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Versions: 00 01 02 03 04 draft-ietf-pce-hierarchy-extensions

PCE Working Group                                               F. Zhang
Internet-Draft                                                   Q. Zhao
Intended status: Standards Track                     Huawei Technologies
Expires: October 12, 2011                            O. Gonzalez de Dios
                                                          Telefonica I+D
                                                             R. Casellas
                                                                    CTTC
                                                                 D. King
                                                      Old Dog Consulting
                                                          April 12, 2011

                                 Extensions to
              Path Computation Element Communication Protocol (PCEP)
                 for Hierarchical Path Computation Elements (PCE)
                    draft-zhang-pce-hierarchy-extensions-00

Abstract

   The hierachical Path Computation Element (PCE) architecture defined
   in [PCE-HIERARCHY-FWK] allows the optimum sequence of domains to be
   selected, and the optimum end-to-end path to be derived through the
   use of a hierarchical relationship between domains.

   This document defines the Path Computation Element Protocol (PCEP)
   extensions for the purpose of implementing hierarchical PCE
   procedures which are described in [PCE-HIERARCHY-FWK].


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
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   Drafts.

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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on October 12, 2011.

Copyright Notice

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   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction...............................................3
   2. PCEP Extension Requirements................................4
      2.1. New Objective Functions...............................4
      2.2. PCEP Request Qualifiers...............................4
      2.3. Discovery Between Parent and Child PCEs...............4
         2.3.1. Parent PCE Capability Discovery..................5
         2.3.2. PCE Domain and PCE ID Discovery..................5
      2.4. Domain Connectivity Information Collection............5
      2.5. Error Case Handling...................................6
   3. PCEP Extensions............................................6
      3.1. Extensions to OPEN Object.............................7
         3.1.1. OF Codes.........................................7
         3.1.2. OPEN Object Flags................................7
         3.1.3. Domain-ID TLV....................................7
         3.1.4. PCE-ID TLV.......................................8
         3.1.5. Procedures.......................................8
      3.2. Extensions to RP Object...............................9
         3.2.1. RP Object Flags..................................9
         3.2.2. Domain-ID TLV....................................9
         3.2.3. Procedures.......................................9
      3.3. Extensions to NOTIFICATION Object.....................9
         3.3.1. Notification Types...............................10
         3.3.2. Inter-domain Link TLV............................10
         3.3.3. Inter-domain Node TLV............................11
         3.3.4. Domain-ID TLV....................................11
         3.3.5. PCE-ID TLV.......................................11
         3.3.6. Procedures.......................................12
      3.4. Extensions to PCEP-ERROR Object.......................12
         3.4.1. Hierarchy PCE Error-Type.........................12
         3.4.2. Procedures.......................................12
   4. Manageability Considerations...............................13
   5. IANA Considerations........................................13
   6. Security Considerations....................................13
   7. References.................................................13
      7.1. Normative References..................................13
      7.2. Informative References................................13

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1. Introduction

   [PCE-HIERARCHY-FWK] describes a hierarchy PCE architecture which can
   be used for computing the end-to-end paths of inter-domain MPLS
   Traffic Engineering (TE) and GMPLS Label Switched Paths (LSPs). In
   the hierarchy PCE architecture, the parent PCE can compute a domain
   path based on the domain connectivity information and the child PCE
   can compute the intra-domain path based on the domain topology
   information. The end-to-end domain path computing procedures can be
   abstracted as follows:

   o The PCC requests a child PCE to return an inter-domain path.

   o The child PCE forwards the request to the parent PCE.

   o The parent PCE computes one or multiple domain paths from the
     ingress domain to the egress domain.

   o The parent PCE sends the intra-domain path computation requests
     (between the domain border nodes) to the child PCEs which are
     responsible for the domains along the domain path(s).

   o The child PCEs return the intra-domain paths to the parent PCE.

   o The parent PCE constructs the end-to-end inter-domain path based
     on the intra-domain paths and returns the inter-domain path to the
     child PCE.

   o The child PCE forwards the inter-domain path to the PCC.

   This document defines the PCEP extensions for the purpose of
   implementing hierarchy PCE procedures which are described in
   [PCE-HIERARCHY-FWK].

   The document also uses a number of editor notes to describe options
   and alternative solutions. These options and notes will be removed
   before publication.

1.1.  Terminology

   This document uses the terminology defined in [RFC4655] and [RFC5440]
   and [PCE-HIERARCHY-FWK].

1.2.  Requirements Language

   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].


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2. PCEP Extension Requirements

2.1. New Objective Functions

   For inter-domain path computation, there are three new objective
   functions which are defined in section 1.3.1 of [PCE-HIERARCHY-FWK].

   o Minimize the number of boundary nodes used.

   o Limit the number of domains crossed.

   o Disallow domain re-entry.

   During the PCEP session establishment procedure, the PCE  needs to be
   capable of indicating the objective functions (OF) capability in the
   Open message. This information can be, in turn, announced by child
   PCEs and used for selecting the PCE when a PCC want a path that
   satisfies a certain inter-domain objective function.

   When a PCC requests a PCE to compute an inter-domain path, the PCC
   needs also to be capable of indicating the new objective functions
   for inter-domain path.

   For the reasons described above, new OF codes need to be defined for
   the new inter-domain objective functions. Then the PCE can notify its
   new inter-domain objective functions to the PCC by carrying them in
   the OF-list TLV which is carried in the OPEN object.  The PCC can
   specify which objective function code to use, which is carried in the
   OF object when requesting a PCE to compute an inter-domain path.

2.2. PCEP Request Qualifiers

   As described in section 5.8.1 of [PCE-HIERARCHY-FWK], support of the
   H-PCE architecture will introduce two new qualifications as follows:

   o It must be possible for a child PCE to indicate that the request it
     sends to a parent PCE should be satisfied by a domain sequence
     only, that is, not by a full end-to-end path. This allows the child
     PCE to initiate per-domain or backward recursive path computation.

   o A parent PCE needs to be able to ask a child PCE whether a
     particular node address (the destination of an end-to-end path) is
     present in the domain that the child PCE serves.

   To meet the above requirements, the PCEP PCReq message should be
   extended.

2.3. Discovery Between Parent and Child PCEs

   In the H-PCE architecture, the parent PCE does not need to be aware

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   of each child domain topology. Therefore, it is possible that the
   parent PCE does not join the IGP instance of the child PCE domain,
   i.e. there is no IGP discovery mechanism between the parent PCE and
   child PCE.

   Therefore there must be a discovery mechanism for basic PCE
   information between the parent and child PCEs. In this case, PCEP
   needs to provide discovery mechanisms that do not rely on IGP
   announcement/discovery procedures.

   Editors note. A child PCE could forward the topology within PCNtf
   messages or any other mechanisms, without an IGP adjacency. Further
   discussion of the discovery mechanism and scope will be discussed in
   later versions of this document.

2.3.1. Parent PCE Capability Discovery

   As described in [PCE-HIERARCHY-FWK], during the PCEP session
   establishment procedure, the child PCE needs to be capable of
   indicating to the parent PCE whether it requests the parent PCE
   capability or not. The parent PCE needs also to be capable of
   indicating whether its parent capability can be provided to the
   child PCE or not.

2.3.2. PCE Domain and PCE ID Discovery

   A PCE domain is a single domain with an associated PCE. it is
   possible for a PCE to manage multiple domains. The PCE domain may be
   an IGP area or AS.

   The PCE ID is an IPv4 and/or IPv6 address that is used to reach the
   parent/child PCE. It is RECOMMENDED to use an address that is always
   reachable if there is any connectivity to the PCE.

   The PCE ID information and PCE domain identifiers may be provided
   during the PCEP session establishment procedure or the domain
   connectivity information collection procedure.

2.4. Domain Connectivity Information Collection

   As described in [PCE-HIERARCHY-FWK], the parent PCE builds the domain
   topology map either from configuration or from information received
   from each child PCE. A child PCE may report its neighbor domain
   connectivity to its parent PCE. It is reasonable to use PCEP PCNtf
   message to do this procedure. If an IGP adjacency is established
   between parent and children, it could be used for this purpose.

   There are two types of domain border for providing the domain
   connectivity information:


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   o Domain border is a TE link, e.g. the inter-AS TE link which
     connects two ASs.

   o Domain border is a node, e.g. the IGP ABR which connects two IGP
     areas.

   For the inter-AS TE links, the following information needs to be
   notified to the parent PCE:

   o Identifier of advertising child PCE.

   o Identifier of PCE's domain.

   o Identifier of the link.

   o TE properties of the link (metrics, bandwidth)

   o Other properties of the link (technology-specific).

   o Identifier of link end-points.

   o Identifier of adjacent domain.

   For the ABR, the following information needs to be notified to the
   parent PCE:

   o Identifier of the ABR.

   o Identifier of the IGP Area IDs.

2.5. Error Case Handling

   A PCE that is capable of acting as a parent PCE might not be
   configured or willing to act as the parent for a specific child PCE.
   This fact could be determined when the child sends a PCReq that
   requires parental activity (such as querying other child PCEs), and
   could result in a negative response in a PCEP Error (PCErr) message
   and indicate the hierarchy PCE error types.


3. PCEP Extensions

   3.1. Extensions to OPEN Object

   3.1.1. OF Codes

   There are three new OF codes defined here for H-PCE:

   o Name: Minimize the number of Boundary Nodes used (MBN)
     Objective Function Code: (to be assigned by IANA, recommended 9)

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     Description: Find a path P such that passes through the least
     boundary nodes.

   o Name: Minimize the number of Transit Domains (MTD) 10)
     Objective Function Code: (to be assigned by IANA, recommended
     Description: Find a path P such that passes through the least
     transit domains.

   o Name: Disallow Domain Re-entry (DDR)
     Objective Function Code: (to be assigned by IANA, recommended 11)
     Description: Find a path P such that does not entry a domain more
     than once.

3.1.2. OPEN Object Flags

   There are two OPEN object flags defined here for H-PCE:

   o Parent PCE request bit (to be assigned by IANA, recommended bit 0):
     if set it means the child PCE wishes to use the peer PCE as a
     parent PCE.

   o Parent PCE indication bit (to be assigned by IANA, recommended bit
     1): if set it means the PCE can be used as a parent PCE by the peer
     PCE.

   Editors Note. It is possible that a parent PCE will also act as a
   child PCE.

3.1.3. Domain-ID TLV

   The type of Domain-ID TLV is to be assigned by IANA (recommended 7).
   The length is 8 octets. The format of this TLV is defined below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Domain Type         |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Domain ID                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 1: Domain-ID TLV

   Domain Type (8 bits): Indicates the domain type. There are two types
   of domain defined currently:

   o Type=1: the Domain ID field carries an IGP Area ID.

   o Type=2: the Domain ID field carries an AS number.


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   Domain ID (32 bits): Indicates an IGP Area ID or AS number.

   Editors note. It maybe necessary to support 64 bit domain IDs.

3.1.4. PCE-ID TLV

   The type of PCE-ID TLV is to be assigned by IANA (recommended 8).
   The length is 4. The format of this TLV is defined below:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Address Type        |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     PCE IP Address                          //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 2: PCE ID TLV

   Address Type (16 bits): Indicates the address type of PCE IP Address.
   1 means IPv4 address type, 2 means IPv6 address type.

   PCE IP Address: Indicates the reachable address of a PCE.

3.1.5. Procedures

   The OF codes defined in this document can be carried in the OF-list
   TLV of the OPEN object. If the OF-list TLV carries the OF codes, it
   means that the PCE is capable of implementing the corresponding
   objective functions. This information can be used for selecting a
   proper parent PCE when a child PCE wants to get a path that satisfies
   a certain objective function.

   If a child PCE wants to use the peer PCE as a parent, it can set the
   parent PCE request bit in the OPEN object carried in the Open message
   during the PCEP session creation procedure. If the peer PCE does not
   want to provide the parent function to the child PCE, it must send a
   PCErr message to the child PCE and clear the parent PCE indication
   bit in the OPEN object.

   If the parent PCE can provide the parent function to the peer PCE, it
   may set the parent PCE indication bit in the OPEN object carried in
   the Open message during the PCEP session creation procedure.

   The PCE may also report its PCE ID and list of domain ID to the peer
   PCE by specifying them in the PCE-ID TLV and List of Domain-ID TLVs
   in the OPEN object carried in the Open message during the PCEP
   session creation procedure.

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3.2. Extensions to RP Object

3.2.1. RP Object Flags

   o Domain Path Request bit (to be assigned by IANA, recommended bit
     17): if set it means the child PCE wishes to get the domain
     sequence.

   o Destination Domain Query bit (to be assigned by IANA, recommended
     bit 16): if set it means the parent PCE wishes to get the
     destination domain ID.

3.2.2. Domain-ID TLV

   The format of this TLV is defined in section 2.1.3. This TLV can be
   carried in an OPEN object to indicate a (list of) managed domains, or
   carried in a RP object to indicate the destination domain ID when a
   child PCE responds to the parent PCE's destination domain query by a
   PCRep message.

   Editors note. In some cases, the Parent PCE may need to allocate a
   node which is not necessarily the destination node.

3.2.3. Procedures

   If a child PCE only wants to get the domain sequence for a
   multi-domain path computation from a parent PCE, it can set the
   Domain Path Request bit in the RP object carried in a PCReq message.
   The parent PCE which receives the PCReq message tries to compute a
   domain sequence for it. If the domain path computation succeeds the
   parent PCE sends a PCRep message which carries the domain sequence in
   the ERO to the child PCE . The domain sequence is specified as AS or
   AREA ERO sub-objects (type 32 for AS [RFC3209] or type. Otherwise it
   sends a PCReq message which carries the NO-PATH object to the child
   PCE.

   The parent PCE can set the Destination Domain Query bit in a PCReq
   message to query the destination (which is specified in the
   END-POINTS objects) domain ID from a child PCE.  If the child PCE
   knows the destination(s) domain ID, it sends a PCRep message to the
   parent PCE and specifies the domain ID in the Domain-ID TLV which is
   carried in the RP object. Otherwise it sends a PCRep message with a
   NO-PATH object to the parent PCE.

3.3. Extensions to NOTIFICATION Object

   Because there will not be too many PCEP sessions between the child
   PCE(s) and parent PCE, it is recommended that the PCEP sessions
   between them keeping alive all the time . Then the child PCE can
   report all of the domain connectivity information to the parent PCE

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   when the PCEP session is established successfully. It can also notify
   the parent PCE to update or delete the domain connectivity
   information when it detects the changes.

3.3.1. Notification Types

   There is a new notification type defined in this document :

   o Domain Connectivity Information notification-type (to be assigned
     by IANA, recommended 3).

     Notification-value=0: sent from the parent to the child to query
     all of the domain connectivity information maintained by the child
     PCE.

     Notification-value=1: sent from the child to the parent to update
     the domain connectivity information maintained by the child PCE.

     Notification-value=2: sent from the child to the parent to delete
     the domain connectivity information maintained by the child PCE.

3.3.2. Inter-domain Link TLV

   IGP in each neighbor domain can advertise its inter-domain TE link
   capabilities [RFC5316], [RFC5392]. This information can be collected
   by the child PCEs and forwarded to the parent PCE. PCEP Inter-domain
   Link TLV is used for carrying the inter-domain TE link attributes for
   this purpose. Each Inter-domain Link TLV can carry the attributes of
   one inter-domain link at the most.

   The type of Inter-domain Link TLV is to be assigned by IANA
   (recommended 9). The length is variable. The format of this TLV is
   defined below:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Advertise Router ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        sub-TLVS                             //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 3: Inter-domain Link TLV

   Advertise Router ID (32 bits): indicates the router ID which
   advertises the TE LSA or LSP.



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   Sub-TLVs: the OSPF sub-TLVs for a TE link which defined in [RFC5392]
   and other associated OSPF RFCs. It is noted that if the IGP is IS-IS
   for the child domain the sub-TLVs must be converted to the OSPF
   sub-TLVs format when sending this information to the parent PCE
   through PCEP PCNtf message.

   Each inter-domain link is identified by the combination of advertise
   router ID and the link local IP address or link local unnumbered
   identifier. The PCNtf message which is used for notifying the parent
   PCE to update or delete a inter-domain link must contain the
   information identifies a TE link exclusively.

3.3.3. Inter-domain Node TLV

   The Inter-domain Node TLV carries only the two adjacent domain ID and
   the router (IGP ABR) ID.

   The type of Inter-domain Node Information TLV is to be assigned by
   IANA (recommended 10). The length is variable . The format of this
   TLV is defined below:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         ABR ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Area ID1                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Area ID2                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 4 : Inter-domain Node TLV

   ABR ID (32 bits): indicates the domain border router ID.

   Area ID1 & Area ID2 (32 bits): indicates the two neighbor area IDs.

3.3.4. Domain-ID TLV

   The format of this TLV is defined in section 2.1.3. This TLV can be
   carried in a NOTIFICATION object to indicate the domain ID of the
   PCE who sends the PCNtf message.

   Editors note. A PCE may be responsible for several domains, it may be
   beneficial to use a list of TLVs.

3.3.5. PCE-ID TLV

   The format of this TLV is defined in section 2.1.4. This TLV can be


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   carried in a NOTIFICATION object to indicate the PCE ID of the PCE
   who sends the PCNtf message.

3.3.6. Procedures

   When a parent PCE establishes a PCEP session with a child PCE
   successfully, the parent PCE may request the child PCE to report the
   domain connectivity information. This procedure can be done by
   sending a PCNtf message from the parent to the child, setting the
   notification-type to 3 and notification-value to 0 in the
   NOTIFICATION object.

   When a child PCE receives the PCNtf message, it may send all of the
   domain connectivity information to the parent PCE by the PCNtf
   message(s). The notification-type is 3 and notification-value is 1 in
   the NOTIFICATION object. The NOTIFICATION object may carry the
   inter-domain link TLV and inter-domain node TLV to describe the
   inter-domain connectivity information. It is noted that if the child
   PCE dose not support this function, it will ignore the received PCNtf
   message and the parent PCE will not receive the response.

   The child PCE can also update the domain connectivity information by
   re-sending the PCNtf message(s) with the newly information.

   When the child PCE detects a deletion of domain connectivity (e.g.,
   the inter-domain link TLV is aged out), it must notify the parent PCE
   to delete the inter-domain link by sending the PCNtf message. The
   notification-type is 3 and notification-value is 2 in the
   NOTIFICATION object.

3.4. Extensions to PCEP-ERROR Object

3.4.1. Hierarchy PCE Error-Type

   A new PCEP Error-Type is allocated for hierarchy PCE (to be assigned
   by IANA, recommended 11):

   Error-Type     Meaning
   11             Hierarchy PCE error
                  Error-value=1: parent PCE capability can not be
                  provided

3.4.2. Procedures

   When a specific child PCE sends a PCReq to a peer PCE that requires
   parental activity and the peer PCE does not want to act as the parent
   for it, the peer PCE should send a PCErr message to the child PCE and
   specify the error-type (11) and error-value (1) in the PCEP-ERROR
   object.


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4. Manageability Considerations

   TBD.


5. IANA Considerations

   TBD.


6. Security Considerations

   TBD.


7. References

7.1. Normative References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

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

7.2. Informative References

   [RFC3209]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
               and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
               Tunnels", RFC 3209, December 2001.

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

   [RFC5316]   M. Chen, R. Zhang, X. Duan, " ISIS Extensions in
               Support of Inter-Autonomous System (AS) MPLS and GMPLS
               Traffic Engineering ", RFC 5316, December 2008.

   [RFC5392]   M. Chen, R. Zhang, X. Duan, " OSPF Extensions in
               Support of Inter-Autonomous System (AS) MPLS and GMPLS
               Traffic Engineering ", RFC 5316, January 2009.

   [PCE-HIERARCHY-FWK] D. King, A. Farrel, " The Application of the Path
               Computation Element Architecture to the Determination
               of a Sequence of Domains in MPLS and GMPLS ",
               draft-king-pce-hierarchy-fwk-05, September 2010.



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Authors' Addresses

   Fatai Zhang
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China
   Phone: +86-755-28972912
   Email: zhangfatai@huawei.com

   Quintin Zhao
   Huawei Technology
   125 Nagog Technology Park
   Acton, MA  01719
   US
   Email: qzhao@huawei.com

   Oscar Gonzalez de Dios
   Telefonica I+D
   Emilio Vargas 6, Madrid
   Spain
   Email: ogondio@tid.es

   Ramon Casellas
   CTTC - Centre Tecnologic de Telecomunicacions de Catalunya
   Av. Carl Friedrich Gauss n7
   Castelldefels, Barcelona  08860
   Spain
   Email: ramon.casellas@cttc.es

   Daniel King
   Old Dog Consulting
   Email: daniel@olddog.co.uk


















Zhang, et al.                                                 [Page 14]

Internet-Draft                                             April 2011


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