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    Network Working Group                                         E. Oki
    Internet Draft                                                   NTT
    Category: Standards Track                                J-L Le Roux
    Expires: April 2008                                   France Telecom
                                                                A. Farrel
                                                       Old Dog Consulting
                                                            October 2007
 
     Extensions to the Path Computation Element communication Protocol
         (PCEP) for Inter-Layer MPLS and GMPLS Traffic Engineering
 
                    draft-oki-pce-inter-layer-ext-00.txt
 
    Status of this Memo
 
    By submitting this Internet-Draft, each author represents that any
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    Abstract
 
    The Path Computation Element (PCE) provides path computation
    functions in support of traffic engineering in Multi-Protocol Label
    Switching (MPLS) and Generalized MPLS (GMPLS) networks.
 
    MPLS and GMPLS networks may be constructed from layered service
    networks. It is advantageous for overall network efficiency to
    provide end-to-end traffic engineering across multiple network
    layers through a process called inter-layer traffic engineering.
    PCE is a candidate solution for such requirements.
 
 
 
 
 
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     PCEP Extensions for Inter-Layer TE                   October 2007
    The PCE communication Protocol (PCEP) is designed as a
    communication protocol between Path Computation Clients (PCCs) and
    PCEs. This document presents PCEP extensions for inter-layer
    traffic engineering.
 
    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].
 
    Table of Contents
 
    1. Introduction.................................................2
    2. Overview of PCE-Based Inter-Layer Path Computation...........3
    3. Protocol Extensions..........................................4
    3.1.  INTER-LAYER Object........................................4
    3.2.  SWITCH-LAYER Object.......................................5
    3.2.1.  REQ-ADAP-CAP Object......................................7
    4. Procedure....................................................7
    4.1.  Path Computation Request..................................7
    4.2.  Path Computation Reply....................................8
    5. Updated Format of PCEP Messages..............................8
    6. Manageability considerations.................................9
    7. IANA considerations.........................................10
    8. Security Considerations.....................................10
    9. Acknowledgments.............................................10
    10.  References.................................................10
    10.1. Normative Reference......................................10
    10.2. Informative Reference....................................11
    11.  Authors' Addresses.........................................11
    12.  Intellectual Property Statement............................11
 
 
 
 1. Introduction
 
    The Path Computation Element (PCE) defined in [RFC4655] is an
    entity that is capable of computing a network path or route based
    on a network graph, and applying computational constraints. A Path
    Computation Client (PCC) may make requests to a PCE for paths to be
    computed.
 
    A network may comprise multiple layers. These layers may represent
    separations of technologies (e.g., packet switch capable (PSC),
    time division multiplex (TDM), lambda switch capable (LSC))
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
    [RFC3945], separation of data plane switching granularity levels
    (e.g., PSC-1 and  PSC-2, or VC4 and VC12) [MLN-REQ], or a
    distinction between client and server networking roles (e.g.,
    commercial or administrative separation of client and server
    networks). In this multi-layer network, Label Switched Paths (LSPs)
    in lower layers are used to carry upper-layer LSPs. The network
    topology formed by lower-layer LSPs and advertised to the higher
    layer is called a Virtual Network Topology (VNT) [MLN-REQ].
 
    It is important to optimize network resource utilization globally,
    i.e., taking into account all layers, rather than optimizing
    resource utilization at each layer independently. This allows
    better network efficiency to be achieved. This is what we call
    inter-layer traffic engineering. This includes mechanisms allowing
    the computation of end-to-end paths across layers (known as inter-
    layer path computation), and mechanisms for control and management
    of the VNT by setting up and releasing LSPs in the lower layers
    [MLN-REQ].
 
    PCE can provide a suitable mechanism for resolving inter-layer path
    computation issues. The framework for applying the PCE-based path
    computation architecture to inter-layer traffic engineering is
    described in [PCE-INTER-LAYER-FRWK].
 
    The PCE communication protocol (PCEP) is designed as a
    communication protocol between PCCs and PCEs and is defined in
    [PCEP]. A set of requirements for PCEP extensions to support inter-
    layer traffic engineering is described in [PCE-INTER-LAYER-REQ].
 
    This document presents PCEP extensions for inter-layer traffic
    engineering that satisfy the requirements described in [PCE-INTER-
    LAYER-REQ].
 
 2. Overview of PCE-Based Inter-Layer Path Computation
 
    [RFC4206] defines a way to signal a higher-layer LSP which has an
    explicit route that includes hops traversed by LSPs in lower layers.
    The computation of end-to-end paths across layers is called Inter-
    Layer Path Computation.
 
    A Label Switching Router (LSR) in the higher-layer might not have
    information on the lower-layer topology, particularly in an overlay
    or augmented model [RFC3945], and hence may not be able to compute
    an end-to-end path across layers.
 
    PCE-based inter-layer path computation consists of using one or
    more PCEs to compute an end-to-end path across layers. This could
    be achieved by relying on a single PCE that has topology
    information about multiple layers and can directly compute an end-
    to-end path across layers considering the topology of all of the
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
    layers. Alternatively, the inter-layer path computation could be
    performed using multiple cooperating PCEs where each PCE has
    information about the topology of one or more layers (but not all
    layers) and where the PCEs collaborate to compute an end-to-end
    path.
 
    [PCE-INTER-LAYER-FRWK] describes models for inter-layer path
    computation in more detail.
 
 3. Protocol Extensions
 
    This section describes PCEP extensions for inter-layer path
    computation. Three new objects are defined: the INTER-LAYER object,
    the SWITCH-LAYER object, and the REQ-ADAP-CAP object.
 
 3.1.  INTER-LAYER Object
 
    The INTER-LAYER object is optional and can be used in PCReq and
    PCRep messages.
 
    In a PCReq message, the INTER-LAYER object indicates whether inter-
    layer path computation is allowed, the type of path to be computed,
    and whether nested signaling is allowed. When the INTER-LAYER
    object is absent from a PCReq message, the receiving PCE SHOULD
    process as though inter-layer path computation had been explicitly
    disallowed (I-bit set to zero - see below).
 
    In a PCRep message, the INTER-LAYER object indicates whether inter-
    layer path computation has been performed, the type of path that
    has been computed, and whether nested signaling is used.
 
    When a PCReq message includes more than one request, an INTER-LAYER
    object is used per request. When a PCRep message includes more than
    one path per request, an INTER-LAYER object is used per path.
 
 
 
    INTER-LAYER Object-Class is to be assigned by IANA (recommended
    value=18)
 
    INTER-LAYER Object-Type is to be assigned by IANA (recommended
    value=1)
 
 
 
 
 
 
 
 
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
    The format of the INTER-LAYER object body is 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Reserved                                               |N|I|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
    I flag (1 bit): the I flag is used by a PCC in a PCReq message to
    indicate to a PCE whether an inter-layer path is allowed. When the
    I flag is set (one), the PCE MAY perform inter-layer path
    computation and return an inter-layer path. When the flag is clear
    (zero), the path that is returned MUST NOT be an inter-layer path.
 
    The I flag is used by a PCE in a PCRep message to indicate to a PCC
    whether the path returned is an inter-layer path. When the I flag
    is set (one), the path is an inter-layer path. When it is clear
    (zero), the path is contained within a single layer either because
    inter-layer path computation was not performed or because a mono-
    layer path was found notwithstanding the use of inter-layer path
    computation.
 
    N flag (1 bit): the N flag is used by a PCC in a PCReq message to
    indicate to a PCE whether nested signaling is allowed. When the N
    flag is set (one), nested signaling is allowed. When it is clear
    (zero), nested signaling is not allowed.
 
    The N flag is used by a PCE in a PCRep message to indicate to a PCC
    whether nested signaling is required to support the returned path.
    When the N flag is set (one), nested signaling is required. When it
    is clear (zero), nested signaling is not required.
 
    Note that nested signaling is used to support hierarchical
    [RFC4206] or stitched [LSP-STITCH] LSPs according to the physical
    attributes of the network layers.
 
    If the I flag is clear (zero), the N flag has no meaning and MUST
    be ignored.
 
    Reserved bits of the INTER-LAYER object SHOULD be transmitted as
    zero and SHOULD be ignored on receipt. A PCE that forwards a path
    computation request to other PCEs SHOULD preserve the settings of
    reserved bits in the PCReq messages it sends and in the PCRep
    messages it forwards to PCCs.
 
 3.2.  SWITCH-LAYER Object
 
    The SWITCH-LAYER object is optional on a PCReq message and
    specifies switching layers in which a path MUST, or MUST NOT be
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
    established. A switching layer is expressed as a switching type and
    encoding type. The SWITCH-LAYER object MUST NOT be used on a PCRep
    unless an INTER-LAYER object is also present on the PCReq message.
 
    The SWITCH-LAYER object is optional on a PCRep message, where it is
    used with the NO-PATH object in the case of unsuccessful path
    computation to indicate the set of constraints that could not be
    satisfied.
 
    SWTICH-LAYER Object-Class is to be assigned by IANA (recommended
    value=19)
 
    SWTICH-LAYER Object-Type is to be assigned by IANA (recommended
    value=1)
 
    The format of the SWTICH-LAYER object body is 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | LSP Enc. Type |Switching Type | Reserved                    |I|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               .                               |
    //                              .                              //
    |                               .                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | LSP Enc. Type |Switching Type | Reserved                    |I|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    Each row indicates the switching type and encoding type that MUST,
    or MUST NOT be used for specified layer(s) in the computed path.
 
    LSP Encoding Type (8 bits): see [RFC3471] for a description of
    parameters.
 
    Switching Type (8 bits): see [RFC3471] for a description of
    parameters.
 
    I flag (1 bit): the I flag indicates whether or NOT a layer with
    the specified switching type and encoding type MUST be used by the
    computed path. When the I flag is set (one), the computed path MUST
    traverse a layer with the specified switching type and encoding
    type. When the I flag is clear (zero), the computed path MUST NOT
    enter or traverse any layer with the specified switching type and
    encoding type.
 
    A PCC may want to specify only a Switching Type and not an LSP
    Encoding Type. In this case, the LSP Encoding Type is set to zero.
 
 
 
 
 
 
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   3.2.1.
          REQ-ADAP-CAP Object
 
    The REQ-ADAP-CAP object is optional and is used to specify a
    requested adaptation capability for both ends of the lower layer
    LSP. The REQ-ADAP-CAP object is used in inter-PCE communication,
    where the PCE that is responsible for computing higher layer paths
    acts as a PCC to request a path computation from a PCE that is
    responsible for computing lower layer paths.
 
    The REQ-ADAP-CAP object can be carried within a PCReq message and a
    PCRep message. It is used in a PCRep message in case of
    unsuccessful path computation (in this case, the PCRep message also
    contains a NO-PATH object and the REQ-ADAP-CAP object is used to
    indicate the set of constraints that could not be satisfied).
 
    The REQ-ADAP-CAP object MAY be used in a mono-layer network to
    specify a requested adaptation capability for both ends of the LSP.
    In this case, it MAY be carried without INTER-LAYER Object.
 
    REQ-ADAP-CAP Object-Class is to be assigned by IANA (recommended
    value=20)
 
    REQ-ADAP-CAP Object-Type is to be assigned by IANA (recommended
    value=1)
 
    The format of the REQ-ADAP-CAP object body is 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Switching Cap |   Encoding    | Reserved                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    Switching Capability (8 bits): see [RFC4203] for a description of
    parameters.
 
    Encoding (8 bits): see [RFC3471] for a description of parameters.
 
    A PCC may want to specify a Switching Capability, but not an
    Encoding. In this case, the Encoding MUST be set zero.
 
 4. Procedure
 
 4.1.  Path Computation Request
 
    A PCC requests inter-layer path computation in a PCReq message by
    including the INTER-LAYER object with the I flag set. The INTER-
    LAYER object indicates whether inter-layer path computation is
    allowed and whether nested signaling is allowed.
 
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
    The SWITCH-LAYER object, which MUST NOT be present unless the
    INTER-LAYER object is also present, is optionally used to specify
    the switching types and encoding types that define layers that MUST,
    or MUST NOT, be used in the computed path.
 
    The REQ-ADAP-CAP object is optionally used to specify the interface
    switching capability of both ends of the lower layer LSP. The REQ-
    ADAP-CAP object is used in inter-PCE communication, where the PCE
    that is responsible for computing higher layer paths makes a
    request as a PCC to a PCE that is responsible for computing lower
    layer paths.
 
 4.2.  Path Computation Reply
 
    The requested PCE replies to the requesting PCC for the inter-layer
    path computation result in a PCRep message including the INTER-
    LAYER object.
 
    In the case of unsuccessful path computation, the PCRep message
    also contains a NO-PATH object, and the SWITCH-TYPE object and/or
    the REQ-ADAP-CAP MAY be used to indicate the set of constraints
    that could not be satisfied.
 
 5. Updated Format of PCEP Messages
 
    The format of the PCReq message is updated as follows:
 
    <PCReq Message>::= <Common Header>
                       [<SVEC-list>]
                       <request-list>
 
       where:
          <svec-list>::=<SVEC>
                        [<svec-list>]
 
          <request-list>::=<request>[<request-list>]
 
          <request>::= <RP>
                       <END-POINTS>
                       [<OF>]
                       [<LSPA>]
                       [<BANDWIDTH>]
                       [<metric-list>]
                       [<RRO>]
                       [<IRO>]
                       [<LOAD-BALANCING>]
                       [<INTER-LAYER>]
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
                       [<SWITCH-LAYER>]
                       [<REQ-ADAP-CAP>]
       where:
 
       <metric-list>::=<METRIC>[<metric-list>]
 
 
    The format of the PCRep message is updated as follows:
 
    <PCRep Message> ::= <Common Header>
                        <response-list>
 
       where:
          <response-list>::=<response>[<response-list>]
 
          <response>::=<RP>
                      [<NO-PATH>]
                      [<path-list>]
 
          <path-list>::=<path>[<path-list>]
 
          <path>::= <ERO>
                   [<OF>]
                   [<LSPA>]
                   [<BANDWIDTH>]
                   [<metric-list>]
                   [<IRO>]
                   [<INTER-LAYER>]
                   [<SWITCH-LAYER>]
                   [<REQ-ADAP-CAP>]
 
       where:
          <metric-list>::=<METRIC>[<metric-list>]
 
 
 
 6. Manageability considerations
 
    TBD
 
    Manageability of inter-layer traffic engineering with PCE must
    address the following consideration for section 5.1.
 
    - need for a MIB module for control and monitoring
    - need for built-in diagnostic tools
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
    - configuration implication for the protocol
 
 7. IANA considerations
 
    TBD
 
 
 8. Security Considerations
 
    TBD
 
    Inter-layer traffic engineering with PCE may raise new security
    issues when PCE-PCE communication is done between different layer
    networks for inter-layer path computation. Security issues may also
    exist when a single PCE is granted full visibility of TE
    information that applies to multiple layers.
 
    It is expected that solutions for inter-layer protocol extensions
    will address these issues in detail using security techniques such
    as authentication.
 
 9. Acknowledgments
 
 
 10.     References
 
 10.1. Normative Reference
 
    [RFC2119] S. Bradner, "Key words for use in RFCs to indicate
    requirements levels", RFC 2119, March 1997.
 
    [RFC3471] L. Burger, "Generalized Multi-Protocol Label Switching
    (GMPLS)E RFC 3471, January 2003.
 
    [RFC3945] E. Mannie, "Generalized Multi-Protocol Label Switching
    Architecture", RFC 3945, October 2004.
 
    [RFC4203] K. Kompella and Y. Rekhter, "OSPF Extensions in Support
    of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203,
    October 2005.
 
    [RFC4206] K. Kompella, and Y. Rekhter, "Label Switched Paths (LSP)
    Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS)
    Traffic Engineering (TE)", RFC 4206, October 2005.
 
    [PCEP] JP. Vasseur et al, "Path Computation Element (PCE)
    communication Protocol (PCEP) - Version 1 -" draft-ietf-pce-pcep
    (work in progress).
 
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
    [PCE-INTER-LAYER-REQ] E. Oki et al., "PCC-PCE Communication
    Requirements for Inter-Layer Traffic Engineering", draft-ietf-pce-
    inter-layer-req (work in progress).
 
    [PCE-INTER-LAYER-FRWK] E. Oki et al., "Framework for PCE-Based
    Inter-Layer MPLS and GMPLS Traffic Engineering", draft-oki-pce-
    inter-layer-frwk (work in progress)
 
 10.2. Informative Reference
 
    [RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation
    Element (PCE)-Based Architecture", RFC 4655, September 2006.
 
    [MLN-REQ] K. Shiomoto et al., "Requirements for GMPLS-based multi-
    region and multi-layer networks (MRN/MLN)", draft-ietf-ccamp-gmpls-
    mln-reqs (work in progress).
 
    [LSP-STITCH] A. Ayyangar et al., "Label Switched Path Stitching
    with Generalized Multiprotocol Label Switching Traffic Engineering
    (GMPLS TE) ", draft-ietf-ccamp-lsp-stitching (work in progress).
 
 11.     Authors' Addresses
 
    Eiji Oki
    NTT
    3-9-11 Midori-cho,
    Musashino-shi, Tokyo 180-8585, Japan
    Email: oki.eiji@lab.ntt.co.jp
 
    Jean-Louis Le Roux
    France Telecom R&D,
    Av Pierre Marzin,
    22300 Lannion, France
    Email: jeanlouis.leroux@orange-ftgroup.com
 
    Adrian Farrel
    Old Dog Consulting
    Email: adrian@olddog.co.uk
 
 12.     Intellectual Property Statement
 
    The IETF takes no position regarding the validity or scope of any
    Intellectual Property Rights or other rights that might be claimed
    to pertain to the implementation or use of the technology described
    in this document or the extent to which any license under such
    rights might or might not be available; nor does it represent that
    it has made any independent effort to identify any such rights.
    Information on the procedures with respect to rights in RFC
    documents can be found in BCP 78 and BCP 79.
 
 
 
 
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      PCEP Extensions for Inter-Layer TE                   October 2007
    Copies of IPR disclosures made to the IETF Secretariat and any
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    attempt made to obtain a general license or permission for the use
    of such proprietary rights by implementers or users of this
    specification can be obtained from the IETF on-line IPR repository
    at http://www.ietf.org/ipr.
 
    The IETF invites any interested party to bring to its attention any
    copyrights, patents or patent applications, or other proprietary
    rights that may cover technology that may be required to implement
    this standard.  Please address the information to the IETF at ietf-
    ipr@ietf.org.
 
    Disclaimer of Validity
 
    This document and the information contained herein are provided on
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    FOR A PARTICULAR PURPOSE.
 
    Copyright Statement
 
    Copyright (C) The IETF Trust (2007).
 
 
    This document is subject to the rights, licenses and restrictions
    contained in BCP 78, and except as set forth therein, the authors
    retain all their rights.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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