi, Bunkyo-ku,
   Tokyo, 113-8658, Japan

   Phone: +81-3-3812-1111
   EMail: hiroshi@wide.ad.jp


   Yasuhiro Katsube
   Computer & Network Development Center, Toshiba Corporation,
   1, Toshiba-cho, Fuchu-shi,
   Tokyo, 183-8511, Japan

   Phone: +81-42-333-2844
   EMail: yasuhiro.katsube@toshiba.co.jp


   Paul Doolan
   Ennovate Networks
   60 Codman Hill Road
   Boxborough, MA

   Phone: 978-263-2002 x103
   EMail: pdoolan@ennovatenetworks.com

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