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

Expires: June 5, 2014                                  December 4, 2013

   Path Computation Element (PCE) Protocol Extensions for Stateful PCE
                   Usage in GMPLS-controlled 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
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six
   months   and may be updated, replaced, or obsoleted by other
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   as reference   material or to cite them other than as "work in

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on June 5, 2014.

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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 PCE
   communication Protocol (PCEP) extensions needed to support stateful
   PCE functions, without specifying the technology-specific extensions.
   This memo provides extensions required for PCEP so as to enable the
   usage of a stateful PCE capability in GMPLS-controlled 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................... 4
         2.2.1. PCE Capability Advertisement in Multi-layer Networks 4
      2.3. LSP Delegation in GMPLS-controlled Networks............. 5
      2.4. LSP Synchronization in GMPLS-controlled networks.........6
      2.5. Modification of Existing PCEP Messages and Procedures....7
         2.5.1. Use cases ......................................... 8
         2.5.2. Modification for LSP Re-optimization ...............8
         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 Components 10
   5. Security Considerations..................................... 11
   6. Acknowledgement ............................................ 11
   7. References ................................................. 11
      7.1. Normative References................................... 11
      7.2. Informative References................................. 11
   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 interaction between a Path
   Computation Client (PCC) and a PCE, or between two PCEs.  PCEP as
   specified in [RFC 5440] mainly focuses on MPLS networks and the PCEP
   extensions needed for GMPLS-controlled networks are provided in

   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 the deployment of stateful PCEs 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-controlled
   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 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 state synchronization. This is a generic requirement already
      covered in Section 5.4 of [Stateful-PCE].  However, there are
      further extensions required specifically for GMPLS-controlled
      networks and discussed in Section 2.4.  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

   Whether a PCE has stateful capability or not can be advertised
   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 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. (Editor's note: this change is
   currently not included in the current version of the [INTER-LAYER]
   draft. It is expected that it will be included in its next version.)
   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 needed.

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

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   domain-type: T.B.D.

   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-controlled Networks

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



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




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

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

   [TBD: protocol extensions]

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2.4. LSP Synchronization in GMPLS-controlled 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 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 purposes. 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-controlled 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-controlled 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

   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 stateful 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.

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

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   stateful PCE, it is possible to refer to a LSP with a 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.

 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

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   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         |
     |        PLSP-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.

         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.

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     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

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

3.  IANA Considerations

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

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.

   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

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   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,
             work in progress.

7.2. Informative References

   [Stateful-APP] Zhang, X., Minei, I., et al  "Applicability of
             Stateful Path Computation Element (PCE) ", draft-ietf-pce-
             stateful-pce-app, , 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.

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   [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: +86-755-28972645

   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

   Zafar Ali
   Cisco Systems

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