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Network Working Group                                          A. Takacs
Internet-Draft                                               B. Tremblay
Intended status: Standards Track                                Ericsson
Expires: January 14, 2009                                  July 13, 2008


  GMPLS RSVP-TE recovery extension for data plane initiated reversion
                   draft-takacs-ccamp-revertive-ps-01

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Copyright Notice

   Copyright (C) The IETF Trust (2008).














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Abstract

   RSVP-TE recovery extensions are specified in [RFC4872] and [RFC4873].
   Currently these extensions cannot signal request for revertive
   protection to the remote endpoint.  This document defines a new bit
   to signal this request and two new fields to specify a wait-to-
   restore and hold-off intervals.












































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Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  PROTECTION object extension  . . . . . . . . . . . . . . . . .  6
   3.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 13


































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1.  Introduction

   Reversion refers to the process of moving normal traffic back to the
   original working LSP after the failure is cleared and the path is
   repaired [RFC4426][RFC4427][RFC4872].  Reversion is desirable since
   the protection path may not be optimal from a routing and resource
   consumption point of view, additionally, moving traffic back to the
   working LSP allows the protection resources to be used to protect
   other LSPs.  On the other hand, reversion requires that the working
   resources remain allocated during failure.  The operator needs to
   have the choice between revertive and non-revertive protection to
   balance the pros and cons in a given situation.

   [RFC4426] and [RFC4872] describes control plane signalling procedures
   for reversion.  This signaling can be used to initiate the actual
   reversion in the data plane; or simply to synchronise control plane
   states after data plane actions.  This latter case, when
   independently from the control plane, data plane mechanisms
   autonomously initiate reversion is not detailed further in the
   documents.

   [RFC4426] and [RFC4872] assumed that signalling the revertive
   property of protection is not needed between protection endpoints.
   This assumption holds for uni- and bidirectional LSPs in the
   following cases.

   o  The control plane is responsible to execute reversion and trigger
      data plane switch-over.

   o  In the case of data plane initiated reversion there is a dedicated
      protocol for protection switching (e.g., Automatic Protection
      Switching (APS)) synchronising the switch-over of the data plane
      endpoints.

   In these cases, only one side: the ingress LER needs to be provided
   with information about the revertive property of protection.  Hence,
   there is no need to signal any information in RSVP-TE to the remote
   endpoint.

   However, GMPLS may be applied in a scenario where the data plane
   autonomously executes reversion but it has no mechanism to
   communicate the revertive property of protection between the
   endpoints.  Such an example is protection switching of bidirectional
   connections in Ethernet PBB-TE [IEEE-PBBTE] (currently under
   standardisation in IEEE).  In this case revertiveness needs to be
   signalled by RSVP-TE during LSP establishment to properly setup the
   remote data plane endpoint.




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   In order that traffic is not switched back and fort between worker
   and protection LSPs during transients, a wait to restore (WTR) timer
   is usually applied delaying the reversion until the recovered path is
   considered stable again.  Although WTR intervals may be pre-
   configured, it may be beneficial to signal the desired WTR value as
   well.

   There is another timer not yet supported by RSVP-TE recovery
   extensions.  The Hold-off (HOFF) time is applied to protection
   switching to allow lower layer mechanisms to recover from the failure
   before switching to the protection path.  Adding the HOFF timer may
   be also considered when extending RSVP-TE recovery signalling.
   Applying different HOFF intervals to LSPs is motivated when the
   protection capability of the underlying layer varies from LSP to LSP.
   Further, the GMPLS extensions for multi-layer/multi-region networks
   may also reveal the need for more flexible configuration of
   protection switching timers.


































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2.  PROTECTION object extension

   In [RFC4872] and [RFC4873] the PROTECTION object is specified to
   support end-to-end and segment recovery.  Next we discuss how new
   fields for HOFF timer and revertive protection with WTR timer can be
   introduced.

   Often hold-off and WTR intervals are pre-configured in network
   elements and the same default value is used for all the LSPs.  In
   this case, there is no need to signal these parameters, only a new
   bit (V) needs to be added to the PROTECTION object to signal that
   revertive protection is requested.

   The PROTECTION object defined in [RFC4872] and amended in [RFC4873]
   is depicted bellow with the proposed placement of the new V bit.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |S|P|N|O|V| Reserved| LSP Flags |      Reserved     | Link Flags|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |I|R|    Reserved   | Seg.Flags |           Reserved            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           1) First alternative with a new revertive protection bit.

   V - Revertive bit, when set the protection is to be revertive, and if
   supported the data plane should be configured to autonomously execute
   reversion.

   Alternatively, when instead of a default value the WTR time is to be
   set independently for each LSP, a new field needs to be defined.  A
   default WTR value can be used to signal that no reversion is desired.
   Hence, no new bit is needed to select revertive protection.  This
   alternative is depicted 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |S|P|N|O|Res|  WTR  | LSP Flags |      Reserved     | Link Flags|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |I|R|    Reserved   | Seg.Flags |           Reserved            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   2) Second alternative with new WTR field.

   WTR - Wait to Restore, it specifies the WTR delay before reversion.




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   In the general case, if both WTR and HOFF intervals should be set
   independently for each LSP, two new fields need to be defined.  To
   fit the size of the two fields the last 16 bits of the PROTECTION
   object needs to be utilised.  This is depicted 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |S|P|N|O| Reserved  | LSP Flags |      Reserved     | Link Flags|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |I|R|    Reserved   | Seg.Flags | Resv.   |  WTR  |    HOFF     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            3) Third alternative with new WTR and HOFF fields.

   WTR - Wait to Restore, it specifies the WTR delay before reversion.

   HOFF - Hold-off, it specifies the HOFF delay before switching to the
   protection path.
































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3.  IANA Considerations

   TBD.
















































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4.  Security Considerations

   This document introduces no new security issues.  The considerations
   in [RFC4872] and [RFC4873] apply.















































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5.  Acknowledgements

   The authors would like to thank Francesco Fondelli.
















































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6.  References

   [IEEE-PBBTE]
              "IEEE 802.1Qay Draft Standard for Provider Backbone
              Bridging Traffic Engineering",  work in progress.

   [RFC4426]  "Generalized Multi-Protocol Label Switching (GMPLS)
              Recovery Functional Specification", RFC 4426, March 2006.

   [RFC4427]  "Recovery (Protection and Restoration) Terminology for
              Generalized Multi-Protocol Label Switching (GMPLS)",
              RFC 4427, March 2006.

   [RFC4872]  "RSVP-TE Extensions in Support of End-to-End Generalized
              Multi-Protocol Label Switching (GMPLS) Recovery",
              RFC 4872, May 2007.

   [RFC4873]  "GMPLS Segment Recovery", RFC 4873, May 2007.

































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Authors' Addresses

   Attila Takacs
   Ericsson
   Laborc u. 1.
   Budapest,   1037
   Hungary

   Email: attila.takacs@ericsson.com


   Benoit Tremblay
   Ericsson
   8400 Decarie.
   Montreal, Quebec  H4P 2N2
   Canada

   Email: benoit.c.tremblay@ericsson.com

































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Full Copyright Statement

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