IETF Internet Draft PCE Working Group                 Jerry Ash (AT&T)
Proposed Status: Informational                                  Editor
Expires: November 2005                   J.L. Le Roux (France Telecom)

                                                              May 2005


         PCE Communication Protocol Generic Requirements

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Copyright Notice

   Copyright (C) The Internet Society (2005).


   Constraint-based path computation is a fundamental building block for
   traffic engineering systems such as multiprotocol label switching
   (MPLS) and generalized multiprotocol label switching (GMPLS)
   networks.  Path computation in large, multi-domain or multi-layer
   networks is highly complex and may require special computational
   components and cooperation between the different network domains.

   There are multiple components in the Path Computation Element (PCE)-
   based path computation model, including PCE discovery and the PCE
   communication protocol.  The PCE model is described in the "PCE
   Architecture" document and facilitates path computation requests from
   Path Computation Clients (PCCs) to PCEs.  This document specifies
   generic requirements for a communication protocol between PCCs and
   PCEs, and between PCEs where cooperation between PCEs is desirable.
   Subsequent documents will specify application-specific requirements
   for the PCE communication protocol.

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Table of Contents

1. Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . . . 3
3. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Overview of PCE Communication Protocol  . . . . . . . . . . . . . 4
6. PCE Communication Protocol Generic Requirements . . . . . . . . . 5
   6.1 Basic Protocol Requirements . . . . . . . . . . . . . . . . . 5
       6.1.1 Client-Server Communication . . . . . . . . . . . . . . 6
       6.1.2 PCC-PCE and PCE-PCE Communication . . . . . . . . . . . 7
       6.1.3 Reliable Message Exchange . . . . . . . . . . . . . . . 7
       6.1.4 Secure Message Exchange . . . . . . . . . . . . . . . . 8
       6.1.5 Request Prioritization  . . . . . . . . . . . . . . . . 8
       6.1.6 Unsolicited Notifications . . . . . . . . . . . . . . . 8
       6.1.7 Asynchronous Communication  . . . . . . . . . . . . . . 8
       6.1.8 Communication Overhead Minimization . . . . . . . . . . 9
       6.1.9 Extensibility . . . . . . . . . . . . . . . . . . . . . 9
       6.1.10 Scalability  . . . . . . . . . . . . . . . . . . . . . 9
   6.2 Deployment Support Requirements . . . . . . . . . . . . . . . 10
       6.2.1 Support for Various Service Provider Environments and
             Applications  . . . . . . . . . . . . . . . . . . . . . 10
       6.2.2 Confidentiality . . . . . . . . . . . . . . . . . . . . 10
   6.3 Detection & Recovery Requirements . . . . . . . . . . . . . . 10
       6.3.1 Aliveness Detection . . . . . . . . . . . . . . . . . . 10
       6.3.2 PCC/PCE Failure Response  . . . . . . . . . . . . . . . 10
       6.3.3 Protocol Recovery . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Manageability Considerations  . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12
11. Normative References . . . . . . . . . . . . . . . . . . . . . . 12
12. Informational References . . . . . . . . . . . . . . . . . . . . 13
13. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
14. Intellectual Property Considerations . . . . . . . . . . . . . . 14

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1. Contributors

   This document is the result of the PCE Working Group PCE
   communication protocol requirements design team joint effort. The
   following are the design team member authors that contributed to the
   present document:

   Jerry Ash (AT&T)
   Alia Atlas (Avici)
   Arthi Ayyangar (Juniper)
   Nabil Bitar (Verizon)
   Igor Bryskin (Independent Consultant)
   Dean Cheng (Cisco)
   Durga Gangisetti (MCI)
   Kenji Kumaki (KDDI)
   Jean-Louis Le Roux (France Telecom)
   Eiji Oki (NTT)
   Raymond Zhang (BT Infonet)

2. 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].

3. Introduction

   The path computation element (PCE) capability [PCE-ARCH] supports
   requests for path computation issued by a path computation client
   (PCC), which may be co-located or remote from a PCE.  When the PCC is
   remote from the PCE, a request/response communications protocol is
   required to carry the path computation request and return the
   response.  In order for the PCC and PCE to communicate, the PCC must
   discover the location of the PCE, as described in [PCE-DISC-REQ].
   The PCE operates on a network graph in order to compute paths based
   on the path computation request issued by the PCC, which will
   normally include the source, destination, and a set of constraints.
   The PCE response includes the computed paths or the reason for a
   failed computation.

   This document lists a set of generic requirements for the PCE
   communication protocol, where the PCE communications protocol
   solution MUST satisfy these requirements.  Application-specific
   requirements are beyond the scope of this document, and will be
   addressed in separate documents.

4. Terminology

   Domain: any collection of network elements within a common sphere of
   address management or path computational responsibility.  Examples of
   domains include IGP areas, Autonomous Systems (ASs), multiple ASs

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   within a service provider network, or multiple ASs across multiple
   service provider networks.

   GMPLS: generalized multiprotocol label switching

   LSP: MPLS Label Switched Path.

   MPLS: multiprotocol label switching

   PCC: Path Computation Client: any client application requesting a
   Path computation to be performed by the PCE.

   PCE: Path Computation Element: an entity (component, application or
   network node) that is capable of computing a network path or route
   based on a network graph and applying computational constraints (see
   further description in [PCE-ARCH]).

   TED: Traffic Engineering Database, which contains the topology and
   resource information of the network or network segment used by a PCE.

   TE LSP: Traffic Engineering MPLS Label Switched Path.

   See [PCE-ARCH] for further definitions of terms.

5. Overview of PCE Communication Protocol

   In the PCE model, path computation requests are issued by a PCC
   to a PCE that may be co-located or situated at a remote site.  If
   the PCC and PCE are not co-located a request/response communications
   protocol is required to carry the request and return the response. If
   the PCC and PCE are co-located a communications protocol is not
   required, but implementations may choose to utilize a protocol for
   exchanges between the components.

   In order that a PCC and PCE can communicate, the PCC must know the
   location of the PCE. This can be configured or discovered. The PCE
   discovery mechanism is out of scope of this document, but
   requirements are documented in [PCE-DISC-REQ].

   The PCE operates on a network graph built from the TED in order to
   compute paths. The mechanism by which the TED is populated is out of
   scope for the PCE Communications Protocol.

   A path computation request issued by the PCC will include a
   specification of the path(s) needed. The information supplied will
   include at a minimum the source and destination for the path(s), but
   may also include a set of further requirements (known as constraints)
   as described in Section 6.

   The response from the PCE may be positive in which case it will
   include the paths that have been computed. If the computation fails

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   or cannot be performed, a negative response is required with an
   indication of the type of and reason(s) for the failure. A negative
   response may also include further details of the reason(s) for the
   failure, and potentially advice about which constraints might be
   relaxed to be more likely to achieve a positive result.  That is, the
   PCE SHOULD provide sufficient information for the PCC to know whether
   it has to relax constraints or query another PCE.

   A request/response protocol is also required for a PCE to communicate
   path computation requests to another PCE and for the PCE to return
   the path computation response.  As described in [PCE-ARCH], there is
   no reason to assume that two different protocols are needed, and this
   document assumes that a single protocol will satisfy all requirements
   for PCC-PCE and PCE-PCE communications.

   [PCE-ARCH] describes four models of PCE: composite, external,
   multiple PCE path computation and multiple PCE path computation with
   inter-PCE communication.  In all cases except the composite PCE
   model, a communication protocol is required.  The requirements
   defined in this document therefore are applicable to all models
   described in the [PCE-ARCH] except the composite PCE model.

6. PCE Communication Protocol Generic Requirements

   The designers of a PCE communication protocol MUST take the
   requirements set out in this document and discuss them widely within
   the IETF and particularly within the Applications Area to determine
   whether a suitable protocol already exists.  The results of this
   investigation MUST be published on the PCE mailing list.

6.1 Basic Protocol Requirements

6.1.1 Client-Server Communication

   PCC-PCE and PCE-PCE communication is by nature client-server based.
   The communication protocol MUST allow for a PCC or a PCE to send a
   path request message to a PCE, and for a PCE to reply with a path
   response message to the requesting PCC or PCE, once the path has been
   computed.  In addition to this request-response model, there may be
   cases where there is unsolicited communication from the PCE to PCC
   (see Requirement 6.1.6).

   The protocol MUST be capable of returning any explicit path that
   would be acceptable for use for MPLS and GMPLS LSPs once converted to
   an Explicit Route Object for use in RSVP-TE signaling.  Note that the
   resultant path(s) may be made up of a set of strict or loose hops, or
   any combination of strict and loose hops. Moreover, a hop may have
   the form of a non-explicit abstract node.  See RFC 3209 for the
   definition of strict hop, loose hop, and abstract node.

   It MUST be possible to send multiple path computation requests,

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   correlated or not, within the same path request message.  There are
   various motivations for doing so (optimality, path diversity, etc.).

   It MUST be possible to limit by configuration the number of requests
   that can be carried within a single message.  The transport protocol
   MUST allow sending unlimited size messages, but MUST be able to limit
   message size, to avoid a big message from unduly delaying a small
   message.  Maximum message size MAY be negotiated at session
   initialization.  If the number of correlated requests exceeds the
   maximum message size, then separate messages MAY be sent with an
   indication that they are correlated.

   The path request message MUST include, at least, a source and a
   destination, and MAY include a set of one or more path constraints,
   such as the requested bandwidth or resources (hops, affinities, etc.)
   to include/exclude (e.g., a PCC requests the PCE to exclude points of
   failure in the computation of the new path if an LSP setup fails).

   The path request message MUST support the ability to prefer/customize
   various path computation objective functions, policies and
   optimization criteria.  For example, a PCC may be aware of and would
   like to choose from among various objective functions that a PCE may
   offer, and the PCE communication protocol SHOULD allow this to be
   specified per path computation request.  This capability to prefer
   certain objective functions depends on the fact that the PCE
   advertises this to a PCC or that the PCC requests one of a set of
   objective functions defined as a minimal subset that MUST be
   supported by any PCE.

   The requester MUST be allowed to select from the advertised list or
   minimal subset of standard objective functions and functional
   options.  The requester SHOULD also be able to select a
   vendor-specific or experimental objective function or functional
   option.  Furthermore, the requester MUST be allowed to customize the
   objective function/options in use.  That is, individual objective
   functions will often have parameters to be set in the request from
   PCC to PCE.  Specification of objective functions and objective
   function parameters is required in the protocol extensibility
   specified in Section 6.1.9.

   If a PCC selects an objective function that the PCE does not support,
   the PCE response MUST be negative.

   Note that a PCC MAY send a request that is based on the set of TE
   parameters carried by the MPLS/GMPLS LSP setup signaling protocol,
   and as long as those parameters are satisfied, the PCC MAY not care
   about which objective function is used.  Also, the PCE MAY execute
   objective functions not advertised to the PCC, for example, policy
   based routing path computation for load balancing instructed by the
   management plane.

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   A PCC or PCE MUST be able to cancel a pending request.

   The path response message MUST allow returning various elements
   including, at least, the computed path.  It MUST be possible to
   return multiple paths within the same path response message,
   corresponding either to the same request (e.g. load balancing) or to
   distinct requests of the same path request message or distinct path
   request messages.

6.1.2 PCC-PCE and PCE-PCE Communication

   A single protocol MUST be defined for PCC-PCE and PCE-PCE
   communication.  A PCE requesting a path from another PCE can be
   considered as a PCC.

6.1.3 Reliable Message Exchange

   The PCE communication protocol MUST run on top of a reliable
   transport protocol.  In particular, it MUST allow for the detection
   and recovery of lost messages to occur quickly and not impede the
   operation of the communication protocol.  Here the PCE communication
   protocol includes a number of application-specific capabilities, all
   of which run on top of a common, reliable transport protocol layer.

   In some particular cases (e.g. link failure), a large number of PCCs
   may simultaneously send a request to a PCE, leading potentially to a
   saturation of request buffers on PCEs.  The PCE communication
   protocol MUST properly handle such overload situations without a
   significant decrease in performance, such as through throttling of
   such requests.

   The PCE communication-protocol transport MUST provide:

   - acknowledged message delivery with retransmission, as discussed in
     Section 6.1.1
   - in order message delivery.  For the set of requests between a given
     PCC and a PCE, the ordering is already there relying on the
     reliable transport layer.  For requests between a set of PCCs and a
     given PCE, the ordering of responses SHOULD be based on the PCE's
     own handling policy, as well as the priority of the requests.
   - message corruption detection
   - flow control and back-pressure, as specified above with the
     throttling of requests.

   These requirements SHOULD be satisfied by an existing reliable
   transport protocol, and functionality SHOULD only be added where the
   transport protocol does not provide it (e.g., rapid partner failure
   detection).  With regard to the rapid partner failure detection, the
   PCC MUST be informed of any failed PCE (or PCE connection) when it

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6.1.4 Secure Message Exchange

   The PCC-PCE and PCE-PCE communication MUST be secure. In particular,
   it MUST support mechanisms to prevent spoofing (e.g.,
   authentication), snooping (e.g., encryption) and DOS attacks.

6.1.5 Request Prioritization

   The communication protocol MUST support the notion of request
   priority, allowing a PCC to specify the degree of urgency of a
   particular request.  This is used to serve some requests before
   others, and would require global prioritization.  That is, a request
   from one PCC can have a higher priority than a request from another
   PCC to the same PCE.  However, there is no intention or need for a
   PCE to preempt (i.e., discard) a given request from one PCC if it
   receives a higher-priority request from another PCC; the PCE just
   delays the lower-priority request.

   If, for example, the PCE is processing a low priority request that
   will take extended computation time (e.g., for full re-optimization
   of 1000 protected LSPs through a complex algorithm), it is
   RECOMMENDED that the low priority request to set up a new LSP be
   suspended/interrupted until the high priority request can be
   completed.  The PCE must consider, however, in addition to the
   priority of the path computations, the PCE policy based on its system
   resources, configurations, etc.  That is, the handling of priority on
   the PCE is not entirely in the purview of the PCE communication
   protocol design.

   The PCE communication protocol design MUST consider whether request
   if starvation can occur for particular priorities, whether that is
   acceptable, and how that is handled.

6.1.6 Unsolicited Notifications

   The PCE communication protocol SHOULD support unsolicited
   notifications from PCE to PCC or from PCE to PCE.  That is, the
   normal mode is for the PCC to make path computation requests to the
   PCE.  This requirement includes cases of PCEs computing paths without
   being asked by a PCC, and the PCE sending those unsolicited paths to
   PCCs.  This could also include PCE overload notifications.

6.1.7 Asynchronous Communication

   The PCC-PCE protocol MUST allow for asynchronous communication.  A
   client MUST NOT have to wait for a response to make another request.
   Also it MUST be possible to have the order of some responses differ
   from the order of their corresponding requests.  This may occur, for
   instance, when path request messages have distinct priorities (see
   Requirement 6.1.5).

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6.1.8 Communication Overhead Minimization

   The request and response messages SHOULD be designed so that the
   communication overhead is minimized.  Particular attention SHOULD be
   given to the message size.  Other considerations in overhead
   minimization include the following:

   - the number of messages exchanged to arrive at a computation answer
   - the amount of background messages to keep the session up
   - the processing cost at the PCE (or PCC) associated with

6.1.9 Extensibility

   The PCE communication protocol MUST provide a way for introduction of
   new path computation constraints, diversity types, objective
   functions, optimization methods and parameters, etc., without
   requiring modifications in the protocol.  In particular, the PCE
   communication protocol SHOULD allow supporting future applications
   not currently in the scope of the PCE working group, such as, for
   instance, P2MP path computations.

   The communication protocol MUST allow supporting various PCE based
   applications that have been currently identified and MAY be
   identified in the future, such as:

   - intra-area path computation
   - inter-area path computation
   - inter-AS intra provider and inter-AS inter-provider path
   - multi-layer and virtual network topology computation

   Note that application specific requirements are out of the scope of
   this document and will be addressed in separate requirements

6.1.10 Scalability

   The PCE communication protocol MUST scale well with an increase of
   any of the following parameters:

   - number of PCCs
   - number of PCEs
   - number of PCCs communicating with a single PCE
   - number of PCEs communicated to by a single PCC
   - number of PCEs communicated to by another PCE.
   - TED size (number of links/nodes, which may drive up path
     computation time)
   - number of domains
   - number of path requests
   - handling bursts of requests

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   Bursts of requests may arise, for example, after a network outage
   when multiple recomputations are requested as a result. It is
   RECOMMENDED that the protocol handle the congestion in a graceful way
   so that it does not unduly impact the rest of the network, and so
   that it does not gate the ability of the PCE to perform computation.

6.2 Deployment Support Requirements

6.2.1 Support for Various Service Provider Environments and Applications

   The communication protocol MUST operate in various service provider
   network environments, where the IP control plane is deployed, such as

   - MPLS-TE and GMPLS networks
   - centralized and distributed PCE path computation
   - single and multiple PCE path computation

   Definitions of centralized, distributed, single, and multiple PCE
   path computation can be found in [PCE-ARCH].

6.2.2 Confidentiality

   The communication protocol MUST allow minimizing the amount of
   topological information exchanged between a PCC and PCE, and between
   PCEs.  This is of particular importance in inter-PCE communication,
   where the PCEs are located in distinct service-provider domains.
   For example, the protocol design SHOULD enable policies to be
   implemented such that domain-specific topology information is
   excluded on inter-PCE, inter-domain communication.

6.2.3 Policy Support

   The communication protocol MUST allow for policies to accept/reject
   requests, and include the ability for a PCE to reject requests with
   sufficient detail to allow the PCC to determine the reason for
   rejection or failure.  For example, filtering could be required for
   intra-AS PCE path computation such that all requests are rejected
   that come from another AS.  However, specific policy details
   are left to application-specific communication protocol requirements.
   Furthermore, the communication protocol MUST allow for the
   notification of a policy violation.  Actual policies, configuration
   of policies, and applicability of policies are out of scope.

6.3 Detection & Recovery Requirements

6.3.1 Aliveness Detection

   The PCE communication protocol MUST allow a PCC to check the
   liveliness of PCEs it is using for path computation and a PCE to
   check the liveliness of PCCs it is serving.  The PCE communication

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   protocol MUST provide partner failure detection.

   Depending on the design, this requirement MAY be met by the PCE
   communication protocol design or the transport protocol design.

6.3.2 PCC/PCE Failure Response

   Appropriate PCC and PCE procedures MUST be defined to deal with PCE
   and PCC failures.  A PCC MUST be able to clear any pending request to
   a PCE.  That is, the PCC MAY cancel a previously-made path
   computation request to a PCE.

   Similarly, a PCE MUST be able to clear pending requests from a PCC,
   for instance, when it detects the failure of the requesting PCC or
   when its buffer of requests is full.  It is RECOMMENDED that a PCC
   select another PCE upon detection of PCE failure or unreachability of
   a PCE but note that PCE selection procedure are out of the scope of
   this document.

   It is assumed that the underlying reliable communication mechanism
   ensures reciprocal knowledge of PCE and PCC liveness.  Therefore it
   NOT possible for the PCC/PCE to believe that the PCE/PCC is
   unreachable, but not vice versa.

6.3.3 Protocol Recovery

   Information distributed in asynchronous/unsolicited messages SHOULD
   be allowed to persist at the recipient in the event of the failure of
   the sender or of the communications channel. Upon recovery, the
   communications protocol MUST support resynchronization of information
   between the sender and the receiver, and this SHOULD be arranged so
   as to minimize repeat data transfer.

   For example, the communication protocol SHOULD allow a stateful
   PCE to resynchronize and recover states (e.g., LSP status, paths,
   etc.) after a restart.  Recovery would require the PCE communication
   protocol to support recovery of state information in the PCE.  This
   would be of particular importance when local PCE recovery is not
   supported or fails.

7. Security Considerations

   The impact of the use of a PCE-based architecture MUST be considered
   in the light of the impact that it has on the security of the
   existing routing and signaling protocols and techniques in use within
   the network. There is unlikely to be any impact on intra-domain
   security, but an increase in inter-domain information flows and the
   facilitation of inter-domain path establishment may increase the
   vulnerability to security attacks.

   Of particular relevance are the implications for confidentiality

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   inherent in a PCE-based architecture for multi-domain networks. It
   is not necessarily the case that a multi-domain PCE solution will
   compromise security, but solutions MUST examine their impacts in this

   Applicability statements for particular combinations of signaling,
   routing and path computation techniques are expected to contain
   detailed security sections.

   It should be observed that the use of a non-local PCE (that is, not
   co-resident with the PCC) does introduce additional security issues.
   Most notable amongst these are:

   - interception of PCE requests or responses
   - impersonation of PCE
   - falsification of TE information
   - denial of service attacks on PCE or PCE communication mechanisms

   It is expected that PCE solutions will address these issues in detail
   using authentication and security techniques.

8. Manageability Considerations

   Manageability of the PCE communication protocol MUST address the
   following considerations:

   - need for a MIB module for control and monitoring
   - need for built-in diagnostic tools (e.g., partner failure
     detection, OAM, etc.)
   - configuration implications for the protocol

9. IANA Considerations

   This document makes no requests for IANA action.

10. Acknowledgements

   The authors would like to extend their warmest thanks to (in
   alphabetical order) Adrian Farrel, Thomas Morin, and JP Vasseur for
   their review and suggestions.

11. Normative References

   [PCE-ARCH] Farrel, A., Vasseur, JP, Ash, J., "Path Computation
   Element (PCE) Architecture", work in progress.

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

   [RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
   3667, February 2004.

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   [RFC3668] Bradner, S., "Intellectual Property Rights in IETF
   Technology", BCP 79, RFC 3668, February 2004.

12. Informational References

   [PCE-DISC-REQ] Le Roux, JL, et. al., "Requirements for Path
   Computation Element (PCE) Discovery," work in progress.

   [RFC3209] Awduche, D., et. al., "RSVP-TE: Extensions to RSVP for LSP
   Tunnels," RFC 3209, December 2001.

13. Authors' Addresses

   Jerry Ash
   Room MT D5-2A01
   200 Laurel Avenue
   Middletown, NJ 07748, USA
   Phone: +1-(732)-420-4578

   Alia K. Atlas
   Avici Systems, Inc.
   101 Billerica Avenue
   N. Billerica, MA 01862, USA
   Phone: +1 978 964 2070

   Arthi Ayyangar
   Juniper Networks, Inc.
   1194 N.Mathilda Ave
   Sunnyvale, CA 94089 USA

   Nabil Bitar
   40 Sylvan Road
   Waltham, MA 02145

   Igor Bryskin
   Independent Consultant

   Dean Cheng
   Cisco Systems Inc.
   3700 Cisco Way
   San Jose CA 95134 USA
   Phone: +1 408 527 0677

PCE Design Team <draft-ash-pce-comm-protocol-gen-reqs-01.txt> [Page 13]

Internet Draft   PCE Communication Protocol Generic Reqmnts    May 2005

   Durga Gangisetti

   Kenji Kumaki
   KDDI Corporation
   Garden Air Tower
   Iidabashi, Chiyoda-ku,
   Tokyo 102-8460, JAPAN
   Phone: +81-3-6678-3103

   Jean-Louis Le Roux
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex, FRANCE

   Eiji Oki
   Midori-cho 3-9-11
   Musashino-shi, Tokyo 180-8585, JAPAN

   Raymond Zhang
   BT INFONET Services Corporation
   2160 E. Grand Ave.
   El Segundo, CA 90245 USA

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PCE Design Team <draft-ash-pce-comm-protocol-gen-reqs-01.txt> [Page 14]

Internet Draft   PCE Communication Protocol Generic Reqmnts    May 2005

   rights that may cover technology that may be required to implement
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Disclaimer of Validity

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Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
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PCE Design Team <draft-ash-pce-comm-protocol-gen-reqs-01.txt> [Page 15]