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Versions: 00 01 02 03 draft-ietf-mpls-smp-requirements

Network Working Group                                      Y. Weingarten
Intended status: Informational                                 S. Aldrin
Expires: May 23, 2013                                Huawei Technologies
                                                                  P. Pan
                                                                 J. Ryoo
                                                               G. Mirsky
                                                       November 19, 2012

              Requirements for MPLS Shared Mesh Protection


   This document presents the basic network objectives for the behavior
   of shared mesh protection (SMP) not based on control-plane support.
   This is an expansion of the basic requirements presented in the MPLS
   Transport Profile Requirements (RFC5654) and MPLS Transport Profile
   Survivability Framework (RFC6372) documents.  This document should be
   used as a basis for the definition of the mechanism that would be
   used to implement SMP for MPLS-TP data paths, in networks that do not
   employ a control plane for their operation.

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
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   This Internet-Draft will expire on May 23, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Protection or Restoration  . . . . . . . . . . . . . . . .  4
     1.2.  Scope of document  . . . . . . . . . . . . . . . . . . . .  4
       1.2.1.  Relationship to MPLS-TP  . . . . . . . . . . . . . . .  4
     1.3.  Contributing Authors . . . . . . . . . . . . . . . . . . .  5
   2.  Terminology and Notation . . . . . . . . . . . . . . . . . . .  5
     2.1.  Acronyms . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  SMP Architecture . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Coordination of resources  . . . . . . . . . . . . . . . .  6
   4.  SMP Network Objectives . . . . . . . . . . . . . . . . . . . .  7
     4.1.  Configuration and resource reservation . . . . . . . . . .  7
       4.1.1.  Checking resource availability . . . . . . . . . . . .  7
     4.2.  Control plane or data plane  . . . . . . . . . . . . . . .  7
     4.3.  Multiple triggers  . . . . . . . . . . . . . . . . . . . .  8
     4.4.  Notification . . . . . . . . . . . . . . . . . . . . . . .  9
     4.5.  Protection switching time  . . . . . . . . . . . . . . . .  9
     4.6.  Timers . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   5.  Managability Considerations  . . . . . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

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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.  The connections, that may be between neighboring
   nodes, i.e. spanning a single physical link, or spanning a path of
   several nodes, 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 (SLA) with their customers.

   MPLS provides control-plane tools to support various survivability
   schemes (Editor's note - add references).  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 criss-cross the mesh, it is possible to conserve 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 allocated and used by
   both the working and protection paths.  Applying 1:1 protection
   requires that all of the resources are allocated, 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, there is a limitation in 1:n
   protection architectures - that all of the n+1 paths must have
   identical endpoints.

   As described in [RFC6372] Shared Mesh Protection (SMP) supports a
   form of sharing protection resources, while providing protection for
   multiple data paths that may not have common endpoints and do not
   share common points of failure.  It should be noted that some
   protection resources may not be shared by multiple protection paths,
   while other resources are shared.  The basic configuration for data
   paths that employ SMP is shown in Figure 1.  In this figure, we show
   two working paths [ABCDE] and [VWXYZ] that are protected employing
   1:1 linear protection by protection paths [APQRE] and [VPQRZ]
   respectively.  The segment [PQR] and all of its protection resources
   are shared by both of the protection paths.

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                 \                 /
                  \               /
                   \             /
                   /             \
                  /               \
                 /                 \

                     Figure 1: Basic SMP architecture

1.1.  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 reserved at the time of path creation.  However, the full
   allocation 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.

1.2.  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.  There are existing
   control-plane solutions for SMP within MPLS, however we address those
   networks that for some reason, e.g. service provider preferences or
   limitations, do not employ a full control plane operation, or require
   service restoration faster than achievable with control plane

   The network objectives will also address possible additional
   restrictions of the behavior of SMP in statically configured operator
   networks.  Definition of logic and specific protocol messaging is out
   of scope of this document.

1.2.1.  Relationship to MPLS-TP

   While some of the restrictions presented by this framework originate
   from the considerations of transport networks, there is no real
   constraint of the information presented here being applied to general
   MPLS networks, and not necessarily as part of the Transport Profile

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   of MPLS.

1.3.  Contributing Authors

   David Allan, Daniel King, Taesik Cheung

2.  Terminology and Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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 draft uses the following acronyms:

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

3.  SMP Architecture

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

                 \            /    /    \
                  \          M ---/--    \
                   \             /   \    \
                   /|      \     \     \    \
                  / F---G---H    J--K---L    \
                 /                            \

                 Figure 2: Larger sample SMP architecture

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   Consider the network presented in Figure 2.  There are five working
   paths - [ABCDE], [MDEN], [FGH], [JKL], and [VWXYZ].  Each of these
   has a corresponding protection path - [APQRE] (p1), [MSTN] (p2),
   [FPQH] (p3), [JRSL] (p4), and [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 addition, 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 the main feature of the network that defines it as an
   SMP network is the fact that the segment [PQRST] is the union of all
   the shared segments of other protection paths (p1, p2, p3 and p4)
   while being a whole shared segment of one of the protection paths

   In other words, the main feature of an SMP "protection domain" will
   be the segment that is the union of all the shared segments of the
   protection paths.  We can further identify "protection group" as the
   different protection paths that share a common segment.  For example,
   referring to Figure 2, we have the following protection groups - {p1,
   p3, p5} for [PQ], {p1, p5} for [QR], {p4, p5} for [RS], {p2, p5} for

   Typical deployment of SMP would require various network planning
   activities.  These would include:

   o  Identification of key services that require protection, and
      determining the number of working and protection paths.

   o  Reviewing network topology to determine which working or
      protection paths are required to be disjointed 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

3.1.  Coordination of resources

   When a protection switch is triggered by any fault condition or
   operator command, the SMP network must perform two operations almost
   simultaneously - switch data traffic over to a protection path and
   verify that the shared resources are allocated for this protection
   path.  The allocation of resources is dependent upon their
   availability at each of the shared segments.

   When the reserved resources of the shared segments are allocated for
   a particular protection path, there may not be sufficient resources

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   available for an additional protection path.  This then implies that
   if an additional working path triggers a protection switch, the
   allocation of the resources may fail and MUST be treated as described
   below in Section 4.3.  In order to optimize the operation of the
   allocation and preparing for cases of multiple working path failures,
   the allocation of the shared resources SHALL be coordinated between
   the different working paths in the SMP network.

4.  SMP Network Objectives

4.1.  Configuration and resource reservation

   SMP is a survivability mechanism that is based on pre-configuration
   of the network working paths and the corresponding protection paths.
   This configuration may be based on either a control protocol or
   static configuration by the management system.  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.

   As opposed to the case of simple linear protection, where the
   relationship between the working and protection paths is defined, the
   resources for the protection path may be fully committed for the
   unshared portions of the protection path.  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.  On the shared segments, the protection
   resources may be reserved but would not be allocated until requested
   as part of a protection switch.

4.1.1.  Checking resource availability

   When a working path identifies a protection switching trigger it MUST
   verify that the necessary protection resources are available on the
   protection path.  The resources may not be available because they
   have been allocated to the protection of a higher priority working
   path, as described above.

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].  In fact, implementations for SMP with
   GMPLS exist and the general principles of its operation are well
   known, if not fully documented.

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   There are, however, operators, in particular in the transport sector,
   that do not operate their MPLS networks under the control of a
   control plane and require the ability of performing SMP protection
   while utilizing data-plane tools for coordination of the protection
   switching.  This requirement is emphasized in different areas of
   [RFC5654] for MPLS-TP environments.  Therefore, it is imperative that
   it be possible to perform all of the coordination needed for SMP via
   data plane operations.

4.3.  Multiple triggers

   If more than one working path is triggering a protection switch 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, for those networks that support
   multiplexing packets over the shared segments.  For those networks,
   in particular for networks that support the requirements in [RFC5654]
   [and in particular support for requirement 58], that require the
   exclusive use of the protection resources, the following behavior
   SHOULD be supported:

   o  Relative priority MAY be assigned to each of the working paths
      that share a common protection segment

   o  Resources of the shared segments SHALL be allocated 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
      allocated on a first come first served basis.  Tie-breaking rules
      SHALL be defined by the SMP process.

   o  If the protection resources are currently in use by a protection
      path, whose working path has a lower priority, resources SHALL be
      allocated to the path with higher priority.  Traffic with lower
      priority MAY use available resources or MAY be interrupted.

   o  When trigerred, protection switching action SHOULD be initiated
      immediately to minimize service interruption time.  If the
      protection resources are already allocated to a higher priority
      protection path the protection switching MAY not be performed.

   o  Once a protection path occupies the resource of a shared segments
      successfully, 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.

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

   o  During preemption, if there is an oversubscription of resources
      protected traffic SHOULD be treated as defined in [RFC5712] or

4.4.  Notification

   When a working path identifies a trigger for implementing a
   switchover to the protection path, it SHOULD attempt to switchover
   the traffic to the protection path and requesting the allocation of
   the resources for this protected traffic.  If the necessary shared
   resources are in use by a protection path of higher priority or are
   unavailable to be allocated to the protection path, a notification
   SHALL be sent to both endpoints of the requesting working path and
   the switchover MAY not be completed.

   Similarly, if preemption is supported and as a result of the
   allocation of resources to a different working path that triggered a
   protection switch, the resources currently allocated for a particular
   working path are being preempted then a notification SHALL be sent to
   the endpoints of the working path whose traffic is being preempted
   indicating that the resources are being preempted.

4.5.  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 is exclusive of 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 4.3.  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 SMP process.  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

4.6.  Timers

   In order to prevent multiple switching actions for a single switching
   trigger, SMP SHOULD be controlled a hold-off timer that would allow
   lower level mechanisms to complete their switching actions before

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   invoking SMP protection actions.

   In addition, 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.  Managability Considerations

   To be added in future version.

6.  Security Considerations

   To be added in future version.

7.  IANA Considerations

   This document makes no request of IANA.

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

8.  Acknowledgements


9.  Normative References

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

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

   [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.

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

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

   [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.

   [RFC5712]  Meyer, M. and JP. Vasseur, "Recovery (Protection and
              Restoration) Terminology for GMPLS", RFC 5712,
              January 2010.

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

Authors' Addresses

   Yaacov Weingarten
   34 Hagefen St.
   Karnei Shomron,   4485500

   Email: wyaacov@gmail.com

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

   Email: aldrin.ietf@gmail.com

   Ping Pan

   Email: ppan@infinera.com

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   Jeong-dong Ryoo
   161 Gajeong
   Yuseong, Daejeon  305-700
   South Korea

   Email: ryoo@etri.re.kr

   Greg Mirsky

   Email: gregory.mirsky@ericsson.com

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