PCE                                                              XF. Lin
Internet-Draft                                           ZTE Corporation
Intended status: Informational                                shg. Huang
Expires: July 6, 2013                                              X. Li
                                                                J. Zhang
                                                                M. Zhang
                                                                HX. Wang
                                                                    BUPT
                                                         January 2, 2013


   Path Computation Element (PCE) Extensions for Link State Conflict
           Avoidance Mechanism in Optical Transport Networks
                draft-huangshg-pce-conflict-avoidance-01

Abstract

   This document proposes a PCE based link state conflict avoidance
   mechanism.  Path Computation Element (PCE) can compute a network path
   or route based on the information stored in Traffic Engineering
   Database (TED) and TED collects the link resources information
   through the OSPF-TE protocol.  The proposed conflict avoidance
   mechanism gives each link two state which respectively represents the
   resource in this link is changed or not.  The extended OSPF-TE
   protocol will also flood the link state information when it floods
   the link resources information.  PCE will add the link state to the
   calculated path when it returns the calculated path to Path
   Computation Clients (PCC).  When the RSVP-TE protocol reserves the
   resource along the calculated path, it will compare the link state
   stored in the calculated path with the link state stored in the
   local.  If the link state between the calculated path and the local
   is inconsistent then the RSVP-TE protocol will stop the resource
   reservation process, release the reserved resource and promote the
   OSPF-TE protocol to flood the Link resources information immediately.

Status of this Memo

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   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   time.  It is inappropriate to use Internet-Drafts as reference



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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 6, 2013.

Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  Conventions Used in This Document . . . . . . . . . . . . . . . 5
   3.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Applicability of Link State Conflict Avoidance Mechanism
       in Optical Transport  . . . . . . . . . . . . . . . . . . . . . 5
     4.1.  Two-value link state  . . . . . . . . . . . . . . . . . . . 6
     4.2.  Path Computation Request and Path Computation Reply . . . . 7
     4.3.  RSVP-TE Process . . . . . . . . . . . . . . . . . . . . . . 7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8





































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1.  Introduction

   With the development in large scale optical transport network, the
   calculation of optimal route becomes complicated and unrealistic
   under the distributed optical network of multi-layers and multi-
   domains.  Path Computation Element (PCE) which is capable of
   computing a network path or route based on a network graph, and of
   applying computational constraints has effectively solved this issue.

   [RFC4655] specifies the architecture for a Path Computation Element
   (PCE)-based mode.  It discusses PCE-based implementations including
   composite, external, and multiple PCE path computation.  Furthermore,
   it discusses architectural considerations including centralized
   computation, distributed computation, synchronization, PCE discovery
   and load balancing, detection of PCE liveness, communication between
   Path Computation Clients (PCCs) and the PCE (PCC-PCE communication)
   and PCE-PCE communication, Traffic Engineering Database (TED)
   synchronization, stateful and stateless PCEs, monitoring, policy and
   confidentiality and evaluation metrics.

   [RFC5440] specifies the Path Computation Element (PCE) Communication
   Protocol (PCEP) for communications between a Path Computation Client
   (PCC) and a PCE, or between two PCEs.  Such interactions include path
   computation requests and path computation replies as well as
   notifications of specific states related to the use of a PCE in the
   context of Multiprotocol Label Switching (MPLS) and Generalized MPLS
   (GMPLS) Traffic Engineering.  PCEP is designed to be flexible and
   extensible so as to easily allow for the addition of further messages
   and objects.

   [RFC5557] provides a set of requirements and PCEP extensions in
   support of concurrent path computation applications.  A concurrent
   path computation is a path computation application where a set of TE
   paths are computed concurrently in order to efficiently utilize
   network resources.  The computation method involved with a concurrent
   path computation is referred to as "global concurrent optimization"
   in this document.  Appropriate computation algorithms to perform this
   type of optimization are out of the scope of this document.

   PCE system structure characteristics include: PCE is compatible with
   existing MPLS/GMPLS agreement.  PCE is compatible with existing MPLS/
   GMPLS network operation mode, including management level.  PCE uses a
   single, signaling protocol and structure, suitable for different
   network environment, such as inner domain, between domains, and
   between different operators, etc.  PCE allows operators or equipment
   manufacturers use different routing algorithms, based on complex
   traffic engineering parameters and strategy calculation routing; and
   has the flexible system structures.  PCE can work with nets element



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   equipment together, also can be in a single server implementation.
   When the PCC and the PCE is not in the same physical location, they
   use PCEP protocol and BRPC algorithm to realize multi-domain path
   requests and path calculation.


2.  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 [RFC2119].


3.  Terminologies

   PCC: Path Computation Client.

   PCE: Path Computation Element.

   TED: Traffic Engineering Database.

   PCEP: The PCE communication Protocol.


4.  Applicability of Link State Conflict Avoidance Mechanism in Optical
    Transport

   Once a request has been presented to a PCE, it chooses the proper
   route within the network based on the resource information in TED.
   The TED gathers the information related to the current topology and
   resource usage in the network by continuous interaction with the
   OSPF-TE protocol.  When the PCE has chosen the route for a router
   demand, the corresponding LSP will be setup using RSVP-TE protocol,
   which will take care of performing node-by-node admission control and
   actual resource allocation.  OSPF-TE advertises the change of local
   resource allocation status to all other TED by sending a Link State
   Update message containing a special kind of Link State Advertisement
   object called opaque LSA.  The LSU message is distributed to all LSRs
   using the OSPF flooding procedure.

   In order to avoid that the massive information flooding is executed
   for each minimal change, some flooding reduction mechanisms are used,
   so that the origination rate of OSPF-TE LSU messages can be reduced.
   But the flooding reduction mechanisms may cause that the resource
   information stored in the TED cannot be updated in real time.  A
   potential solution would be to advertise a two-value state for each
   local link with little size of packet.  This would require
   implementations to process these two-value state TLVs during the path



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   calculation in PCE.  It need to increase the rate of OSPF-TE Link
   State messages and is anticipated that the Link State messages will
   prove more generally useful.

4.1.  Two-value link state

   Each local link will be given two-value (0,1) link state where
   1represent the resource in local link state have be changed and 0
   represent the resource in local link state have no changed.  The link
   state TLV is as presented in the Fig.1.


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Type                |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                             Value                             |
       //                                                             //
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           LS age              |    Options    |      10       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          1        |                 Instance                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Advertising router                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      LS sequence number                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           LS checksum         |           Length              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+












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        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Length              | Class-Num(36) |  C-Tyoe(1)    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Advertising Router |     Reserved      |     Label Type        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Subchanne l                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                             ...                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Subchanne N                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.2.  Path Computation Request and Path Computation Reply

   Once a PCC has successfully established a PCEP session with one or
   more PCEs, it sends a path computation request to the PCE that
   contains a variety of objects that specify the set of constraints and
   attributes for the path to be computed.  Upon receiving a path
   computation request from a PCC, the PCE triggers a path computation.
   The PCE manages to compute a path that includes the link state
   information.  Then PCE returns the set of computed paths
   (EXPLICIT_ROUTE object) to the requesting PCC.  Note that PCEP
   supports the capability to send link state TLV in the computed path.

4.3.  RSVP-TE Process

   RSVP-TE enables the allocation of resources along the path.  The
   source node adds an EXPLICIT_ROUTE object to the RSVP-TE Path
   message.  The EXPLICIT_ROUTE object specifies the route as a sequence
   of nodes.  When the RSVP-TE reserve the resource in the local link
   then in will compare the link state stored in the calculated path
   with the link state stored in the local.  If the link state between
   the calculated path and the local is inconsistent then the RSVP-TE
   protocol will stop the resource reservation process, release the
   reserved resource and promote the OSPF-TE protocol to flood the Link
   resources information immediately.


5.  Security Considerations

   TBD.







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6.  Acknowledgments

   TBD.


7.  Normative References

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

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

   [RFC4657]  Ash, J. and J. Le Roux, "Path Computation Element (PCE)
              Communication Protocol Generic Requirements", RFC 4657,
              September 2006.

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


Authors' Addresses

   Xuefeng Lin
   ZTE Corporation
   No.16,Huayuan Road,Haidian District
   Beijing  100191
   P.R.China

   Phone: +8615901011821
   Email: lin.xuefeng@zte.com.cn
   URI:   http://www.zte.com.cn/


   Shanguo Huang
   BUPT
   No.10,Xitucheng Road,Haidian District
   Beijing  100876
   P.R.China

   Phone: +8613693578265
   Email: shghuang@bupt.edu.cn
   URI:   http://www.bupt.edu.cn/







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   Xin Li
   BUPT
   No.10,Xitucheng Road,Haidian District
   Beijing  100876
   P.R.China

   Phone: +8613426082735
   Email: xinli@bupt.edu.cn
   URI:   http://www.bupt.edu.cn/


   Jie Zhang
   BUPT
   No.10,Xitucheng Road,Haidian District
   Beijing  100876
   P.R.China

   Phone: +8613911060930
   Email: lgr24@bupt.edu.cn
   URI:   http://www.bupt.edu.cn/


   Min Zhang
   BUPT
   No.10,Xitucheng Road,Haidian District
   Beijing  100876
   P.R.China

   Phone: +8613910621756
   Email: @bupt.edu.cn
   URI:   http://www.bupt.edu.cn/


   Hongxiang Wang
   BUPT
   No.10,Xitucheng Road,Haidian District
   Beijing  100876
   P.R.China

   Phone: +8613683683550
   Email: wanghx@bupt.edu.cn
   URI:   http://www.bupt.edu.cn/









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