Subject: RE: PW status TLV Problem - text update

From: Luca Martini <[email-masked]>
Date: Wed, 11 Feb 2004 17:38:22 -0700

Updated text according to comments.

Thanks.
Luca

5.3. Signaling of Pseudo Wire Status

5.3.1. Use of Label Mappings.

   The PEs MUST send PW label mapping messages to their peers as soon as
   the PW is configured and administratively enabled, regardless of the
   CE-facing interface state. The PW label should not be withdrawn
   unless the user administratively configures the CE-facing interface
   down (or the PW configuration is deleted entirely). Using the
   procedures outlined in this section a simple label withdraw method
   MAY also be supported as a primitive means of signaling WP status. It

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   is strongly RECOMMENDED that the PW status signaling procedures below
   be fully implemented. In any case if the Label mapping is not
   available the PW MUST be considered in the down state.

5.3.2. Signaling PW status.

   The PE devices use an LDP TLV to indicate status to their remote
   peers. This PW Status TLV contains more information than the
   alternative simple Label Withdraw message.

   The format of the PW Status 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1|0|     PW Status (0x096A)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Status Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   [ note: TLV type 0x096A as defined in [13] pending IANA allocation ]

   Where the status code is a 4 octet bit field is specified in the PW
   IANA Allocations document [13].

   Each bit in the status code field can be set individually to indicate
   more then a single failure at once. Each fault can be cleared by
   sending an appropriate status message with the respective bit
   cleared. The presence of the lowest bit (PW Not Forwarding) acts only
   as a generic failure indication when there is a link-down event for
   which none of the other bits apply.

   The Status TLV is transported to the remote PW peer via the LDP
   notification message. The general format of the Notification Message
   is:

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   Notification (0x0001)     |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Message ID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Status (TLV)                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      PW Status TLV                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 PWId FEC or Generalized ID FEC                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Status TLV status code is set to 0x00000028 "PW status", to
   indicate that PW status follows. Since this notification does not
   refer to any particular message the Message Id, and Message Type
   fields are set to 0.  [ note: Status Code 0x00000028 as defined in
   [13] pending IANA allocation ] A more detailed diagram is shown in
   Appendix B.

   The PW FEC TLV SHOULD not include the interface parameters as they
   are ignored in the context of this message. When a PE's CE-facing
   interface encounters an error, use of the PW status message allows
   the PE to send a single status message, using a PW FEC TLV with only
   the group ID set, to denote this change in status for all affected PW
   connections.

   As mentioned above the Group ID field can be used to send a status
   notification for all PWs associated with a particular group ID. This
   procedure is OPTIONAL, and if it is implemented the LDP Notification
   message should be as follows: the PW information length field is set
   to 0, the PW ID field is not present, and the interface parameters
   field is not present. For the purpose of this document this is called
   the "wild card PW status notification procedure", and all PEs
   implementing this design are REQUIRED to accept such a notification
   message, but are not required to send it.

5.3.3. Pseudowire Status Negotiation Procedures

   When a PW is first set up the PEs MUST attempt to negotiate the usage
   of the PW status TLV. This is accomplished as follows:  A PE that
   supports the PW Status TLV MUST include it the initial label mapping
   signaling immediately following label mapping TLV, the PW FEC, and
   the interface parameters field. The PW Status TLV will then be used
   for the lifetime of the Pseudowire. This is shown in the following

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   diagram:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                 PWId FEC or Generalized ID FEC                +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Interface parameters                    |
   |                              "                                |
   |                              "                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|0| Generic Label (0x0200)    |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Label                                                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1|0|     PW Status (0x0???)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Status Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   If PW status TLV is sent immediately following the label mapping TLV
   in the initial PW FEC Message, but the remote PE corresponding FEC
   advertisement does not include a PW status TLV, or the remote PE does
   not support the PW Status TLV and the PW will revert to the label
   withdraw method to signal PW status. Note that if the PW Status TLV
   is not supported, by the remote peer, it will automatically be
   ignored, since the LDP ignore bit is set. The PW Status TLV,
   therefore, will not be present in the corresponding FEC advertisement
   from the remote LDP peer resulting in exactly the above behavior.

   If the PW Status TLV is not present immediately following the label
   mapping TLV in the initial PW FEC Message received by a PE, then the
   PW Status TLV will not be used and both PEs supporting the pseudowire
   will revert to the label withdraw procedure for signaling status
   changes.

   If the negotiation process results in the usage of the PW status TLV,
   then the actual PW status is determined by the PW status TLV that was
   sent within the initial PW label mapping. Subsequent updates of PW
   status are conveyed through the notification message

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