[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01

MPLS Working Group                              Dave Allan, Greg Mirsky
Internet Draft                                                 Ericsson
Intended status: Informational
Expires: February 2013
                                                            August 2012


        A framework for the use of SPMEs for shared mesh protection
                       draft-allan-mpls-spme-smp-fmwk-01


Abstract

   Shared mesh protection allows a set of diversely routed paths with
   diverse endpoints to collectively oversubcribe protection resources.
   Under normal conditions no single failure will result in the capacity
   of the associated protection resources to be exhausted.

   When multiple failures occur such that more than one path in the set
   of paths utilizing shared protection resources is affected, the
   necessity arises of pre-empting traffic on the basis of business
   priority rather than application priority.

   This memo describes the use of SPMEs and TC marking as a means of
   indicating business priority for shared mesh protection.

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 RFC2119 [1].

Status of this Memo

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

   Internet-Drafts are working documents of the Internet
   Engineering Task Force (IETF), its areas, and its working
   groups.  Note that other groups may also distribute working
   documents as Internet-Drafts.

   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".



Allan et al.,            Expires February 2013                 [Page 1]


Internet-Draft    draft-allan-mpls-spme-smp-fmwk-01         August 2012


   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 2nd 2011.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   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
   1.1. Authors......................................................3
   2. Conventions used in this document..............................3
   2.1. Terminology..................................................3
   3. Overview.......................................................4
   3.1. Architectural Overview.......................................4
   4. Signalling Implications........................................5
   5. IANA Considerations............................................5
   6. Security Considerations........................................5
   7. References.....................................................6
   7.1. Normative References.........................................6
   7.2. Informative References.......................................6
   8. Authors' Addresses.............................................6











Allan et al.,            Expires February 2013                 [Page 2]


Internet-Draft    draft-allan-mpls-spme-smp-fmwk-01         August 2012


1. Introduction

   Shared mesh protection is described in [2]. A common interpretation
   of the behavior of shared mesh protection emerges from the circuit
   switched world whereby subtending path selectors and selector
   coordination functions support path preemption to ensure that the
   highest priority path needing the protection resources is granted
   ownership of the shared segment, all others being preempted, and such
   functionality can be successfully delegated to dataplane OAM.

   Ultimately this resolves into a business priority decision vs. an
   application priority decision in how customer traffic is handled. The
   packet world is different from the circuit world in that there is no
   guarantee of convenient alignment of resource requirements between
   preempting and preempted paths. Nor in a packet environment is there
   the need to completely preempt all the traffic in a lower priority
   path simply because a higher priority path lays claim to the
   resources. Finally it is useful to obviate the requirement for
   preempting and preemptable traffic to be co-routed.

   This memo proposes the use of SPMEs with the pipe model of TC copying
   as an alternative to the use of path pre-emption, path selectors and
   selector coordination functions for the purposes of implementing
   business policy.

1.1. Authors

David Allan, Greg Mirsky

2. Conventions used in this document

2.1. Terminology

MPLS-TP: MPLS Transport Profile

MPLS-TP LSP: Uni-directional or Bidirectional Label Switch Path
representing a circuit

SMP: Shared Mesh Protection

SPME: Sub-Path Maintenance Entity

TC: Traffic Class

TTL: Time To Live




Allan et al.,            Expires February 2013                 [Page 3]


Internet-Draft    draft-allan-mpls-spme-smp-fmwk-01         August 2012


3. Overview

   Shared mesh protection is described in [2]. A common interpretation
   of the behavior of shared mesh protection emerges from the circuit
   switched world. In that interpretation subtending path selectors and
   selector coordination support path preemption functionality to ensure
   that the highest priority path needing the protection resources is
   the one granted ownership of the shared segment; all others being
   preempted. It also assumes that all paths sharing the protection
   resources conveniently all need exactly the same size pipe.

   In packet transport networks there will frequently not be a
   convenient 1:1 equivalence of the bandwidth requirements of the set
   of transport paths sharing protection resources such that a simple
   pre-emption decision can be made. For example 3 paths: A, B, and C
   sized "n", "n/2" and "n/2" respectively could have a shared segment
   size "3n/2" such that simultaneous failures necessitating the
   activation of any two of the protection paths could be accommodated
   without path preemption. When one ranks A, B and C with a variety of
   priorities and considers all failure combinations a rather large
   matrix of possible required behaviors emerges.

   If one pursues this line of thinking to its logical conclusion, and
   envisions a significant set of paths of diverse sizes and diverse
   priorities, the policy associated with successful path prioritization
   and preemption becomes quite complex, and ensuring multiple selectors
   make timely and of necessity common preemption decisions starts to
   impose network design constraints or require additional coordination
   protocols that severely impact the utility of SMP.

   Further in a packet network there can be a difference in the
   bandwidth reserved and the bandwidth actually used at any given
   instant in time. One consequence is that there is no need to
   completely preempt all the traffic in a lower priority path simply
   because a higher priority path lays a preferential claim to the
   bandwidth.

   To obviate these problems, this memo proposes an alternative to how
   business priority can be implemented for shared mesh protection that
   obviates the need for path preemption and the limitations such an
   approach imposes.

3.1. Architectural Overview

   This memo pre-supposes an operational mode of behavior along the
   lines of the following:



Allan et al.,            Expires February 2013                 [Page 4]


Internet-Draft    draft-allan-mpls-spme-smp-fmwk-01         August 2012


   1) As a matter of network design, specific links (or engineered
      virtual links) are set aside for the purpose of acting as shared
      protection resources. The key attribute of these links is that
      the processing of TC markings will be exclusively for shared
      protection.

   2) The arrangement of the shared protection links can be arbitrary
      such that contiguous domains can be constructed with an arbitrary
      number of ingress and egress points. A set of contiguous
      protection links is known as a protection domain.

   3) Either an apriori or on-demand mesh of SPMEs that connect all
      ingress and egress points in a protection domain is required.
      These are logically forwarding adjacencies for the purposes of
      routing protection paths

   4) The instantiation of protection paths requires the mapping of the
      incoming path at an ingress node for the protection domain to an
      SPME that connects the ingress to the required egress node from
      the domain.

   5) The pipe model of TC copying is used such that the SPME gets the
      TC marking associated with the business priority for the path
      associated with the incoming label value. As the SPME only
      transits resources where the TC marking has been overloaded in
      this fashion business priority does not conflict with application
      requirements.

   6) Admission control for the protection paths transiting the
      protection domain is performed such that the sum of the bandwidth
      for a given business priority does not oversubscribe any links in
      the protected domain, but the sum of the bandwidth for all
      business priorities can. In this way no traffic of the highest
      business priority using the shared mesh pool will be contended.



4. Signalling Implications

   For a future version of this document.

5. IANA Considerations

   No IETF protocols were harmed in the publishing of this memo.

6. Security Considerations

   For a future version of this document.

Allan et al.,            Expires February 2013                 [Page 5]


Internet-Draft    draft-allan-mpls-spme-smp-fmwk-01         August 2012


7. References

7.1. Normative References

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

7.2. Informative References

  [2]   Sprecher, N., et al. "MPLS Transport Profile (MPLS-TP)
        Survivability Framework", RFC 6372, September 2011

8. Authors' Addresses

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

   Greg Mirsky
   Ericsson
   Email: Gregory.mirsky@ericsson.com




























Allan et al.,            Expires February 2013                 [Page 6]


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/