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

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12

Internet Engineering Task Force                                  H. Chen
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                           March 5, 2012
Expires: September 6, 2012


The Applicability of the PCE to Computing Protection and Recovery Paths
              for Single Domain and Multi-Domain Networks
             draft-chen-pce-protection-applicability-00.txt

Abstract

   The Path Computation Element (PCE) provides path computation
   functions in support of traffic engineering in Multiprotocol Label
   Switching (MPLS) and Generalized MPLS (GMPLS) networks.

   A link or node failure can significantly impact network services in
   large-scale networks.  Therefore it is important to ensure the
   survivability of large scale networks which consist of various
   connections provided over multiple interconnected networks with
   varying technologies.

   This document examines the applicability of the PCE architecture,
   protocols, and procedures for computing protection paths and
   restoration services, for single and multi-domain networks.

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 September 6, 2012.

Copyright Notice

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




Chen                    Expires September 6, 2012               [Page 1]


Internet-Draft     Applicability of PCE to Protection         March 2012


   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.  Domains  . . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.1.  Inter-domain LSPs  . . . . . . . . . . . . . . . . . .  4
     1.2.  Recovery . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.4.  Conventions used in this document  . . . . . . . . . . . .  5
   2.  Path Computation Element Architecture Considerations . . . . .  5
     2.1.  Online Path Computation  . . . . . . . . . . . . . . . . .  5
     2.2.  Offline Path Computation . . . . . . . . . . . . . . . . .  5
   3.  Protection Service Traffic Engineering . . . . . . . . . . . .  6
     3.1.  Path Computation . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Bandwidth Reservation  . . . . . . . . . . . . . . . . . .  6
     3.3.  Disjoint Path  . . . . . . . . . . . . . . . . . . . . . .  6
     3.4.  Service Preemption . . . . . . . . . . . . . . . . . . . .  6
     3.5.  Share Risk Link Groups . . . . . . . . . . . . . . . . . .  6
     3.6.  Multi-Homing . . . . . . . . . . . . . . . . . . . . . . .  6
       3.6.1.  Ingress and Egress Protection  . . . . . . . . . . . .  7
   4.  Packet Protection Applications . . . . . . . . . . . . . . . .  7
     4.1.  Single Domain Service Protection . . . . . . . . . . . . .  7
     4.2.  Multi-domain Service Protection  . . . . . . . . . . . . .  8
     4.3.  Backup Path Computation  . . . . . . . . . . . . . . . . .  8
     4.4.  Fast Reroute (FRR) Path Computation  . . . . . . . . . . .  8
     4.5.  Point-to-Multipoint Path Protection  . . . . . . . . . . .  8
   5.  Optical Protection Applications  . . . . . . . . . . . . . . .  9
     5.1.  ASON Applicability . . . . . . . . . . . . . . . . . . . .  9
     5.2.  Multi-domain Restoration . . . . . . . . . . . . . . . . .  9
   6.  Path and Service Protection Gaps . . . . . . . . . . . . . . .  9
   7.  Manageability Considerations . . . . . . . . . . . . . . . . .  9
   8.  Security Requirements  . . . . . . . . . . . . . . . . . . . .  9
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   10. Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . .  9
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     11.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10



Chen                    Expires September 6, 2012               [Page 2]


Internet-Draft     Applicability of PCE to Protection         March 2012


1.  Introduction

   Network survivability remains a major concern for network operators
   and service providers, particularly as expanding applications such as
   private and Public Cloud drive increasingly more traffic across
   longer ranges, to a wider number of users.  A variety of well-known
   pre-planned protection and post-fault recovery schemes have been
   developed for IP, MPLS and GMPLS networks.

   The Path Computation Element (PCE) [RFC4655] can be used to perform
   complex path computation in large single domain, multi-domain and
   multi-layered networks.  The PCE can also be used to compute a
   variety of restoration and protection paths and services.

   This document examines the applicability of the PCE architecture,
   protocols, and protocol extensions for computing protection paths and
   restoration services.

1.1.  Domains

   A domain can be defined as a separate administrative, geographic, or
   switching environment within the network.  A domain may be further
   defined as a zone of routing or computational ability.  Under these
   definitions a domain might be categorized as an Antonymous System
   (AS) or an Interior Gateway Protocol (IGP) area (as per [RFC4726] and
   [RFC4655]), or specific switching environment.

   In the context of GMPLS, a particularly important example of a domain
   is the Automatically Switched Optical Network (ASON) subnetwork
   [G-8080].  In this case, computation of an end-to-end path requires
   the selection of nodes and links within a parent domain where some
   nodes may, in fact, be subnetworks.  Furthermore, a domain might be
   an ASON routing area [G-7715].  A PCE may perform the path
   computation function of an ASON routing controller as described in
   [G-7715-2].

   It is assumed that the PCE architecture should be applied to small
   inter-domain topologies and not to solve route computation issues
   across large groups of domains, I.E. the entire Internet.

   Most existing protocol mechanisms for network survivability have
   focused on single-domain scenarios.  Multi-domain scenarios are much
   more complex and challenging as domain topology information is
   typically not shared outside each specific domain.

   Therefore multi-domain survivability is a key requirement for today's
   complex networks.  It is important to develop more adaptive multi-
   domain recovery solutions for various failure scenarios.



Chen                    Expires September 6, 2012               [Page 3]


Internet-Draft     Applicability of PCE to Protection         March 2012


1.1.1.  Inter-domain LSPs

   Three signaling options are defined for setting up an inter-area or
   inter-AS LSP [RFC4726]:

   - Contiguous LSP

   - Stitched LSP

   - Nested LSP

   Three signaling options are defined for setting up an inter-area or
   inter-AS LSP [RFC4726]:

1.2.  Recovery

   Typically traffic-engineered networks such as MPLS-TE and GMPLS, use
   protection and recovery mechanisms based on the pre-established use
   of a packet or optical LSP and/or the availability of spare resources
   and the network topology.

1.3.  Terminology

   ABR: IGP Area Border Router, a router that is attached to more than
   one IGP area.

   ASBR: Autonomous System Border Router, a router used to connect
   together ASs of a different or the same Service Provider via one or
   more inter-AS links.

   CSPF: Constrained Shortest Path First.

   Inter-area TE LSP: A TE LSP whose path transits through two or more
   IGP areas.

   Inter-AS MPLS TE LSP: A TE LSP whose path transits through two or
   more ASs or sub-ASs (BGP confederations.

   SRLG: Shared Risk Link Group.

   TED: Traffic Engineering Database, which contains the topology and
   resource information of the domain.  The TED may be fed by Interior
   Gateway Protocol (IGP) extensions or potentially by other means.

   This document also uses the terminology defined in [RFC4655] and
   [RFC5440].





Chen                    Expires September 6, 2012               [Page 4]


Internet-Draft     Applicability of PCE to Protection         March 2012


1.4.  Conventions used in this document

   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 RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS.  Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.


2.  Path Computation Element Architecture Considerations

   For the purpose of this document it is assumed that the path
   computation is the sole responsibility of the PCE as per the
   architecture defined in [RFC4655].  When a path is required the Path
   Computation Client (PCC) will send a request to the PCE.  The PCE
   will apply the required constraints and compute a path and return a
   response to the PCC.  In the context of this document it may be
   necessary for the PCE to co-operate with other PCEs in adjacent
   domains (as per BRPC [RFC5441]) or cooperate with the Parent PCE (as
   per [H-PCE]).

   A PCE may be used to compute end-to-end paths across single or
   multiple domains.  Multiple PCEs may be dedicated to each area to
   provide sufficient path computation capacity and redundancy for each
   domain.

   During path computation [RFC5440], a PCC request may contain backup
   LSP requirements in order to setup in the same time the primary and
   backup LSPs.  This request is known as dependent path computations.
   A typical dependent request for a primary and backup service would
   request that the computation assign a set of diverse paths, so both
   services are disjointed from each other.

2.1.  Online Path Computation

   Online path computation is performed on-demand as nodes in the
   network determine that they need to know the paths to use for
   services.

2.2.  Offline Path Computation

   Offline path computation is performed ahead of time, before the LSP
   setup is requested.  That means that it is requested by, or performed
   as part of, a management application.

   This method of computation allows the optimal placement of services



Chen                    Expires September 6, 2012               [Page 5]


Internet-Draft     Applicability of PCE to Protection         March 2012


   and explicit control of services.  A CSP can plan where new
   protection services will be placed ahead of time.  Furthermore by
   computing paths offline specific scenarios can be considered and a
   global view of network resources is available.

   Finally, offline path computation provides a method to compute
   protection paths in the event of a single, or multiple, link
   failures.  This allows the placement of backup services in the event
   of catastrophic network failures.


3.  Protection Service Traffic Engineering

3.1.  Path Computation

   This document describes how the PCE architecture defined in [RFC4655]
   may be utilized to compute protection and recovery paths for critical
   network services.  In the context of this document (inter-domain) it
   may be necessary for the PCE to co-operate with other PCEs in
   adjacent domains (as per BRPC [RFC5441]) or cooperate with the Parent
   PCE (as per [H-PCE]).

3.2.  Bandwidth Reservation

3.3.  Disjoint Path

   Disjoint paths are required for end-to-end protection services.  A
   backup service may be required to be fully disjoint from the primary
   service, link disjoint (allowing common nodes on the paths), or best-
   effort disjoint (allowing shared links or nodes when no other path
   can be found).

3.4.  Service Preemption

3.5.  Share Risk Link Groups

3.6.  Multi-Homing

   Networks constructed from multi-areas or multi-AS environments may
   have multiple interconnect points (multi-homing).  End-to-end path
   computations may need to use different interconnect points to avoid
   single point failures disrupting primary and backup services.

   Domain and path diversity may also be required when computing end-to-
   end paths.  Domain diversity should facilitate the selection of paths
   that share ingress and egress domains, but do not share transit
   domains.  Therefore, there must be a method allowing the inclusion or
   exclusion of specific domains when computing end-to-end paths.



Chen                    Expires September 6, 2012               [Page 6]


Internet-Draft     Applicability of PCE to Protection         March 2012


3.6.1.  Ingress and Egress Protection

   An end-to-end primary service carried by a primary TE LSP from a
   primary ingress node to a primary egress node may need to be
   protected against the failures in the ingress and the egress.  In
   this case, a backup ingress and a backup egress are required, which
   are different from the primary ingress and the primary egress
   respectively.  The backup ingress should be in the same domain as the
   primary ingress, and the backup egress should be in the same domain
   as the primary egress.

   A source of the service traffic may be sent to both the primary
   ingress and the backup ingress (dual-homing).  The source may not be
   in the same domain as the primary ingress and the backup ingress.
   When the primary ingress fails, the service traffic is delivered
   through the backup ingress.

   A receiver of the service traffic may be connected to both the
   primary egress and the backup egress (dual-homing).  The receiver may
   not be in the same domain as the primary egress and the backup
   egress.  When the primary egress fails, the receiver gets the service
   traffic from the backup egress.


4.  Packet Protection Applications

   Network survivability is a key objective for CSPs, particularly as
   expanding revenue services (cloud and data center applications) are
   increasing exponentially.

   Pre-fault paths are pre-computed and protection resources are
   reserved a priory for rapid recovery.  In the event of a network
   failure on the primary path, the traffic is fast switched to the
   backup path.  These pre-provisioned mechanisms are capable of
   ensuring protection against single link failures.

   Post-fault restoration schemes are reactive and require a reactive
   routing procedure to set up new working paths in the event of a
   failure.  Post fault restoration can significantly impact network
   services as they are typically impacted by longer restoration delays
   and cannot guarantee recovery of a service.  However, they are much
   more network resource efficient and are capable of handling multi-
   failure situations.

4.1.  Single Domain Service Protection

   A variety of pre-planned protection and post-fault restoration
   recovery schemes are available for single domain MPLS and GMPLS



Chen                    Expires September 6, 2012               [Page 7]


Internet-Draft     Applicability of PCE to Protection         March 2012


   networks, these include:

   o Path Recovery

   o Path Segment Recovery

   o Local Recovery (Fast Reroute)

4.2.  Multi-domain Service Protection

   Typically network survivability has focused on single-domain
   scenarios.  By contrast, broader multi-domain scenarios are much more
   challenging as no single entity has a global view of topology
   information.  As a result, multi-domain survivability is very
   important.

   A PCE may be used to compute end-to-end paths across multi-domain
   environments using a per-domain path computation technique [RFC5152].
   The so called backward recursive path computation (BRPC) mechanism
   [RFC5441] defines a PCE-based path computation procedure to compute
   inter-domain constrained LSPs.

4.3.  Backup Path Computation

   A PCE can be used to compute backup paths in the context of fast
   reroute protection of TE LSPs.  In this model, all backup TE LSPs
   protecting a given facility are computed in a coordinated manner by a
   PCE.  This allows complete bandwidth sharing between backup tunnels
   protecting independent elements, while avoiding any extensions to TE
   LSP signaling.  Both centralized and distributed computation models
   are applicable.  In the distributed case each LSR can be a PCE to
   compute the paths of backup tunnels to protect against the failure of
   adjacent network links or nodes.

4.4.  Fast Reroute (FRR) Path Computation

   [RFC409] extends RSVP-TE to establish backup LSPs for the local
   repair of LSP tunnels.  This extension allows CSPs to redirect
   traffic onto the backup LSP tunnels in 10s of milliseconds.

   This local repair of the LSP is applicable to explicitly-routed LSPs.
   An FRR repair method is applicable to explicitly-routed LSPs across a
   single domain environment.

4.5.  Point-to-Multipoint Path Protection

   A PCE utilizing the extensions outlined in [RFC6006] (Extensions to
   PCEP for Point-to-Multipoint Traffic Engineering Label Switched



Chen                    Expires September 6, 2012               [Page 8]


Internet-Draft     Applicability of PCE to Protection         March 2012


   Paths), can be used to compute point-to-multipoint (P2MP) paths.

   A PCC requesting path computation for a primary and backup path can
   request that these dependent computations use diverse paths.
   Furthermore, the specification also defines two new options for P2MP
   path dependent computation requests.  The first option allows the PCC
   to request that the PCE should compute a secondary P2MP path tree
   with partial path diversity for specific leaves or a specific source-
   to-leaf (sub-path to the primary P2MP path tree.  The second option,
   allows the PCC to request that partial paths should be link direction
   diverse


5.  Optical Protection Applications

5.1.  ASON Applicability

5.2.  Multi-domain Restoration


6.  Path and Service Protection Gaps


7.  Manageability Considerations

   This document does not describe any specific protocol, protocol
   extensions, or protocol usage, therefore no manageability
   considerations need to be discussed here.


8.  Security Requirements

   This document is informational and does not describe any new specific
   protocol, protocol extensions, or protocol usage.  As such, it
   introduces no new security concerns.


9.  IANA Considerations

   This document makes no requests for IANA action.


10.  Acknowledgement

   The authors would like to thank Daniel King for his valuable
   contributions to this draft.





Chen                    Expires September 6, 2012               [Page 9]


Internet-Draft     Applicability of PCE to Protection         March 2012


11.  References

11.1.  Normative References

11.2.  Informative References

   [RFC3473]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Resource ReserVation Protocol-Traffic
              Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.

   [RFC4090]  Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
              Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              May 2005.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655, August 2006.

   [RFC4726]  Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for
              Inter-Domain Multiprotocol Label Switching Traffic
              Engineering", RFC 4726, November 2006.

   [RFC5152]  Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
              Path Computation Method for Establishing Inter-Domain
              Traffic Engineering (TE) Label Switched Paths (LSPs)",
              RFC 5152, February 2008.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.

   [RFC5441]  Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A
              Backward-Recursive PCE-Based Computation (BRPC) Procedure
              to Compute Shortest Constrained Inter-Domain Traffic
              Engineering Label Switched Paths", RFC 5441, April 2009.

   [RFC6006]  Zhao, Q., King, D., Verhaeghe, F., Takeda, T., Ali, Z.,
              and J. Meuric, "Extensions to the Path Computation Element
              Communication Protocol (PCEP) for Point-to-Multipoint
              Traffic Engineering Label Switched Paths", RFC 6006,
              September 2010.











Chen                    Expires September 6, 2012              [Page 10]


Internet-Draft     Applicability of PCE to Protection         March 2012




   [G-8080]  ITU-T Recommendation G.8080/Y.1304, Architecture for
             the automatically switched optical network (ASON).

   [G-7715]  ITU-T Recommendation G.7715 (2002), Architecture
             and Requirements for the Automatically Switched
             Optical Network (ASON).

   [G-7715-2] ITU-T Recommendation G.7715.2 (2007), ASON routing
             architecture and requirements for remote route query.

   [H-PCE]  King, D. and A. Farrel, "The Application of the Path
            Computation Element Architecture to the Determination
            of a Sequence of Domains in MPLS & GMPLS", July




Author's Address

   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   Email: Huaimochen@huawei.com











































Chen                    Expires September 6, 2012              [Page 11]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/