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Requirements for MPLS-TP Shared Mesh Protection
draft-ietf-mpls-smp-requirements-05

The information below is for an old version of the document.
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This is an older version of an Internet-Draft that was ultimately published as RFC 7412.
Authors Yaacov Weingarten , Sam Aldrin , Ping Pan , Jeong-dong Ryoo , Greg Mirsky
Last updated 2014-06-09 (Latest revision 2014-05-30)
Replaces draft-weingarten-mpls-smp-requirements
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Send notices to mpls-chairs@tools.ietf.org, draft-ietf-mpls-smp-requirements@tools.ietf.org
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draft-ietf-mpls-smp-requirements-05
Network Working Group                                      Y. Weingarten
INTERNET-DRAFT                                                          
Intended status: Informational                                 S. Aldrin
Expires: November 29, 2014                           Huawei Technologies
                                                                  P. Pan
                                                                Infinera
                                                                 J. Ryoo
                                                                    ETRI
                                                               G. Mirsky
                                                                Ericsson
                                                            May 28, 2014

            Requirements for MPLS-TP Shared Mesh Protection
                draft-ietf-mpls-smp-requirements-05.txt

Abstract

   This document presents the basic network objectives for the behavior
   of shared mesh protection (SMP) which are not based on control plane
   support. This is an expansion of the basic requirements presented in
   RFC 5654 "Requirements for the Transport Profile of MPLS" and RFC
   6372 "MPLS Transport Profile (MPLS-TP) Survivability Framework". 
   This document is to be used as a basis for the definition of any
   mechanism that would be used to implement SMP for MPLS-TP data paths,
   in networks that delegate executive action for resiliency to the data
   plane.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 29, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
 

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology and Notation . . . . . . . . . . . . . . . . . . .  3
     2.1.  Acronyms . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.2.  Terms defined in this document . . . . . . . . . . . . . .  4
   3. Shared Mesh Protection Reference Model  . . . . . . . . . . . .  4
     3.1.  Protection or Restoration  . . . . . . . . . . . . . . . .  4
     3.2.  Scope of document  . . . . . . . . . . . . . . . . . . . .  5
       3.2.1.  Relationship to MPLS . . . . . . . . . . . . . . . . .  5
   4.  SMP Architecture . . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Coordination of resources  . . . . . . . . . . . . . . . .  7
     4.2.  Control plane or data plane  . . . . . . . . . . . . . . .  8
   5.  SMP Network Objectives . . . . . . . . . . . . . . . . . . . .  8
     5.1.  Resource reservation and coordination  . . . . . . . . . .  8
       5.1.1.  Checking resource availability for multiple 
               protection paths . . . . . . . . . . . . . . . . . . .  9
     5.2.  Multiple triggers  . . . . . . . . . . . . . . . . . . . .  9
     5.3.  Notification . . . . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Revertive protection switching . . . . . . . . . . . . . . 10
     5.5.  Protection switching time  . . . . . . . . . . . . . . . . 11
     5.6.  Timers . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.7.  Communicating information and channel  . . . . . . . . . . 11
   6.  Manageability Considerations . . . . . . . . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   10.  Normative References  . . . . . . . . . . . . . . . . . . . . 12
   11. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 13
   12. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13

 

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1.  Introduction

   MPLS transport networks can be characterized as being a network of
   connections between nodes within a mesh of nodes and the links
   between them.  A connection may be between neighboring nodes (i.e.
   spanning a single physical link) or between non-adjacent nodes
   (spanning a path over multiple nodes). The connections in a network
   constitute the Label Switched Paths (LSP) that transport packets
   between the endpoints of these paths. The survivability of these
   connections, as described in [RFC6372], is a critical aspect for
   various service providers that are bound by Service Level Agreements
   (SLAs) with their customers.

   MPLS provides control plane tools to support various survivability
   schemes, some of which are identified in [RFC4426]. In addition,
   recent efforts in the IETF have started providing for data plane
   tools to address aspects of data protection. In particular, [RFC6378]
   defines a set of triggers and coordination protocol for 1:1 and 1+1
   linear protection of p2p paths.

   When considering a full-mesh network and the protection of different
   paths that traverse the mesh, it is possible to provide an acceptable
   level of protection while conserving the amount of protection
   resources needed to protect the different data paths.  As pointed out
   in [RFC6372] and [RFC4428], applying 1+1 linear protection requires
   that resources are committed for use by both the working and
   protection paths.  Applying 1:1 protection requires that the same
   resources are committed, but allows the resources of the protection
   path to be utilized for pre-emptible extra traffic.  Extending this
   to 1:n or m:n protection allows the resources of the protection path
   to be shared in the protection of several working paths. However, 1:n
   or m:n protection architecture is limited by the restriction that all
   of the n+1 or m+n paths must have the same endpoints. 

2.  Terminology and Notation

   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 [RFC2119].

   The terminology used in this document is based on the terminology
   defined in the MPLS-TP Survivability Framework document [RFC6372]
   which in-turn is based on [RFC4427].

2.1.  Acronyms

   This document uses the following acronyms:

 

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   LSP  Label Switched Path
   SLA  Service Level Agreement
   SMP  Shared Mesh Protection
   SRLG Shared Risk Link Group

2.2.  Terms defined in this document
   This document defines the following terms:

   SMP Protection Group: the set of different protection paths that
   share a common segment. 

3. Shared Mesh Protection Reference Model

   As described in [RFC6372] Shared Mesh Protection (SMP) supports the
   sharing of  protection resources, while providing protection for
   multiple working paths that need not have common endpoints and do not
   share common points of failure. Note that some protection resources
   may be shared, while some others may not be. An example of data paths
   that employ SMP is shown in Figure 1.  It shows two working paths
   <ABCDE> and <VWXYZ> that are protected employing 1:1 linear
   protection by protection paths <APQRE> and <VPQRZ> respectively. The
   two protection paths that traverse segment <PQR> share the protection
   resources on this segment.

                A----B----C----D----E
                 \                 /
                  \               /
                   \             /
                    P-----Q-----R
                   /             \
                  /               \
                 /                 \
                V----W----X----Y----Z

          Figure 1: Basic SMP architecture

3.1.  Protection or Restoration

   [RFC6372], based upon the definitions in [RFC4427], differentiates
   between "protection" and "restoration" dependent upon the dynamism of
   the resource allocation. In SMP, the resources of the protection
   paths are planned at the time of path creation.  However, the
   commitment of the resources, at least for the shared segments, will
   only be finalized when the protection path is actually activated.
   Therefore, for the purists - regarding the terminology - SMP lies
   somewhere between protection and restoration.
 

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3.2.  Scope of document

   [RFC5654] establishes that MPLS-TP SHOULD support shared protection
   (Requirement 68) and that MPLS-TP MUST support sharing of protection
   resources (Requirement 69). This document presents the network
   objectives and a framework for applying SMP within an MPLS network,
   without the use of control plane protocols. Although there are
   existing control plane solutions for SMP within MPLS, a data plane
   solution is required for networks that do not employ a full control
   plane operation for some reason (e.g. service provider preferences or
   limitations), or require service restoration faster than is
   achievable with control plane mechanisms.

   The network objectives will also address possible additional
   restrictions of the behavior of SMP in networks that delegate
   executive action for resiliency to the data plane. Definition of
   logic and specific protocol messaging is out of scope of this
   document.

3.2.1.  Relationship to MPLS

   While some of the restrictions presented by this document originate
   from the properties of transport networks, nothing prevents the
   information presented here being applied to MPLS networks outside the
   scope of the Transport Profile of MPLS.

4.  SMP Architecture

   Figure 1 shows a very basic configuration of working and protection
   paths that may employ SMP.  We may consider a slightly more complex
   configuration, such as the one in Figure 2 in order to illustrate
   characteristics of a mesh network that implements SMP.

                A----B----C----D----E---N
                 \            /    /    \
                  \          M ---/--    \
                   \             /   \    \
                    P-----Q-----R-----S----T
                   /|      \     \     \    \
                  / F---G---H    J--K---L    \
                 /                            \
                V------W-------X-------Y-------Z

          Figure 2: Larger sample SMP architecture

   Consider the network presented in Figure 2. There are five working
   paths

 

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      -  <ABCDE>

      -  <MDEN>

      -  <FGH>

      -  <JKL>

      -  <VWXYZ>

   Each of these has a corresponding protection path 

      -  <APQRE> (p1)

      -  <MSTN> (p2)

      -  <FPQH> (p3)

      -  <JRSL> (p4)

      -  <VPQRSTZ> (p5)

   The following segments are shared by two or more of the protection
   paths - <PQ> is shared by p1, p3, and p5, <QR> is shared by p1 and
   p5, <RS> is shared by p4 and p5, and <ST> is shared by p2 and p5. In
   Figure 2, we have the following SMP Protection Groups - {p1, p3, p5}
   for <PQ>, {p1, p5} for <QR>, {p4, p5} for <RS>, {p2, p5} for <ST>.

   We assume that the available protection resources for these shared
   segments are not sufficient to support the complete traffic capacity
   of the respective working paths that may use the protection paths. We
   can further observe that with a method of coordinating sharing and
   preemption there is no co-routing constraints on shared components at
   the segment level.

   The use of preemption in the network is typically a business or
   policy decision such that when protection resources are contended,
   priority can be applied to determine to which parties the protection
   resources are committed.

   As opposed to the case of simple linear protection, where the
   relationship between the working and protection paths is defined and
   the resources for the protection path are fully committed, the
   protection path in the case of SMP consists of segments that are
   dedicated to the protection of the related working path and also
   segments that are shared with other protection paths such that
 

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   typically the protection resources are oversubscribed to support
   working paths that do not share common points of failure. What is
   required is a preemption mechanism to implement business priority
   when multiple failure scenarios occur. As such, the protection
   resources may be planned but would not be committed until requested
   and resolved in relation to other members of the SMP Protection Group
   as part of a protection switchover.

   [RFC5712] defines two types of preemption that can be considered for
   how the resources of SMP Protection Groups, are shared. These are
   "soft preemption" whereby traffic of lower priority paths is degraded
   and "hard preemption" where traffic of lower priority paths is
   completely blocked. "Hard Preemption" requires the programming of
   selectors at the ingress of each shared segment to specify which
   backup path has the highest priority when committing protection
   resources, the others being preempted. When any protection mechanism
   whereby the protection end point may have a choice of protection
   paths (e.g. n:1 or m:n) is deployed the shared segment selectors
   require coordination with the protection end points as well.

   Typical deployment of services that use SMP requires various network
   planning activities. These include:

   o  Determining the number of working and protection paths required to
      achieve resiliency targets for the service.

   o  Reviewing network topology to determine which working or
      protection paths are required to be disjoint from each other, and
      exclude specified resources such as links, nodes, or shared risk
      link groups (SRLGs).

   o  Determining the size (bandwidth) of the shared resource

4.1.  Coordination of resources

   When a protection switch is triggered, the SMP network performs two
   operations simultaneously - switch data traffic over to a protection
   path and commit the associated resources. The commitment of resources
   is dependent upon their availability at each of the shared segments.

   When the reserved resources of the shared segments are committed to a
   particular protection path, there may not be sufficient resources
   available for an additional protection path.  This then implies that
   if another working path of the SMP domain triggers a protection
   switch, the commitment of the resources may fail. In order to
   optimize the operation of the commitment and preparing for cases of
   multiple working paths failing, the commitment of the shared
   resources are be coordinated between the different working paths in
 

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   the SMP network.

4.2.  Control plane or data plane

   As stated in both [RFC6372] and [RFC4428], full control of SMP
   including both configuration and the coordination of the protection
   switching is potentially very complex. Therefore, it is suggested
   that this be carried out under the control of a dynamic control plane
   similar to GMPLS [RFC3945]. Implementations for SMP with GMPLS exist
   and the general principles of its operation are well known, if not
   fully documented.

   However, there are operators, in particular in the transport sector,
   that do not operate their MPLS-TP networks under the control of a
   control plane or for other reasons have delegated executive action
   for resilience to the data plane, and require the ability to utilize
   SMP protection. For such networks it is imperative that it be
   possible to perform all required coordination of selectors and end
   points for SMP via data plane operations.

5.  SMP Network Objectives

5.1.  Resource reservation and coordination

   SMP is based on pre-configuration of the working paths and the
   corresponding protection paths. This configuration may be based on
   either a control protocol or static configuration by the management
   system. However, even when the configuration is performed by a
   control protocol, e.g.  Generalized MPLS (GMPLS), the control
   protocol SHOULD NOT be used as the primary resilience mechanism.

   The protection relationship between the working and protection paths
   SHOULD be configured and the shared segments of the protection path
   MUST be identified prior to use of the protection paths. Relative
   priority for working paths to be used to resolve contention for
   protection path usage by multiple working paths MAY also be specified
   ahead of time.

   When a protection switch is triggered by any fault condition or
   operator command, the SMP network MUST perform two operations
   simultaneously - switch data traffic over to a protection path and
   commit the associated resources. 

   In the case of multiple working paths failing, the commitment of the
   shared resources SHALL be coordinated between the different working
   paths in the SMP network.

 

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5.1.1.  Checking resource availability for multiple protection paths

   In a hard-preemption scenario, when an end point identifies a
   protection switching trigger and has more than one potential action
   (e.g. n:1 protection) it MUST verify that the necessary protection
   resources are available on the selected protection path. The
   resources may not be available because they already have been
   committed to the protection of, for example, a higher priority
   working path.

5.2.  Multiple triggers

   If more than one working path is triggering a protection switch such
   that a protection segment is oversubscribed, there are different
   possible actions that the SMP network may apply. The basic MPLS
   action MAY allow all of the protection paths to share the resources
   of the shared segments (soft-preemption), for networks that support
   multiplexing packets over the shared segments.

   There are networks that require the exclusive use of the protection
   resources (i.e. hard preemption). These include networks that support
   the requirements in [RFC5654], and in particular support requirement
   58. For such networks, the following requirements apply:

   o  Relative priority MAY be assigned to each of the working paths of
      an SMP domain. If the priority is not assigned, the working paths
      are assumed to have equal priority.

   o  Resources of the shared segments SHALL be committed to the
      protection path according to the highest priority amongst those
      requesting use of the resources.

   o  If multiple protection paths of equal priority are requesting
      allocation of the shared resources, the resources SHOULD be
      committed on a first come first served basis. Tie-breaking rules
      SHALL be defined in scope of an SMP domain.

   o  If the protection resources are committed to a protection path,
      whose working path has a lower priority, resources required for
      the higher priority path SHALL be committed to the higher priority
      path. Traffic with lower priority MAY use available resources or
      MAY be interrupted.

   o  When triggered, protection switching action SHOULD be initiated
      immediately to minimize service interruption time.

   o  If the protection resources are already committed to a higher
      priority protection path the protection switching SHALL NOT be
 

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      performed.

   o  Once resources of shared segments have been successfully committed
      to a protection path, the traffic on that protection path SHALL
      NOT be interrupted by any protection traffic whose priority is
      equal or lower than the protecting path currently in-use.

   o  During preemption, shared segment resources MAY be used by both
      existing traffic (that is being preempted) and higher priority
      traffic.

   o  During preemption, if there is an over-subscription of resources
      protected traffic SHOULD be treated as defined in [RFC5712] or
      [RFC3209].

5.3.  Notification

   When a working path endpoint has a protection switch triggered, it
   SHOULD attempt to switch the traffic to the protection path and
   request the commitment of protection resources. If the necessary
   shared resources are unavailable to be committed to the protection
   path, the endpoints of the requesting working path SHALL be notified
   of protection switchover failure, and switchover MAY not be
   completed.

   Similarly, if preemption is supported and the resources currently
   committed for a particular working path are being preempted then the
   endpoints of the affected working path whose traffic is being
   preempted SHALL be notified that the resources are being preempted.

5.4.  Revertive protection switching

   When the working path detects that the condition that triggered the
   protection switch has cleared, it is possible to either revert to
   using the working path resources or continue to utilize the
   protection resources. Continuing the use of protection resources
   allows the operator to delay the disruption of service caused by the
   switchover until periods of lighter traffic. The switchover would
   need to be performed via an explicit operator command unless the
   protection resources are preempted by a higher priority fault. Hence,
   both automatic and manual revertive behaviors MUST be supported for
   hard-preemption in an SMP domain. Normally the network should revert
   to use of the working path resources in order to clear the protection
   resources for protection of other path triggers. However, the
   protocol MUST support non-revertive configurations.

 

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5.5.  Protection switching time

   Protection switching time refers to the transfer time (Tt) defined in
   [G.808.1] and recovery switching time defined in [RFC4427], and is
   defined as the interval after a switching trigger is identified until
   the traffic begins to be transmitted on the protection path.  This
   time does not include the time needed to initiate the protection
   switching process after a failure occurred, and the time needed to
   complete preemption of existing traffic on the shared segments as
   described in Section 4.2. The former, which is known as detection and
   correlation time in [RFC4427], is related to the OAM or management
   process, but the latter is related to the actions within an SMP
   domain. Support for a protection switching time of 50ms is dependent
   upon the initial switchover to the protection path, but the
   preemption time SHOULD also be taken into account to minimize total
   service interruption time.

5.6.  Timers

   In order to prevent multiple switching actions for a single switching
   trigger, when there are multiple layers of networks, SMP SHOULD be
   controlled by a hold-off timer that would allow lower layer
   mechanisms to complete their switching actions before invoking SMP
   protection actions.

   In order to prevent an unstable recovering working path from invoking
   intermittent switching operation, SMP SHOULD employ a wait-to-restore
   timer during any reversion switching.

5.7.  Communicating information and channel

   SMP in hard-preemption mode SHOULD include support for communicating
   information to coordinate the use of the shared protection resources
   among multiple working paths.  The message encoding and communication
   channel between the nodes of the shared protection resource and the
   endpoints of the protection path are out of the scope of this
   document.

   SMP in hard-preemption mode SHOULD provide a communication channel,
   along the protection path, between the endpoints of the protection
   path to support fast protection switching.

6.  Manageability Considerations

   The network management architecture and requirements for MPLS-TP are
   specified in [RFC5951].  They derive from the generic specifications
   described in ITU-T G.7710/Y.1701 [G.7710] for transport technologies.
   This document does not introduce any new manageability requirements
 

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   beyond those covered in those documents.

7.  Security Considerations

   General security considerations for MPLS-TP are covered in [RFC5921].
   The security considerations for the generic associated control
   channel are described in [RFC5586]. This document introduces no new
   security considerations beyond those covered in those documents.

8.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

9.  Acknowledgements

   This document is the outcome of discussions on Shared Mesh Protection
   for MPLS-TP. The authors would like to thank all contributors to
   these discussions, and especially Eric Osborne for facilitating them.

10.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., and V.
              Srinivasan, "RSVP-TE: Extensions to RSVP for LSP Tunnels",
              RFC 3209, December 2001.

   [RFC3945]  Mannie, E., "Generalized Multi-Protocol Label Switching
              (GMPLS) Architecture", RFC 3945, Oct 2004.

   [RFC4426]  Lang, J., Rajagopalan, B., and Papadimitriou, D.E. "GMPLS
              Recovery Functional Specification", RFC 4426, March 2006.

   [RFC4427]  Mannie, E. and D. Papadimitriou, "Recovery (Protection and
              Restoration) Terminology for GMPLS", RFC 4427, March 2006.

   [RFC4428]  Mannie, E. and D. Papadimitriou, "Analysis of Generalized
              Multi-Protocol Label Switching (GMPLS)-based Recovery
              Mechanisms (including Protection and Restoration)",
              RFC 4428, March 2006.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., 
              "MPLS Generic Associated Channel", RFC 5586, June 2009.
 

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   [RFC5654]  Niven-Jenkins, B., Nadeau, T., and C. Pignataro,
              "Requirements for the Transport Profile of MPLS",
              RFC 5654, Sept 2009.

   [RFC5712]  Meyer, M. and JP. Vasseur, "MPLS Traffic Engineering Soft
              Preemption", RFC 5712, January 2010.

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, July 2010.

   [RFC5951]  Lam, K., Mansfield, S., and E. Gray, "Network Management
              Requirements for MPLS-based Transport Networks", RFC 5951,
              September 2010.

   [RFC6372]  Sprecher, N. and A. Farrel, "MPLS-TP Survivability
              Framework", RFC 6372, Sept 2011.

   [RFC6378]  Sprecher, N., Bryant, S., Osborne, E., Fulignoli, A., and
              Y. Weingarten, "MPLS-TP Linear Protection", RFC 6378,
              Nov 2011.

   [G.808.1]  ITU, "Generic Protection Switching - Linear trail and
              subnetwork protection", ITU-T G.808.1, Feb 2010.

11. Contributing Authors

   David Allan
   Ericsson
   Email: david.i.allan@ericsson.com

   Daniel King
   Old Dog Consulting
   Email: daniel@olddog.co.uk

   Taesik Cheung
   ETRI
   Email: cheung.taesik@gmail.com

12. Authors' Addresses

   Yaacov Weingarten
   34 Hagefen St.
   Karnei Shomron,   4485500
   Israel

   Email: wyaacov@gmail.com
 

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   Sam Aldrin
   Huawei Technologies
   2330 Central Express Way
   Santa Clara, CA  95951
   United States

   Email: aldrin.ietf@gmail.com

   Ping Pan
   Infinera

   Email: ppan@infinera.com

   Jeong-dong Ryoo
   ETRI
   218 Gajeongro
   Yuseong, Daejeon  305-700
   South Korea

   Email: ryoo@etri.re.kr

   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com

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