Path Computation Element (PCE) Protocol Extensions for Stateful PCE Usage in GMPLS-controlled Networks

Network Working Group                                        Xian Zhang
Internet-Draft                                                Young Lee
Intended status: Standards Track                            Fatai Zhang
                                                         Ramon Casellas
                                                 Oscar Gonzalez de Dios
                                                         Telefonica I+D

Expires: August 21, 2013                              February 22, 2013

   Path Computation Element (PCE) Protocol Extension for Stateful PCE
                        Usage in GMPLS Networks


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
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   This Internet-Draft will expire on August 21, 2013.

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   The Path Computation Element (PCE) facilitates Traffic Engineering
   (TE) based path calculation in large, multi-domain, multi-region, or
   multi-layer networks. [Stateful-PCE] provides the fundamental PCEP
   extensions needed to support stateful PCE functions, without
   specifying the technology-specific extensions. This memo provides
   extensions required for PCE communication protocol (PCEP) so as to
   enable the usage of a stateful PCE capability in GMPLS networks.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [RFC2119].

Table of Contents

   Table of Contents .............................................. 2
   1. Introduction ................................................ 3
   2. PCEP Extensions ............................................. 3
      2.1. Overview of Requirements................................ 3
      2.2. Stateful PCE Capability Advertisement and Negotiation....4
         2.2.1. PCE Capability Negotiation/Advertisement in Multi-layer
         Networks ................................................. 4
      2.3. LSP Delegation in GMPLS Networks ........................5
      2.4. LSP Synchronization in GMPLS networks ...................6
      2.5. Modification of Existing PCEP Messages and Procedures....8
         2.5.1. Use cases ......................................... 8
         2.5.2. Modification for LSP Re-optimization ...............9
         2.5.3. Modification for Route Exclusion ...................9
      2.6. Additional Error Type and Error Values Defined..........10
   3. IANA Considerations ........................................ 10
   4. Manageability Considerations................................ 10
      4.1. Requirements on Other Protocols and Functional Components11
   5. Security Considerations..................................... 11
   6. Acknowledgement ............................................ 11
   7. References ................................................. 11
      7.1. Normative References................................... 11
      7.2. Informative References................................. 12
   8. Contributors' Address....................................... 12
   Authors' Addresses ............................................ 13

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1. Introduction

   [RFC 4655] presents the architecture of a Path Computation Element
   (PCE)-based model for computing Multiprotocol Label Switching (MPLS)
   and Generalized MPLS (GMPLS) Traffic Engineering Label Switched
   Paths (TE LSPs). To perform such a constrained computation, a PCE
   stores the network topology (i.e., TE links and nodes) and resource
   information (i.e., TE attributes) in its TE Database (TED). To
   request path computation services to a PCE, [RFC 5440] defines the
   PCE Communication Protocol (PCEP) for communications between a Path
   Computation Client (PCC) and a PCE, or between two PCEs. PCEP
   protocol specified in [RFC 5440] mainly focuses on MPLS networks and
   the PCEP extensions needed for GMPLS-controlled networks are
   provided in [PCEP-GMPLS].

   Stateful PCEs are shown to be helpful in many application scenarios,
   in both MPLS and GMPLS networks, as illustrated in [Stateful-APP].
   In order for these applications to able to exploit the capability of
   stateful PCEs, extensions to the PCE communication protocol (i.e.,
   PCEP) are required.

   [Stateful-PCE] provides the fundamental extensions needed for
   stateful PCE to support general functionality, but leaves out the
   specification for technology-specific objects/TLVs. Complementarily,
   this document focuses on the extensions that are necessary in order
   for its deployment in GMPLS-controlled networks.

2. PCEP Extensions

2.1. Overview of Requirements

   This section notes the main functional requirements for PCEP
   extensions to support stateful PCE for use in GMPLS networks, based
   on the description in [Stateful-APP]. Many requirements are common
   across a variety of network types (e.g., MPLS-TE networks and GMPLS
   networks) and the protocol extensions to meet the requirements are
   already described in [Stateful-PCE]. This document does not repeat
   the description of those protocol extensions. Other requirements
   that are also common across a variety of network types do not
   currently have protocol extensions defined in [Stateful-PCE]. In
   these cases, this document presents protocol extensions for
   discussion by the PCE working group and potential inclusion in
   [Stateful-PCE]. In addition, this document presents protocol
   extensions for a set of requirements which are specific to the use
   of a stateful PCE in a GMPLS-controlled network.

   The basic requirements are as follows:

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   o Advertisement and negotiation of the stateful PCE capability. This
     generic requirement is covered in Section 7.1.1 of [Stateful-PCE]
     Section 2.2 of this document discusses other potential extensions
     for this functionality.

   o LSP delegation is already covered in Section 5.5 of [Stateful-
     PCE]. Section 2.3 of this document provides extension for its
     application in GMPLS-controlled networks. Moreover, further
     discussion of some generic details that may need additional
     consideration is provided.

   o LSP synchronization (see [Stateful-APP] Section 2.2). This is a
     generic requirement already covered in Section 5.4 of [Stateful-
     PCE]. However, there are further extensions required specifically
     for GMPLS networks and discussed in Section 2.4.o Reference to
   LSPs by identifiers is discussed in Section 7.2 of
     [Stateful-PCE].  This feature can be applied to reduce the data
     carried in PCEP messages. Use cases and additional Error Codes
     are necessary, as described in Section 2.5 and 2.6.

2.2. Stateful PCE Capability Advertisement and Negotiation

   Whether a PCE has stateful capability or not can be negotiated
   during the PCEP session establishment process. It can also be
   advertised through routing protocols as described in [RFC5088]. In
   either case, the following additional aspects should also be

 2.2.1. PCE Capability Negotiation/Advertisement in Multi-layer Networks

   In multi-layer network scenarios, such as an IP-over-optical network,
   if there are dedicated PCEs responsible for each layer, then the
   PCCs should be informed of which PCEs they should synchronize their
   LSP states with, as well as send path computation requests to. The
   Layer-Cap TLV defined in [INTER-LAYER] can be used to indicate which
   layer a PCE is in charge of. This TLV is optional and MAY be carried
   in the OPEN object. It is RECOMMMENDED that a PCC synchronizes its
   LSP states with the same PCEs that it can use for path computation
   in a multi-layer network. In a single layer, this TLV MAY not be
   used. However, if the PCE capability discovery depends on IGP and if
   an IGP instance spans across multiple layers, this TLV is still

   Alternatively, the extension to current OSPF PCED TLV is needed. A
   new domain-type denoting the layer information can be defined:

   domain-type: T.B.D.

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   When it is carried in PCE-DOMAIN sub-TLV, it denotes the layer for
   which a PCE is responsible for path computation as well as LSP state
   synchronization. When carried in the PCE-NEIG-DOMAIN sub-TLV, it
   denotes its adjacent layers for which a PCE can compute paths and
   synchronize the LSP states. The DOMAIN-ID information can be
   represented using the following format, to denote the layer

    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
   | LSP Enc. Type | Switching Type|             Reserved          |

2.3. LSP Delegation in GMPLS Networks

   To enable the PCE to control an LSP, the PCUpd message is defined in
   [Stateful-PCE]. However, technology-specific specification is not
   covered. The following defines the <path> descriptor that should be
   used in GMPLS networks:



         <attribute-list> ::= [<LSPA>]




         <metric-list>::= <METRIC>[<metric-list>]

   The O bit in the <GENERALIZED-BANDWIDTH> object has no meaning for
   LSP state synchronization and MUST be set to 0. Furthermore, this
   object MAY appear twice, one with R set to 1 and the other with R
   set to 0. This is to denote the asymmetric bandwidth property of the
   updated bi-directional LSP.

   As explained in [stateful-APP], LSP state synchronization and/or LSP
   parameter change controlled by a stateful PCE in a multi-domain
   network is complex and requires well-defined operational procedures
   as well as protocol design.

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   [TBD: protocol extensions]

2.4. LSP Synchronization in GMPLS networks

   For LSP state synchronization of stateful PCEs in GMPLS networks,
   the LSP attributes, such as its bandwidth, associated route as well
   as protection information etc, should be updated by PCCs to PCE LSP
   database (LSP-DB). Note the LSP state synchronization described in
   this document denotes both the bulk LSP report at the initialization
   phase as well as the LSP state report afterwards described in

   As per [Stateful-PCE], it does not cover technology-specific
   specification for state synchronization. Therefore, extensions of
   PCEP protocol for stateful PCE usage in GMPLS networks are required.
   For LSP state synchronization, the objects/TLVs that should be used
   for stateful PCE in GMPLS networks are defined in [PCEP-GMPLS] and
   are briefly summarized as below:




   o Use of IF_ID_ERROR_SPEC. [Stateful-PCE] section 7.2.2 only
   considers  RSVP ERROR_SPEC TLVs. GMPLS extends this to also support
   IF_ID_ERROR_SPEC, for example, to report about failed unnumbered

   o Extended Objects to support the inclusion of the label and
   unnumbered links.

   Per [Stateful-PCE], the PCRpt message is defined for LSP state
   synchronization purpose. PCRpt is used by a PCC to report one or
   more of its LSPs to a stateful PCE. However, the <path> descriptor
   is technology-specific and left undefined.

   For LSP state synchronization in GMPLS networks, the encoding of the
   <path> descriptor is defined as follows:



         <attribute-list> ::= [<LSPA>]


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         <metric-list>::= <METRIC>[<metric-list>]

   The objects included in the <path> descriptor can be found in
   [RFC5440], [PCE-GMPLS] and [RFC5521].

   For all the objects presented in this section, the P and I bit MUST
   be set to 0 since they are only used by a PCC to report its LSP

   In GMPLS networks, the <ERO> object may include a list of the label
   sub-object for SDH/SONET, OTN and DWDM networks. It may also include
   a list of unnumbered interface IDs to denote the allocated resource.
   The <RRO>, <IRO> and <XRO> objects MAY include unnumbered interface
   IDs and labels for networks such as OTN and WDM networks.

   If the LSP being reported is a protecting LSP, the <PROTECTION-
   ATTRIBUTE> TLV MUST be included in the <LSPA> object to denote its
   attributes and restrictions. Moreover, if the status of the
   protecting LSP changes from non-operational to operational, this
   should be synchronized to the stateful PCE. For example, in 1:1
   protection, the combination of S=0, P=1 and O=0 denotes the
   protecting path is set up already but not used for carrying traffic.
   Upon the working path failure, the operational status of the
   aforementioned protecting LSP changes to in-use (i.e., O=1). This
   information should be synchronized with a stateul PCE through a
   PCRpt message.

   The O bit in the <GENERALIZED-BANDWIDTH> object has no meaning for
   LSP state synchronization and MUST be set to 0. Furthermore, this
   object MAY appear twice, one with R set to 1 and the other with R
   set to 0. This is to denote the asymmetric bandwidth property of the
   updated bi-directional LSP.

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2.5.  Modification of Existing PCEP Messages and Procedures

   One of the advantages mentioned in [Stateful-APP] is that the
   stateful nature of a PCE simplifies the information conveyed in PCEP
   messages, notably between PCC and PCE, since it is possible to refer
   to PCE managed state for active LSPs. To be more specific, with a
   stateful PCE, it is possible to refer to a LSP with an unique
   identifier in the scope of the PCC-PCEP session and thus use such
   identifier to refer to that LSP.

 2.5.1. Use cases

   Use Case 1: Assuming a stateful PCE's LSP-DB is up-to-date, a PCC
   (e.g. NMS) requesting for a re-optimization of one or several LSPs
   can send the request with ''R'' bit set and only provides the relevant
   LSP unique identifiers.

   Upon receiving the PCReq message, PCE should be able to correlate
   with one or multiple LSPs with their detailed state information and
   carry out optimization accordingly.

   The handling of RP object specified in [RFC5440] is stated as

   ''The absence of an RRO in the PCReq message for a non-zero-bandwidth
   TE LSP (when the R bit of the RP object is set) MUST trigger the
   sending of a PCErr message with Error-Type="Required Object Missing"
   and Error-value="RRO Object missing for re-optimization."

   If a PCE has stateful capabilities, and such capabilities have been
   negotiated and advertised, specific rules given in [RFC5440] may
   need to be relaxed. In particular, the re-optimization case: if the
   re-optimization request refers to a given LSP state, and the RRO
   information is available, the PCE can proceed.

   Use Case 2: in order to set up a LSP which has a constraint that its
   route should not use resources used by one or more existing LSPs, a
   PCC can send a PCReq with the identifiers of these LSPs. A stateful
   PCE should be able to find the corresponding route and resource
   information so as to meet the constraints set by the requesting PCC.
   Hence, the LSP identifier TLV defined in [Stateful-PCE] can be used
   in XRO object for this purpose. Note that if the PCC is a node in
   the network, the constraint LSP ID information will be confined to
   the LSPs initiated by itself.

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 2.5.2. Modification for LSP Re-optimization

   For re-optimization, upon receiving a path computation request and
   the ''R'' bit is set, the stateful PCE SHOULD still perform the re-
   optimization in the following two cases:

   Case 1: the existing bandwidth and route information of the to-be-
   optimized LSP is provided in the path computation request. This
   information should be provided via <BANDWIDTH>, <GENERARLIZED-
   BANDWIDTH>, <ERO> objects.

   Case 2: the existing bandwidth and route information can be found
   locally in its LSP-DB. In this case, the PCRep and PCReq messages
   need to be modified to carry LSP identifiers. The stateful PCE can
   find this information using the per-node LSP ID together with the
   PCC's address.

   If no LSP state information is available to carry out re-
   optimization, the stateful PCE should report the error ''LSP state
   information unavailable for the LSP re-optimization'' (Error Type =
   T.B.D., Error value= T.B.D.).

 2.5.3. Modification for Route Exclusion

   A LSP identifier sub-object is defined and its format as follows:

       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
     |L|    Type (T.B.D.)    |     Length    |      Reserved         |
     |        LSP ID                           |        Flag         |
     |                                                               |
     //                        Optional TLVs                        //

       L bit:
         The L bit SHOULD NOT be set, so that the subobject represents
   a strict hop in the explicit route.

        Subobject Type for a per-node LSP identifier.

        The Length contains the total length of the subobject in bytes,
   including the Type and Length fields.

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     LSP ID:
         This is the identifier given to a LSP and it is unique on a
   node basis. It is defined in [Stateful-PCE].

         This field is defined in [Stateful-PCE]. It is not used in
   this sub-object and should be ignored upon receipt.

     Optional TLVs:
         Additional TLVs can be defined in the future to provide
   further information to identify a LSP. In this document, no TLVs are

   One or multiple of these sub-objects can be present in the XRO
   object. When a stateful PCE receives a path computation request
   carrying this sub-object, it should find relevant information of
   these LSPs and preclude the resource during the path computation
   process. If a stateful PCE cannot recognize one or more of the
   received LSP identifiers, it should reply PCErr saying ''the LSP
   state information for route exclusion purpose cannot be found''
   (Error-type = T.B.D., Error-value= T.B.D.). Optionally, it may
   provide with the unrecognized identifier information to the
   requesting PCC.

2.6. Additional Error Type and Error Values Defined

   Error Type Meaning

   21(TBD)    LSP state information missing

               Error-value 1: LSP state information unavailable for the
               LSP re-optimization

3. Error-value 2: the LSP state information for route exclusion purpose
   cannot be found IANA Considerations

   IANA is requested to allocate new Types for the TLV/Object defined
   in this document.


4. Manageability Considerations

   The description and functionality specifications presented related
   to stateful PCEs should also comply with the manageability
   specifications covered in Section 8 of [RFC4655]. Furthermore, a
   further list of manageability issues presented in [Stateful-PCE]
   should also be considered.

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   Additional considerations are presented in the next sections.

4.1. Requirements on Other Protocols and Functional Components

   When the detailed route information is included for LSP state
   synchronization (either at the initial stage or during LSP state
   report process), this require the ingress node of an LSP carry the
   RRO object in order to enable the collection of such information.

5. Security Considerations

   The security issues presented in [RFC5440] and [Stateful-PCE] apply
   to this document.

6. Acknowledgement

   We would like to thank Adrian Farrel and Cyril Margaria for the
   useful comments and discussions.

7. References

7.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to indicate
             requirements levels", RFC 2119, March 1997.

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

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

   [RFC5088] Le Roux, JL., Vasseur, J.-P., Ikejiri, Y., Zhang, R.,
             ''OSPF Protocol Extensions for Path Computation Element
             (PCE) Discovery'', RFC 5088, January 2008.

   [INTER-LAYER] Oki, E., Takeda, Tomonori, Le Roux, JL., Farrel, A.,
             Zhang, F., ''Extensions to the Path Computation Element
             communication Protocol(PCEP) for Inter-Layer MPLS and
             GMPLS Traffic Engineering'', draft-ietf-pce-inter-layer-
             ext-08.txt, XX 2013.

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7.2. Informative References

   [Stateful-APP] Zhang, F., Zhang, X., Lee, Y., Casellas, R., Gonzalez
             de Dios, O., "Applicability of Stateful Path Computation
             Element (PCE) ", draft-zhang-pce-stateful-pce-app-03, work
             in progress.

   [Stateful-PCE]Crabbe, E., Medved, J., Varga, R., Minei, I., ''PCEP
             Extensions for Stateful PCE'', draft-ietf-pce-stateful-pce,
             work in progress.

   [PCE-IA-WSON] Lee, Y., Bernstein G., Takeda, T., Tsuritani, T.,
             ''PCEP Extensions for WSON Impairments'', draft-lee-pce-
             wson-impairments, work in progress.

   [PCEP-GMPLS] Margaria, C., Gonzalez de Dios, O., Zhang, F., ''PCEP
             extensions for GMPLS'', draft-ietf-pce-gmpls-pcep-
             extensions, work in progress.

8. Contributors' Address

   Dhruv Dhody
   Huawei Technology
   Leela Palace
   Bangalore, Karnataka 560008


   Yi Lin
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28972914

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Authors' Addresses

   Xian Zhang
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28972913

   Young Lee
   1700 Alma Drive, Suite 100
   Plano, TX  75075

   Phone: +1 972 509 5599 x2240
   Fax:   +1 469 229 5397

   Fatai Zhang
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   P.R. China

   Phone: +86-755-28972912

   Ramon Casellas
   Av. Carl Friedrich Gauss n7
   Castelldefels, Barcelona 08860


   Oscar Gonzalez de Dios
   Telefonica Investigacion y Desarrollo
   Emilio Vargas 6
   Madrid,   28045

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   Phone: +34 913374013

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