One document matched: draft-vasseur-pce-monitoring-00.txt


Networking Working Group                                     JP. Vasseur
Internet-Draft                                        Cisco Systems, Inc
Intended status: Standards Track                        October 10, 2006
Expires: April 13, 2007


      A set of monitoring tools for Path Computation Element based
                              architecture
                  draft-vasseur-pce-monitoring-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   A Path Computation Element (PCE) based architecture has been
   specified for the computation of constrained shortest Traffic
   Engineering (TE) Label Switched Paths (LSPs) in Multiprotocol Label
   Switching (MPLS) and Generalized MPLS (GMPLS) networks in the context
   of single or multiple across multiple domains (where a domain is
   referred to as a collection of network elements within a common
   sphere of address management or path computational responsibility



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   such as IGP areas and Autonomous Systems).  In such PCE-based
   environment it is thus critical to monitor the state of the path
   computation chain and potentially gather various performance metrics
   with regards to the set of involved PCE(s) that can used for
   performance monitoring and troubleshooting purposes so as to identify
   a potential bottleneck in the path computation chain.  This document
   specifies procedures and extensions to the Path Computation Element
   Protocol (PCEP) in order to gather such information.

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].


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Path Computation Monitoring messages . . . . . . . . . . . . .  4
     3.1.  Path Computation Monitoring Request message (PCMonReq) . .  5
     3.2.  Path Monitoring Reply message (PCMonRep) . . . . . . . . .  6
   4.  Path Computation Monitoring Objects  . . . . . . . . . . . . .  7
     4.1.  MONITORING Object  . . . . . . . . . . . . . . . . . . . .  7
     4.2.  PCE-ID Object  . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  PROC-TIME Object . . . . . . . . . . . . . . . . . . . . .  9
     4.4.  TIMESTAMP Object . . . . . . . . . . . . . . . . . . . . . 11
   5.  Multi-destination monitoring . . . . . . . . . . . . . . . . . 11
   6.  Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   7.  Element of procedure . . . . . . . . . . . . . . . . . . . . . 12
   8.  Manageability Considerations . . . . . . . . . . . . . . . . . 12
   9.  To be considered in a further revision of this document  . . . 12
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     13.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 15










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1.  Terminology

   ABR: routers used to connect two IGP areas (areas in OSPF or levels
   in IS-IS).

   ASBR: routers used to connect together ASs of a different or the same
   Service Provider via one or more Inter-AS links.

   Boundary Node (BN): a boundary node is either an ABR in the context
   of inter- area TE or an ASBR in the context of inter-AS TE.

   Entry BN of domain(n): a BN connecting domain(n-1) to domain(n).

   Exit BN of domain(n): a BN connecting domain(n) to domain(n+1).

   Inter-AS TE LSP: A TE LSP that crosses an AS boundary.

   Inter-area TE LSP: A TE LSP that crosses an IGP area boundary.

   LSR: Label Switching Router.

   LSP: Label Switched Path.

   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.

   PCE(i) is a PCE with the scope of domain(i).

   TED: Traffic Engineering Database.


2.  Introduction

   The Path Computation Element (PCE) based architecture has been
   specified in [RFC4655] for the computation of constrained shortest
   Traffic Engineering (TE) Label Switched Paths (LSPs) in Multiprotocol
   Label Switching (MPLS) and Generalized MPLS (GMPLS) networks in the
   context of single or multiple across multiple domains (where a domain
   is referred to as a collection of network elements within a common
   sphere of address management or path computational responsibility
   such as IGP areas and Autonomous Systems).

   In such PCE-based environment it is thus critical to monitor the
   state of the path computation chain and potentially gather various
   performance metrics with regards to the set of involved PCE(s) that
   can used for performance monitoring and troubleshooting purposes so
   as to identify a potential bottleneck in the path computation chain.



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   This document specifies procedures and extensions to the Path
   Computation Element Protocol (PCEP) ([I-D.ietf-pce-pcep]) in order to
   monitor the path computation chain and gather various performance
   metrics.  As discussed in [RFC4655], a TE LSP may be computed by one
   PCE (referred to as ) or several PCE (referred to as Multi-PCE).  In
   the former case, the PCC may be able to use IGP extensions to check
   the availability of the PCE (see [I-D.ietf-pce-disco-proto-ospf] and
   [I-D.ietf-pce-disco-proto-isis]) or PCEP using Keepalive messages.
   In constrast, when multiple PCEs are involved in the path computation
   chain an example of which being the use of the BRPC procedure defined
   in [I-D.ietf-pce-brpc], the PCC's visibility is limited to the first
   involved PCE.  Thus, it is critical to define mechanisms in order to
   gether performance metrics along the path computation chain (e.g.
   liveness, path computation time at each PCE, propagation delays
   experienced by the path computation request betwen each PCE involved
   in the path computation chain and so on).


3.  Path Computation Monitoring messages

   As defined in [I-D.ietf-pce-pcep], a PCEP message consists of a
   common header followed by a variable length body made of a set of
   objects that can either be mandatory or optional.  Furthermore, an
   object is said to be mandatory in a PCEP message when the object MUST
   be included for the message to be considered as valid.  Thus a PCEP
   message with a missing mandatory object MUST be considered as a
   malformed message and such condition MUST trigger an Error message.
   Conversely, if an object is optional, the object may or may not be
   present.  The use of the P flag is defined in [I-D.ietf-pce-pcep].
   As a reminder, the P flag is located in the common header of each
   PCEP object that can be set by a PCEP peer to enforce a PCE to take
   into account the related information during the path computation.
   Because the P flag exclusively relates to a path computation request,
   it MUST be cleared in the two PCEP messages (PCEMonReq and PCMonRep
   message) defined in this document.

   For each PCEP message type a set of rules is defined that specify the
   set of objects that the message can carry.  We use the Backus-Naur
   Form (BNF) to specify such rules.  Square brackets refer to optional
   sub-sequences.  An implementation MUST form the PCEP messages using
   the object ordering specified in this document.

   In this document we define two new PCEP messages referred to as the
   Path Computation Monitoring request (PCMonReq) and Path Computation
   Monitoring Reply (PCMonRep) message.  The aim of the PCMonReq message
   sent by a PCC to a PCE is to gather performance metrics on a set of
   PCEs involved in a path computation chain.  The PCMonRep message sent
   by a PCE to a PCC is used to provide such data.



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3.1.  Path Computation Monitoring Request message (PCMonReq)

   The Message-Type field of the PCEP common header for the PCMonReq
   message is set to 8 (To be confirmed by IANA).

   There is one mandatory object that MUST be included within a PCMonReq
   message: the Monitoring object (see section Section 4.1).  If the
   Monitoring object is missing, the receiving PCE MUST send an error
   message to the sender.  Other objects are optional.

   The format of a PCReq message is as follows:
   <PCMonReq Message>::= <Common Header>
                         <MONITORING>
                         [<lsp-request>]
                         [<pce-list>]
   where:

   <lsp-request>::= <RP>
                    <END-POINTS>
                    [<LSPA>]
                    [<BANDWIDTH>]
                    [<METRIC>]
                    [<RRO>]
                    [<IRO>]
                    [<LOAD-BALANCING>]

   <pce-list>::=<pce>[<pce-list>]

   <pce>::= [<PCE-ID>]


   The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, ERO, IRO and LOAD-
   BALANCING objects are defined in [I-D.ietf-pce-pcep].

   A PCMonReq message is sent to gather various performance metrics
   along a path computation chain.  Such metrics may relate to a
   specific path computation chain encoded in the form of a series of
   PCE-ID objects defined in Section 4.2.  Alternatively, it may be
   desired to collect such performance metrics along the path
   computation chain involved to compute a TE LSP.  In that case, the TE
   LSP attributes are characterized by the set of objects present in a
   PCEP Path Computation request (PCReq) message (see
   [I-D.ietf-pce-pcep]).  Several metrics may be requested that are
   specified by a set of objects defined in section Section 4.  Note
   that this set of objects is by all means not limitative and may be
   extended in further revision of this document.  The most simplest
   form of metric is PCE liveness.




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   For the sake of illustraion, consider the two following examples:

   Example 1: PCC1 requests to check the path computation chain should a
   path computation be requested for a specific TE LSP named T1.  A
   PCMonReq message is sent that contains a MONITORING object specifying
   a path computation check, along with the appropriate set of objects
   (e.g.  RP, END-POINTS, ...) that would be included in a PCReq message
   for T1.

   Example 2: PCC1 request to gather the processing time along the path
   computation chain selected for the computation of T1.  In addition to
   the objects listed in example 1, the PCMonReq message also contain
   the PROC-TIME object defined in section Section 4.1.

   Example 3: PCC2 request to gather performance metrics along the
   specific path computation chain <pce1, pce2, pce3, pce7>.  A PCMonreq
   message is sent to PCE1 that contains a set of PCE-ID objects that
   identify PCE1, PCE2, PCE3 and PCE7 respectively.

3.2.  Path Monitoring Reply message (PCMonRep)

   The Message-Type field of the PCEP common header for the PCMonRep
   message is set to 9 (To be confirmed by IANA).

   There is one mandatory objects that MUST be included within a
   PCMonRep message: the Monitoring object (see sectionSection 4.1).  If
   the Monitoring object is missing, the receiving PCE MUST send an
   error message to the requesting PCC.  Other objects are optional.

   The format of a PCReq message is as follows:
   <PCMonRep Message>::= <Common Header>
                         <MONITORING>
                         [<RP>]
                         [<metric-pce-list>]

   where:

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

   <metric-pce>::=[<PCE-ID>]
                  [<PROC-TIME>]
                  [<TIME-STAMP>]

   The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, ERO, IRO and LOAD-
   BALANCING objects are defined in [I-D.ietf-pce-pcep].






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4.  Path Computation Monitoring Objects

   Each new PCEP object defined in the document is compliant to the PCEP
   object format defined in [I-D.ietf-pce-pcep], with the P flag and the
   I flag cleared since these flags are exclusively related to path
   computation request.

4.1.  MONITORING Object

   The MONITORING object MUST be carried within each PCMonReq and
   PCMonRep messages.  The MONITORING object is used to specify the set
   of requested performance metrics.

   The MONITORING Object-Class is to be assigned by IANA (recommended
   value=16)

   The MONITORING Object-Type is to be assigned by IANA (recommended
   value=1)

   The format of the MONITORING 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    |              Flags                |I|P|R|C|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     monitoring-id-number                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Optional TLV(s)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Flags: 18 bits - The following flags are currently defined:

   C (Check) - 1 bit: when set, this indicates that the performance
   metric of interest is the PCE's availability.

   R (Record) - 1 bit: when set, this indicates that the PCE's
   indentifier MUST be included in the corresponding PCMonRep message in
   the form of a PCE-ID object.

   P (Processing Time) - 1 bit: the P bit of the MONITORING object
   carried in a PCMonReq message is set to indicate that the processing
   times is a metric of interest, in which case a PROC-TIME object MUST
   be inserted in the corresponding PCMonRep message.  The P bit MUST
   always be set in a PCMonRep message if also set in the corresponding
   PCMonReq message.



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   I (Incomplete) - 1 bit: the I bit MUST be set by a PCE that supports
   the PCMonReq message, which does not trigger any policy violation but
   that cannot provide the set of required performance metrics for
   unspecified reasons.  Once set, the I bit MUST NOT be changed by a
   receiving PCE.

   Monitoring-id-number (32 bits).  The monitoring-id-number value
   combined with the source IP address of the PCC and the PCE address
   uniquely identify the monitoring request context.  The monitoring-id-
   number MUST be incremented each time a new monitoring is sent to a
   PCE.  The value 0x0000000 is considered as invalid.  If no reply to a
   monitoring request is received from the PCE, and the PCC wishes to
   resend its path computation monitoring request, the same monitoring-
   id-number MUST be used.  Conversely, different monitoring-id-number
   MUST be used for different requests sent to a PCE.  The same
   monitoring-id-number may be used for path computation monitoring
   requests sent to different PCEs.  The path computation monitoring
   reply is unambiguously identified by the IP source address of the
   replying PCE.

   No optional TLVs are currently defined.

4.2.  PCE-ID Object

   The PCE-ID Object is used in a PCMonReq message to record the IP
   address of the PCE for which performance metrics are collected and in
   a PCMonRep message to record the IP address of the PCE reporting
   performance metrics.

   The PCE-ID Object-Class is to be assigned by IANA (recommended
   value=17)

   The PCE-ID Object-Type is to be assigned by IANA (recommended
   value=1)

   The format of the PCE-ID Object is as follows:















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   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        |         Lenght                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      PCE IP Address                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Address-type: 1 IPv4 2 IPv6

   Length 4 (IPv4) or 16 (IPv6)

   PCE IP Address: The PCE IP address.  It is RECOMMENDED to use the
   same IP address as the address used in the PCE-ADDRESS sub-TLV
   defined in [I-D.ietf-pce-disco-proto-ospf] and
   [I-D.ietf-pce-disco-proto-isis]should a dynamic discovery mechanism
   be used for PCE discovery.

4.3.  PROC-TIME Object

   The PROC-TIME object MUST be present within a PCMonRep message if the
   P bit of the MONITORING object carried within the corresponding
   PCMonReq was set.  The PROC-TIME object is used to report various
   processing time related metrics.  The Current-processing-time field
   is used to report the processing time for a particular request the
   characteristics of which are specified in the corresponding PCMonReq
   message.  By constrast, a PCC may request processing time metrics
   that are not related to a particular request, in which case the
   request is qualified as a "general" request.  For example, the PCC
   may want to know the minimum, maximum, average and maximum processing
   times on a particular PCE.  The algorithm(s) used by a PCE to compute
   such metrics are out of the scope of this document but a flag is
   specified that is used to indicate to the requester whether the
   processing time values were estimated or computed.  For example, if
   the processing time for a specific TE LSP computation is requested,
   the PCE may either (1) estimate without performing an actual path
   computation or (2) effectively perform the computation to report the
   processing time.

   Furthermore, the same object can be used to report the processing
   time for a particular request in addition to the general processing
   times computed for all request over a period of time.

   The PROC-TIME Object-Class is to be assigned by IANA (recommended
   value=18)



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   The PROC-TIME Object-Type is to be assigned by IANA (recommended
   value=1)

   The format of the PROC-TIME 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                |           Flags               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Current-processing-time               |E|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Min-processing-time                  |E|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Max-processing-time                  |E|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Average-processing time               |E|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Variance-processing-time              |E|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Flags: 18 bits - No Flags are currently defined:

   E (Estimated) - 1 bit: when set, this indicates that the reported
   metric value is based on estimated processing time as opposed to
   actual computation(s).

   Current-processing-time: This field indicates in milliseconds the
   processing time for the path computation of interest characterized in
   the corresponding PCMonReq message and MUST be set to 0x00000000 if
   the request is a general request (does not relate to a particular
   path computation request).

   Min-processing-time: This field indicates in milliseconds the minimum
   processing time.  The equation/algorithm used to compute this value
   is implementation specific and outside of the scope of this document
   (A PCE may decide to compute the minimum processing time over a
   period of times, for the last N path computation requests, ...).  If
   the G flag of the MONITORING object if cleared then this field MUST
   be set to 0x00000000.

   Max-processing-time: This field indicates in milliseconds the maximum
   processing time.  The equation/algorithm used to compute this value
   is implementation specific and outside of the scope of this document
   (A PCE may decide to compute the minimum processing time over a
   period of times, for the last N path computation requests, ...).  If
   the G flag of the MONITORING object if cleared then this field MUST
   be set to 0x00000000.



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   Average-processing-time: This field indicates in milliseconds the
   average processing time.  The equation/algorithm used to compute this
   value is implementation specific and outside of the scope of this
   document (A PCE may decide to compute the minimum processing time
   over a period of times, for the last N path computation requests,
   ...).  If the G flag of the MONITORING object if cleared then this
   field MUST be set to 0x00000000.

   Variance-processing-time: This field indicates in milliseconds the
   variance of the processing times.  The equation/algorithm used to
   compute this value is implementation specific and outside of the
   scope of this document (A PCE may decide to compute the minimum
   processing time over a period of times, for the last N path
   computation requests, ...).  If the G flag of the MONITORING object
   if cleared then this field MUST be set to 0x00000000.

   More granularity may be introduced in further revision of this
   document to get a monitoring metric for a general request of a
   particular class (e.g. all PCReq of priority X).

4.4.  TIMESTAMP Object

   A TIMESTAMP object will be specified in a further revision of this
   document that could be used to provide indication on the time at
   which a PCMonReq message has been received by a PCE and the time at
   which the PCMonReq message has been relayed to the next-hop PCE or
   the time at which a PCMonRep message has been sent to the requester.


5.  Multi-destination monitoring

   In a further revision of this document, a new object will be
   specified allowing a PCC or a user to gather performance metrics for
   a set of destinations using a single PCMonReq message.  For example,
   using a single PCMonreq message originated by the PCC, performance
   metrics for the set of path computation chains involved in the
   computation of a set of TE LSPs will be gathered.  Such set of
   destinations could be specified in the form of a subnets.


6.  Policy

   The receipt of a PCMonReq message may trigger a policy violation on
   some PCE in which case the PCE MUST send a PCErr message with Error-
   Type=12 and Error-value=1.






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7.  Element of procedure

   Reception of a PCMonReq message: upon receiving a PCMonReq message,

   if the PCE does not support the PCMonReq message, the PCE MUST send a
   PCErr message with Error-type=11 and Error-value=1

   If the PCE supports the PCMonReq message but the request is
   prohibited by policy, the PCE MUST send a PCErr message with Error-
   Type=12 and Error-value=1.

   If the PCE supports the PCMonReq and the request is not prohibited by
   policy, the receiving PCE MUST first determine whether it is the last
   PCE of the path computation chain the process of which is being
   outside of this document.  If the PCE is not the last element of the
   path computation chain, the PCMonReq message is relayed to the next
   hop PCE: such next-hop may either be specified by means of a PCE-ID
   object present in the PCMonReq message or dynamically determined by
   means of a procedure outside of the scope of this document.
   Conversely, if the PCE is the last PCE of the path computation chain,
   the PCE originates a PCMonRep message that contains the requested
   objects according to the set of requested performance metrics listed
   in the MONITORING object carried in the corresponding PCMonReq
   message.

   Reception of a PCMonRep message: upon receiving a PCMonRep message,
   the PCE processes the request, adds the relevant objects to the
   PCMonRep message and forwards the PCMonRep message to the upstream
   requesting PCE or PCC.

   Special case of Multi-destination monitoring: performance monitoring
   request related to more than one destinations may lead to involve a
   set of path computation chains.  In that case, a PCE sends each copy
   of the PCMonReq message to each downstream PCE of each path
   computation chain.


8.  Manageability Considerations

   To be addressed in a further revision of this document.


9.  To be considered in a further revision of this document

   IT might be desirable to modify the format of the PCMonReq and
   PCMonRep messages to support the bundling of multiple performance
   metrics collection for a set of TE LSPs.




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10.  IANA Considerations

   Two new PCEP (specified in [I-D.ietf-pce-pcep]) messages are defined
   in this document:

   Value    Meaning
     8      Path Computation Monitoring Request (PCMonReq)
     9      Path Computation Monitoring Reply (PCMonRep)

   The following new PCEP objects are defined in this document.

   Object-Class      Name

          16         MONITORING
                     Object-Type
                        1

          17         PCE-ID
                     Object-Type
                        1

          18         PROC-TIME
                     Object-Type
                        1

   Two new error types are defined in this document (Error-Type and
   Error-value to be assigned by IANA).

   Error-type          Meaning
       11              Performance Monitoring not supported
                        Error-value
                            1: Monitoring message not supported by one
                               or PCEs along the domain path

       12              Performance Monitoring Policy violation
                            1: Monitoring message supported but rejected
                               due to policy violation



11.  Security Considerations

   To be addressed in a further revision of this document.


12.  Acknowledgements





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13.  References

13.1.  Normative References

   [I-D.ietf-pce-pcep]
              Vasseur, J., "Path Computation Element (PCE) communication
              Protocol (PCEP) - Version 1", draft-ietf-pce-pcep-02 (work
              in progress), June 2006.

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

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

13.2.  Informative References

   [I-D.ietf-pce-brpc]
              Vasseur, J., "A Backward Recursive PCE-based Computation
              (BRPC) procedure to compute  shortest inter-domain Traffic
              Engineering Label Switched Paths", draft-ietf-pce-brpc-00
              (work in progress), August 2006.

   [I-D.ietf-pce-disco-proto-isis]
              Roux, J., "IS-IS protocol extensions for Path Computation
              Element (PCE) Discovery",
              draft-ietf-pce-disco-proto-isis-00 (work in progress),
              September 2006.

   [I-D.ietf-pce-disco-proto-ospf]
              Roux, J., "OSPF protocol extensions for Path Computation
              Element (PCE) Discovery",
              draft-ietf-pce-disco-proto-ospf-00 (work in progress),
              September 2006.


Author's Address

   JP Vasseur
   Cisco Systems, Inc
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Email: jpv@cisco.com






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