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Versions: (draft-ietf-pce-disco-proto-igp) 00 01 02 03 04 05 06 07 08 RFC 5089

Network Working Group                              J.L. Le Roux (Editor)
Internet Draft                                            France Telecom
Category: Standard Track
Expires: March 2007                                J.P. Vasseur (Editor)
                                                       Cisco System Inc.

                                                          Yuichi Ikejiri
                                                      NTT Communications

                                                           Raymond Zhang
                                                              BT Infonet

                                                          September 2006


  IS-IS protocol extensions for Path Computation Element (PCE) Discovery

                  draft-ietf-pce-disco-proto-isis-00.txt


Status of this Memo

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Abstract

   There are various circumstances in which it is highly desirable for a
   Path Computation Client (PCC) to be able to dynamically and
   automatically discover a set of Path Computation Element(s) (PCE),
   along with some of information that can be used for PCE selection.
   When the PCE is an LSR participating to the IGP, or even a server
   participating passively to the IGP, a simple and efficient way for

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   PCE discovery consists of relying on IGP flooding. For that purpose
   this document defines ISIS extensions for the advertisement of PCE
   Discovery information within an ISIS area or within the entire ISIS
   routing domain.


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.

Table of Contents

   1.      Note........................................................3
   2.      Terminology.................................................3
   3.      Introduction................................................4
   4.      Overview....................................................5
   4.1.    PCE Information.............................................5
   4.1.1.  PCE Discovery Information...................................5
   4.1.2.  PCE Status Information......................................6
   4.2.    Flooding scope..............................................6
   5.      ISIS extensions.............................................6
   5.1.    IS-IS PCED TLV format.......................................6
   5.1.1.  PCE-ADDRESS sub-TLV.........................................7
   5.1.2.  The PATH-SCOPE sub-TLV......................................7
   5.1.3.  PCE-DOMAINS sub-TLV.........................................9
   5.1.3.1.  Area ID DOMAIN sub-TLV...................................10
   5.1.3.2.  AS Number DOMAIN sub-TLV.................................10
   5.1.4.  PCE-DEST-DOMAINS sub-TLV...................................10
   5.1.5.  GENERAL-CAP sub-TLV........................................11
   5.1.6.  The PATH-COMP-CAP sub-TLV..................................12
   5.1.6.1.  Objective Functions sub-TLV..............................13
   5.1.6.2.  Opaque Objective Function sub-TLV........................13
   5.1.6.3.  Switch Caps sub-TLV......................................14
   5.2.    The ISIS PCES TLV..........................................14
   5.2.1.  The CONGESTION sub-TLV.....................................15
   6.      Elements of Procedure......................................16
   6.1.1.  PCES TLV specific procedure................................16
   7.      Backward compatibility.....................................17
   8.      IANA considerations........................................17
   8.1.    ISIS TLVs..................................................17
   8.2.    Capability bits............................................18
   9.      Security Considerations....................................19
   10.     References.................................................19
   10.1.   Normative references.......................................19
   10.2.   Informative references.....................................19
   11.     Authors' Addresses:........................................20
   12.     Intellectual Property Statement............................20




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1. Note

   This document specifies sub-TLVs to be carried within the ISIS Router
   Capability TLV ([ISIS-CAP]). Because this document does not introduce
   any new ISIS element of procedure it will be discussed within the PCE
   Working Group with a review of the ISIS Working Group.

2. Terminology

   Terminology used in this document

      ABR: IGP Area Border Router (L1L2 router).

      AS: Autonomous System.

      ASBR: AS Border Router.

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

      Intra-area TE LSP: A TE LSP whose path does not cross IGP area
      boundaries.

      Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries.


      Inter-area TE LSP: A TE LSP whose path transits through
      two or more IGP areas.

      Inter-AS MPLS TE LSP: A TE LSP whose path transits
      through two or more ASes or sub-ASes (BGP confederations).

      LSR: Label Switch Router.

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

      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.

      PCECP: Path Computation Element Communication Protocol.

      TE LSP: Traffic Engineered Label Switched Path.







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3. Introduction

   [RFC4655] describes the motivations and architecture for a PCE-based
   path computation model for MPLS and GMPLS TE LSPs. The model allows
   the separation of PCE from PCC (also referred to as non co-located
   PCE) and allows cooperation between PCEs. This relies on a
   communication protocol between PCC and PCE, and between PCEs. The
   requirements for such communication protocol can be found in [PCECP-
   REQ] and the communication protocol is defined in [PCEP].

   The PCE architecture requires, of course, that a PCC be aware of the
   location of one or more PCEs in its domain, and also potentially of
   some PCEs in other domains, e.g. in case of inter-domain TE LSP
   computation.

   A network may comprise a large number of PCEs with potentially
   distinct capabilities. In such context it would be highly desirable
   to have a mechanism for automatic and dynamic PCE discovery, which
   would allow PCCs to automatically discover a set of PCEs, along with
   additional information required for PCE selection, and to dynamically
   detect new PCEs or any modification of PCE information.
   Detailed requirements for such a PCE discovery mechanism are
   described in [PCE-DISC-REQ].

   Moreover, it may also be useful to discover when a PCE experiences
   some processing congestion state and exits such state, in order for
   the PCCs to take some appropriate actions (e.g. redirect to another
   PCE). Note that the PCE selection algorithm is out of the scope of
   this document.

   When PCCs are LSRs participating to the IGP (OSPF, ISIS), and PCEs
   are LSRs or a servers also participating to the IGP, an efficient
   mechanism for PCE discovery within thisan IGP routing domain consists
   of relying on IGP advertisements.

   This document defines ISIS extensions allowing a PCE participating to
   the ISIS routing to advertise its location along with some
   information useful for PCE selection, so as to satisfy dynamic PCE
   discovery requirements set forth in [PCE-DISC-REQ]. This document
   also defines extensions allowing a PCE participating to the ISIS
   routing to advertise its potential processing congestion state.

   Generic capability mechanisms for ISIS have been defined in [ISIS-
   CAP] the purpose of which is to allow a router to advertise its
   capability within an ISIS area or an entire ISIS routing domain. Such
   ISIS extensions fully satisfy the aforementioned dynamic PCE
   discovery requirements.

   This document defines two new sub-TLVs (named the PCE Discovery
   (PCED) TLV and the PCE Status (PCES) TLV) for ISIS, to be carried
   within the ISIS Capability TLV ([ISIS-CAP]). The PCE information


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   advertised is detailed in section 4. Protocol extensions and
   procedures are defined in section 5 and 6.

   This document does not define any new ISIS element of procedure but
   how the procedures defined in [ISIS-CAP] should be used.

   The routing extensions defined in this document allow for PCE
   discovery within an ISIS Routing domain. Solutions for PCE discovery
   across AS boundaries are beyond the scope of this document, and for
   further study.

   Similar extensions to OSPF for PCE discovery can be found in [OSPF-
   PCE-DISCO].

4. Overview

4.1. PCE Information

   PCE information advertised within ISIS includes PCE Discovery
   Information and PCE Status information.

4.1.1. PCE Discovery Information

   The PCE Discovery information is comprised of:

   - The PCE location: This an IPv4 and/or IPv6 address that must be
     used to reach the PCE. It is RECOMMENDED to use addresses always
     reachable;

   - The PCE inter-domain functions: this refers to the PCE path
     computation scope (i.e. inter-area, inter-AS, inter-layer…);

   - The PCE domain(s): This is the set of one or more domain(s) where
     the PCE has visibility and can compute paths;

   - The PCE Destination domain(s): This is the set of one or more
      destination domain(s) towards which a PCE can compute paths;

   - A set of general PCECP capabilities (e.g. support for request
     prioritization) and path computation specific capabilities
     (e.g. supported constraints, supported objective functions).

   It may also contain optional elements to describe more complex
   capabilities.

   PCE Discovery information is by nature a static information that does
   not change with PCE activity. Changes in PCE Discovery information
   may occur as a result of PCE configuration updates, PCE
   deployment/activation, PCE deactivation/suppression or PCE failure.
   Hence, this information is not expected to change frequently.



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4.1.2. PCE Status Information

   The PCE Status is optional information that can be used to report a
   PCE processing congested state along with an estimated congestion
   duration. This is a dynamic information, which may change with PCE
   activity.

   Procedures for a PCE to move from a processing congested state to a
   non congested state are beyond the scope of this document, but the
   rate at which a PCE Status change is advertised MUST not impact by
   any mean the IGP scalability. Particular attention should be given on
   procedures to avoid state oscillations.

4.2. Flooding scope

   The flooding scope for PCE Discovery Information can be limited to
   one or more ISIS areas the PCE belongs to or can be extended across
   the entire ISIS routing domain.
   Note that some PCEs may belong to multiple areas, in which case the
   flooding scope may comprise these areas. This could be the case of an
   ABR for instance advertising its PCE information within the backbone
   area and/or a subset of its attached IGP area(s).

5. ISIS extensions

5.1. IS-IS PCED TLV format

   The IS-IS PCED TLV is made of various non ordered sub-TLVs.

   The format of the IS-IS PCED TLV and its sub-TLVs is the same as the
   TLV format used by the Traffic Engineering Extensions to IS-IS [ISIS-
   TE]. That is, the TLV is composed of 1 octet for the type, 1 octet
   specifying the TLV length and a value field.

   The IS-IS PCED TLV has the following format:

      TYPE: To be assigned by IANA
      LENGTH: Variable
      VALUE: set of sub-TLVs

   Sub-TLVs types are under IANA control.

   Currently five sub-TLVs are defined (suggested type values to be
   assigned by IANA):
            Sub-TLV type  Length               Name
                1      variable     PCE-ADDRESS sub-TLV
                2         3         PATH-SCOPE sub-TLV
                3      variable     PCE-DOMAINS sub-TLV
                4      variable     PCE-DEST-DOMAINS sub-TLV
                5      variable     GENERAL-CAP sub-TLV
                6      variable     PATH-COMP-CAP sub-TLV


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   The sub-TLVs PCE-ADDRESS and PATH-SCOPE MUST always be present within
   the PCED TLV.

   The sub-TLVs PCE-DOMAINS and PCE-DEST-DOMAINS are optional. They MAY
   be present in some specific inter-domain cases.

   The sub-TLVs GENERAL-CAP and PATH-COMP-CAP are optional and MAY be
   present in the PCED TLV to facilitate the PCE selection process.

   Any non recognized sub-TLV MUST be silently ignored.

   Additional sub-TLVs could be added in the future to advertise
   additional PCE information.

   The PCED TLV is carried within an ISIS CAPABILITY TLV defined in
   [ISIS-CAP], whose S bit is determined by the desired flooding scope.


5.1.1. PCE-ADDRESS sub-TLV

   The PCE-ADDRESS sub-TLV specifies the IP address that MUST be
   used to reach the PCE. It is RECOMMENDED to make use of an address
   that is always reachable, provided the PCE is alive.

   The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the
   PCED TLV. It MAY appear twice, when the PCE has both an IPv4 and
   IPv6 address. It MUST not appear more than twice.


   The PCE-ADDRESS sub-TLV has the following format:

      TYPE: To be assigned by IANA (Suggested value =1)
      LENGTH: 5 for IPv4 address and 17 for IPv6 address
      VALUE: This comprises one octet indicating the address-type and 4
             or 16 octets encoding the IPv4 or IPv6 address to be used
             to reach the PCE

   Address-type:
                  1   IPv4
                  2   IPv6


5.1.2. The PATH-SCOPE sub-TLV

   The PATH-SCOPE sub-TLV indicates the PCE path computation scope which
   refers to the PCE ability to compute or take part into the
   computation of intra-area, inter-area, inter-AS or inter-layer_TE
   LSP(s).




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   The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the
   PCED TLV. There MUST be exactly one PATH-SCOPE sub-TLV within each
   PCED TLV.

   The PATH-SCOPE sub-TLV contains a set of bit flags indicating the
   supported path scopes (intra-area, inter-area, inter-AS, inter-layer)
   and four fields indicating PCE preferences.

   The PATH-SCOPE sub-TLV has the following format:

   TYPE: To be assigned by IANA (Suggested value =2)
   LENGTH: 3
   VALUE: This comprises a one-byte flag of bits where each bit
          represents a supported path scope, followed by a 2-bytes
          preferences field indicating PCE preferences.

   Here is the structure of the bits flag:

      +-+-+-+-+-+-+-+-+
      |0|1|2|3|4|5|Res|
      +-+-+-+-+-+-+-+-+


   Bit      Path Scope

   0      L bit: Can compute intra-area path
   1      R bit: Can act as PCE for inter-area TE LSPs
                 computation
   2      Rd bit: Can act as a default PCE for inter-area TE LSPs
                  computation
   3      S bit: Can act as PCE for inter-AS TE LSPs computation
   4      Sd bit: Can act as a default PCE for inter-AS TE LSPs
                  computation
   5      Y bit: Can compute or take part into the computation of
                 paths across layers
   6-7   Reserved for future usage.


   Here is the structure of the preferences field

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |PrefL|PrefR|PrefS|PrefY| Res   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Pref-L field: PCE's preference for intra-area TE LSPs computation.

Pref-R field: PCE’s preference for inter-area TE LSPs computation.

Pref-S field: PCE’s preference for inter-AS TE LSPs computation.

Pref-Y field: PCE's preference for inter-layer TE LSPs computation.

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Res: Reserved for future usage.

   The bits L, R, S and Y bits are set when the PCE can act as a PCE for
   intra-area, inter-area, inter-AS and inter-layer TE LSPs computation
   respectively. These bits are non mutually exclusive.

   When set the Rd bit indicates that the PCE can act as a default PCE
   for inter-area TE LSPs computation (the PCE can compute path for any
   destination area). Similarly, when set the Sd bit indicates that the
   PCE can act as a default PCE for inter-AS TE LSPs computation (the
   PCE can compute path for any destination AS).

   When the Rd bit is set, the PCE-DEST-DOMAIN TLV (see 5.1.4) does not
   contain any Area ID DOMAIN sub-TLV.

   Similarly, when the Sd bit is set, the PCE-DEST-DOMAIN TLV does not
   contain any AS DOMAIN sub-TLV.

   The PrefL, PrefR, PrefS and PrefY fields are 3-bit long and allow the
   PCE to specify a preference for each computation scope, where 7
   reflects the highest preference. Such preference can be used for
   weighted load balancing of requests. An operator may decide to
   configure a preference to each PCE so as to balance the path
   computation load among them, with respect to their respective CPU
   capacity. The algorithms used by a PCC to balance its path
   computation requests according to such PCE’s preference are out of
   the scope of this document. Same or distinct preferences may be used
   for different scopes. For instance an operator that wants a PCE
   capable of both inter-area and inter-AS computation to be used
   preferably for inter-AS computation may configure a PrefS higher than
   the PrefR.

   When the L bit, R bit, S or Y bit are cleared the PrefL, PrefR,
   PrefS, PrefY fields MUST respectively be set to 0.

5.1.3. PCE-DOMAINS sub-TLV

   The PCE-DOMAINS sub-TLV specifies the set of domains (areas or AS)
   where the PCE has topology visibility and can compute paths. It
   contains a set of one or more sub-TLVs where each sub-TLV identifies
   a domain.

   The PCE-DOMAINS sub-TLV MUST be present when PCE domains cannot be
   inferred by other IGP information, for instance when the PCE is
   inter-domain capable (i.e. when the R bit or S bit is set) and the
   flooding scope is the entire routing domain.






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   The PCE-DOMAINS sub-TLV has the following format:

   TYPE: To be assigned by IANA (Suggested value =2)
   LENGTH: Variable
   VALUE: This comprises a set of one or more DOMAIN sub-TLVs where
          each DOMAIN sub-TLV identifies a domain where the PCE has
          topology visibility and can compute paths

   DOMAIN Sub-TLVs types are under IANA control.

   Currently two DOMAIN sub-TLVs are defined (suggested type values to
   be assigned by IANA):
            Sub-TLV type  Length               Name
                1      variable     Area ID sub-TLV
                2      variable     AS number sub-TLV

   At least one DOMAIN sub-TLV MUST be present in the PCE-DOMAINS sub-
   TLV.

5.1.3.1. Area ID DOMAIN sub-TLV

   This sub-TLV carries an ISIS area ID. It has the following format

   TYPE: To be assigned by IANA (Suggested value =1)
   LENGTH: Variable
   VALUE: This comprises a variable length ISIS area ID. This is the
          combination of an Initial Domain Part (IDP) and High Order
          part of the Domain Specific part (HO-DSP)

5.1.3.2. AS Number DOMAIN sub-TLV

   The AS Number sub-TLV carries an AS number. It has the following
   format:

   TYPE: To be assigned by IANA (Suggested value =2)
   LENGTH: 4
   VALUE: AS number identifying an AS. When coded on two
          bytes (which is the current defined format as the
          time of writing this document), the AS Number field
          MUST have its left two bytes set to 0.


5.1.4. PCE-DEST-DOMAINS sub-TLV

   The PCE-DEST-DOMAINS sub-TLV specifies the set of destination domains
   (areas, AS) toward which a PCE can compute path. It means that the
   PCE can compute or take part in the computation of inter-domain LSPs
   whose destinations are located within one of these domains. It
   contains a set of one or more DOMAIN sub-TLVs where each DOMAIN sub-
   TLV identifies a domain.


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   The PCE-DEST-DOMAINS sub-TLV has the following format:

   TYPE: To be assigned by IANA (Suggested value =3)
   LENGTH: Variable
   VALUE: This comprises a set of one or more Area or/and AS DOMAIN sub-
          TLVs where each sub-TLV identifies a destination domain toward
          which a PCE can compute path.


   The PCE-DEST-DOMAINS sub-TLV MUST be present if the R bit is set and
   the Rd bit is cleared, and/or, if the S bit is set and the Sd bit is
   cleared.

   The PCE-DEST-DOMAINS sub-TLV MUST include at least one DOMAIN sub-
   TLV. It MUST include at least one area ID sub-TLV, if the R bit of
   the PATH-SCOPE TLV is set and the Rd bit of the PATH-SCOPE TLV is
   cleared. Similarly, it MUST include at least one AS number sub-TLV if
   the S bit of the PATH-SCOPE TLV is set and the Sd bit of the PATH-
   SCOPE TLV is cleared.


5.1.5. GENERAL-CAP sub-TLV

   The GENERAL-CAP sub-TLV is an optional TLV used to indicate PCECP
   related capabilities. It carries a 32-bit flag, where each bit
   corresponds to a general PCE capability. It MAY also include optional
   sub-TLVs to encode more complex capabilities.

   The GENERAL-CAP sub-TLV has the following format:

      TYPE: To be assigned by IANA (Suggested value =4)
      LENGTH: Variable
      VALUE: This comprises a 32-bit General Capabilities flag where
             each bit corresponds to a general PCE capability, and
             optional sub-TLVs that may be defined to specify more
             complex capabilities. Currently no sub-TLVs are defined.


   The following bits in the General Capabilities 32-bit flag are to be
   assigned by IANA:

    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

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |P|M|             Reserved                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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     Bit       Capabilities

      0      P bit: Support for Request prioritization.
      1      M bit: Support for multiple requests within the same
                    request message.

     2-31    Reserved for future assignments by IANA.

5.1.6. The PATH-COMP-CAP sub-TLV

   The PATH-COMP-CAP sub-TLV is an optional TLV used to indicate path
   computation specific capabilities of a PCE.
   It comprises a 32-bit flag, where each bit corresponds to a path
   computation capability. It MAY also include optional sub-TLVs to
   encode more complex capabilities.

   The PATH-COMP-CAP sub-TLV has the following format:

      TYPE: To be assigned by IANA (suggested value = 5)
      LENGTH: Variable
      VALUE: This comprises one 32 bit Path Computation Capabilities
             Flag, where each bit corresponds to a path computation
             capability, and optional sub-TLVs that may be defined to
             specify more complex capabilities. Three optional sub-TLVs
             are currently defined.
   The following bits in the Path Computation Capabilities 32-bit Flag
   are to be assigned by IANA:

    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

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |G|B|D|L|S|0|P|          Reserved                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Bit       Capabilities

      0      G bit: Capability to handle GMPLS link contraints
      1      B bit: Capability to compute bidirectional paths
      2      D bit: Capability to compute link/node/SRLG diverse paths
      3      L bit: Capability to compute load-balanced paths
      4      S bit: Capability to compute a set of paths in a
                    synchronized Manner
      5      O bit: Support for multiple objective functions
      6      P bit: Capability to handle path constraints (e.g. max hop
                    count, metric bound)

     7-31    Reserved for future assignments by IANA.

The G, B, D, L, S, O and P bits are not exclusive.


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   Three optional sub-TLVs are currently defined for the PATH-COMP-CAP
   TLV:
   - The Objective Functions sub-TLV (type to be defined, suggested
      value =1) that carries a list of supported objective functions,
      where each objective function is identified by a 16 bit integer.
   - The Opaque Objective Function sub-TLV (type to be defined,
      suggested value =2) that allows the user to encode a specific
      objective function in any appropriate language.
   - The Switch Caps sub-TLV (type to be defined, suggested value =3)
      that carries a list of supported switching capabilities. This
      means that the PCE can compute paths for the listed switching
      capabilities.

5.1.6.1. Objective Functions sub-TLV

   The format of the Objective Functions sub-TLV is as follows:
         TYPE:     To be defined by IANA (suggested value =1)
         LENGTH:   Variable (N*2)
         VALUE:    This comprises a set of one or more 16 bit function
                   ids, where each function id identifies a supported
                   objective functions.

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             function 1        |   function 2                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                                                             //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             function N        |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Objectives functions and their identification will be defined in a
   separate document.

   The Objective Functions sub-TLV is optional. It MAY be present within
   the PATH-COMP-CAP TLV. When present it MUST be present only once in
   the PATH-COMP-CAP TLV.

5.1.6.2. Opaque Objective Function sub-TLV


The format of the Opaque Objective Function sub-TLV is as follows:

         TYPE:     To be defined by IANA (suggested value =2)
         LENGTH:   Variable
         VALUE:    This encodes a specific objective function in any
                   appropriate language.

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Opaque objective function                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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The Opaque Objective function sub-TLV is optional. The PATH-COMP-CAP TLV
MAY comprise 0, one or more Opaque Objective Functions.


5.1.6.3. Switch Caps sub-TLV

The format of the Switch Caps sub-TLV is as follows:

         TYPE     To be defined by IANA (suggested value =3)
         LENGTH   Variable = N, where N is the number of supported
                  switching capabilities
         VALUE    This comprises a set of one or more 8-bit switching
                  types, where each switching types identifies a
                  supported switching capability.

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   SC type     |   SC type     |   SC type     |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                                                             //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Switching type values are defined in [RFC4205].

The Switch Caps sub-TLV is optional. It MAY be present in the PATH-COMP-
CAP TLV.  When present it MUST be present only once in the PATH-COMP-CAP
TLV.

5.2. The ISIS PCES TLV

   The ISIS PCE Status TLV (PCES TLV) carries information related to PCE
   processing congestion state.
   The PCES TLV is carried within an ISIS Capability TLV which is
   defined in [ISIS-CAP].

   The ISIS PCES TLV has the following format:

      TYPE: To be assigned by IANA
      LENGTH: Variable
      VALUE: set of sub-TLVs

   Sub-TLVs types are under IANA control.

   Currently two sub-TLVs are defined (suggested type values to be
   assigned by IANA):
            Sub-TLV type  Length               Name
                1      variable     PCE-ADDRESS sub-TLV
                2         3         CONGESTION sub-TLV

   The PCE-ADDRESS and CONGESTION sub-TLVs MUST be present once

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   in a PCES TLV. The PCE-ADDRESS sub-TLV is defined in section 6.1.1.
   It carries one of the PCE IP addresses and is used to identify the
   PCE the processing congestion state information is applied to. This
   is required as the PCES and PCED TLVs may be carried in separate
   ISIS Capability TLVs.

   Any non recognized sub-TLV MUST be silently ignored.

   Additional sub-TLVs could be added in the future to advertise
   additional congestion information.

5.2.1. The CONGESTION sub-TLV

   The CONGESTION sub-TLV is used to indicate whether a PCE experiences
   a processing congestion state or not along with optionally the PCE
   expected congestion duration.
   The CONGESTION sub-TLV is mandatory. It MUST be carried once within
   the PCES TLV.

   The format of the CONGESTION sub-TLV is as follows:

   TYPE: To be assigned by IANA (Suggested value =2)
   LENGTH: 3
   VALUE: This comprises a one-byte flag of bits indicating the
          congestion status, followed by a 2-bytes field indicating the
          congestion duration.


   Here is the TLV structure

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|       Reserved|      Congestion Duration      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Value
           -C bit: When set this indicates that the PCE experiences
                   congestion and cannot support any new request. When
                   cleared this indicates that the PCE does not
                   experience congestion an can support a new request.

           -Congestion Duration: 2-bytes, the estimated PCE congestion
                                 duration in seconds.

   When C is set and the Congestion Duration field is equal to 0, this
   means that the Congestion Duration is unknown.
   When C is cleared the Congestion Duration MUST be set to 0.






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6. Elements of Procedure

   The PCED and PCES TLV are carried within an ISIS Capability TLV which
   is defined in [ISIS-CAP].

   As PCES information is likely to change more frequently than the PCED
   information, it is RECOMMENDED to carry PCES and PCED TLVs in
   separate ISIS Capability TLVs, so as not to carry all PCED
   information each time the PCE status changes.

   An ISIS router MUST originate a new ISIS LSP whenever the content
   of any of the PCED TLV or PCES TLV changes or whenever required by
   the regular ISIS procedure (LSP refresh).

   When the scope of the PCED or PCES TLV is area local it MUST be
   carried within an ISIS CAPABILITY TLV having the S bit cleared.
   When the scope of the PCED or PCES TLV is the entire IGP domain, the
   PCED TLV MUST be carried within an ISIS CAPABILITY TLV having the S
   bit set.
   Note that when only the L bit of the PATH-SCOPE sub-TLV is set,
   the flooding scope MUST be local.
   Note that the flooding scopes of the PCED and PCES TLVs may be
   distinct, in which case they are carried in distinct ISIS Capability
   TLVs.

   PCED and PCES sub-TLVs are OPTIONAL. When an ISIS LSP does not
   contain any PCED or PCES sub-TLV, this means that the PCE information
   of that node is unknown.

   Note that a change in PCED or PCES information MUST not trigger any
   SPF computation.

   The way PCEs retrieve their own information is out of the scope of
   this document. Some information may be configured (e.g. address,
   preferences, scope) and other information may be automatically
   retrieved (e.g. areas of visibility).


6.1.1. PCES TLV specific procedure


   When a PCE enters into a processing congestion state, the conditions
   of which are implementation dependent, it SHOULD originate a new ISIS
   LSP with a Capability TLV carrying a PCES TLV with the C bit set and
   optionally a non-null expected congestion duration.

   When a PCE leaves the processing congestion state, the conditions of
   which are implementation dependent, there are two cases:
        - If the congestion duration in the previously originated PCES
   TLV was null, it SHOULD originate a PCES TLV with the C bit cleared
   and a null congestion duration;


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        - If the congestion duration in the previously originated PCES
   TLV was non null, it MAY originate a PCES TLV. Note that in some
   particular cases it may be desired to originate a PCES TLV with the C
   bit cleared if the saturation duration was over estimated.

   The congestion duration allows reducing the amount of ISIS flooding,
   as only uncongested-congested state transitions are flooded.

   An implementation SHOULD support an appropriate dampening algorithm
   so as to dampen ISIS flooding in order to not impact the ISIS
   scalability. It is RECOMMENDED to introduce some hysteresis for
   congestion state transition, so as to avoid state oscillations that
   may impact ISIS performances. For instance two thresholds MAY be
   configured: A resource saturation upper-threshold and a resource
   saturation lower-threshold. An LSR enters the congested state when
   the CPU load reaches the upper threshold and leaves the congested
   state when the CPU load goes under the lower threshold.

   Upon receipt of an updated PCES TLV a PCC should take appropriate
   actions. In particular, the PCC SHOULD stop sending requests to a
   congested PCE, and SHOULD gradually start sending again requests to a
   no longer congested PCE.


7. Backward compatibility

   The PCED and PCES TLVs defined in this document do not introduce any
   interoperability issue.
   An ISIS router not supporting the PCED/PCES TLVs SHOULD just silently
   ignore the TLV as specified in [ISIS-CAP].



8. IANA considerations


8.1. ISIS TLVs

   IANA will assign a new codepoint for the PCED TLV defined in this
   document and carried within the ISIS CAPABILITY TLV.
   IANA is requested to manage sub-TLV types for the PCED TLV.
   Five sub-TLVs types are defined for the PCED TLV and should be
   assigned by IANA:
        -PCE-ADDRESS sub-TLV (suggested value = 1)
        -PATH-SCOPE sub-TLV (suggested value = 2)
        -PCE-DOMAINS sub-TLV (suggested value = 3)
        -PCE-DEST-DOMAINS sub-TLV (suggested value = 4)
        -GENERAL-CAP sub-TLV (suggested value = 5)
        -PATH-COMP-CAP sub-TLV (suggested value = 6)

   Two sub-TLVs types are defined for the PCE-DOMAINS and PCE-DEST-
   DOMAINS TLVs and should be assigned by IANA:

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        -Area ID sub-TLV (suggested value = 1)
        -AS number sub-TLV (suggested value = 2)

   Three sub-TLV types are defined for the PATH-COMP-CAP TLV and should
   be assigned by IANA:
        -Objective Functions sub-TLV (suggested value =1)
        -Opaque Objective Function sub-TLV (suggested value =2)
        -Switch Caps sub-TLV (suggested value =3)


   IANA will assign a new codepoint for the ISIS PCES TLV defined in
   this document and carried within the ISIS CAPABILITY TLV.
   IANA is requested to manage sub-TLV types for the PCES TLV. Two sub-
   TLVs types are defined for this TLV and should be assigned by IANA:
        -PCE-ADDRESS sub-TLV (suggested value = 1)
        -CONGESTION sub-TLV (suggested value = 2)

8.2. Capability bits

   IANA is requested to manage the space of the General Capabilities
   32-bit flag and the Path Computation Capabilities 32-bit flag defined
   in this document, numbering them in the usual IETF notation starting
   at zero and continuing through 31.
   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:
      - Bit number
      - Defining RFC
      - Name of bit

   Currently two bits are defined in the General Capabilities flag. Here
   are the suggested values:
      -0: Support for Request prioritization.
      -1: Support for multiple messages within the same request message

   Currently six bits are defined in the Path Computation Capabilities
   flag. Here are the suggested values:

      -0: Capability to handle GMPLS Constraints
      -1: Capability to compute bidirectional paths
      -2: Capability to compute link/node/SRLG diverse paths
      -3: Capability to compute load-balanced paths
      -4: Capability to compute a set of paths in a
          synchronized Manner
      -5: Support for multiple objective function
      -6: Capability to handle path constraints (e.g. hop count, metric
          bound)







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9. Security Considerations

   This document raises no new security issues for IS-IS.

10. References

10.1. Normative references

   [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.

   [BCP79] Bradner, S., "Intellectual Property Rights in IETF
   Technology", RFC 3979, March 2005.

   [IS-IS] "Intermediate System to Intermediate System Intra-Domain
   Routing Exchange Protocol " ISO 10589.

   [IS-IS-IP] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
   dual environments", RFC 1195, December 1990.

   [IS-IS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic
   Engineering", RFC 3784, June 2004.

   [IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising
   router information", draft-ietf-isis-caps, work in progress.

   [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
   Element (PCE)-based Architecture", RFC4655, august 2006.

   [PCE-DISCO-REQ] Le Roux, J.L., et al. "Requirements for PCE
   discovery", draft-ietf-pce-discovery-reqs, work in progress

   [RFC4205] Kompella, Rekhter, " IS-IS Extensions in Support of
   Generalized Multi-Protocol Label Switching (GMPLS)", RFC4205, October
   2005.


10.2. Informative references

   [PCECP-REQ] Ash, J., Le Roux, J.L., " PCE Communication Protocol
   Generic Requirements", draft-ietf-pce-comm-protocol-gen-reqs, work in
   progress.

   [PCEP] Vasseur et al., “Path Computation Element (PCE) communication
   Protocol (PCEP) - Version 1”, draft-ietf-pce-pcep, work in progress.

   [OSPF-PCE-DISCO] Le Roux, Vasseur, et al., "OSPF Extensions for PCE
   Discovery", draft-ietf-pce-disco-proto-ospf, work in progress.


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11. Authors' Addresses:

   Jean-Louis Le Roux (Editor)
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   FRANCE
   Email: jeanlouis.leroux@orange-ft.com

   Jean-Philippe Vasseur (Editor)
   Cisco Systems, Inc.
   1414 Massachusetts avenue
   Boxborough , MA - 01719
   USA
   Email: jpv@cisco.com

   Yuichi Ikejiri
   NTT Communications Corporation
   1-1-6, Uchisaiwai-cho, Chiyoda-ku
   Tokyo 100-8019
   JAPAN
   Email: y.ikejiri@ntt.com

   Raymond Zhang
   BT Infonet
   2160 E. Grand Ave.
   El Segundo, CA 90025
   USA
   Email: raymond_zhang@infonet.com


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.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   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

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   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 an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

   Copyright Statement

   Copyright (C) The Internet Society (2006).  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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