[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 RFC 6007

Network Working Group                                        I. Nishioka
Internet Draft                                                       NEC
Intended status: Informational                               Daniel King
Created: February 10, 2010                            Old Dog Consulting
Expires: August 10, 2010

     The use of SVEC (Synchronization VECtor) list for Synchronized
                      dependent path computations

                draft-ietf-pce-pcep-svec-list-04.txt


Abstract

   A Path Computation Element (PCE) may be required to perform
   dependent path computations. Dependent path computations are
   requests that need to be synchronized in order to meet specific
   objectives. An example of a dependent request would be a PCE
   computing a set of services which are required to be diverse
   (disjointed) from each other. When a PCE computes sets of dependent
   path computation requests concurrently, it is required to use the
   Synchronization VECtor (SVEC) list for association among the sets of
   dependent path computation requests. The SVEC object is optional and
   carried within the Path Computation Element Protocol (PCEP)
   PCRequest (PCReq) message.

   This document does not specify the PCEP SVEC object or procedure.
   This informational document clarifies the use of the SVEC list for
   synchronized path computations when computing dependent requests.
   The document also describes a number of usage scenarios for SVEC
   lists within single domain and multi-domain environments.


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

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

   This Internet-Draft will expire on August 10, 2010.

Nishioka & King            Expires August 10, 2010            [Page 1]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document.  Code Components extracted from this
   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008. The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s)
   controlling the copyright in such materials, this document may not
   be modified outside the IETF Standards Process, and derivative works
   of it may not be created outside the IETF Standards Process, except
   to format it for publication as an RFC or to translate it into
   languages other than English.






















Nishioka & King            Expires August 10, 2010            [Page 2]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


Table of Contents

   1. Introduction ..................................................3
 1.1. SVEC Object ...................................................4
 1.2. Application of SVEC Lists .....................................4
   2. Terminology ...................................................6
   3. SVEC association scenarios ....................................6
 3.1. Synchronized computation for diverse path requests ............6
 3.2. Synchronized computation for point-to-multipoint path
      requests ......................................................8
   4. SVEC association ..............................................8
 4.1. SVEC list .....................................................8
 4.2. Associated SVECs ..............................................8
 4.3. Non-associated SVECs ..........................................9
   5. Processing of SVEC list ......................................10
 5.1. Single PCE, single domain environments .......................10
 5.2. Multi-PCE, single domain environments ........................11
 5.3. Multi-PCE, multi-domain environments .........................11
   6. End-to-end diverse path computation ..........................12
 6.1. Disjoint VSPT ................................................12
 6.2. Disjoint VSPT encoding .......................................14
 6.3. Path computation procedure ...................................14
   7. Manageability considerations .................................15
 7.1. Control of Function and Policy ...............................15
 7.2. Information and Data Models, e.g. MIB modules ................15
 7.3. Liveness Detection and Monitoring ............................15
 7.4. Verifying Correct Operation ..................................15
 7.5. Requirements on Other Protocols and Functional Components.....16
 7.6. Impact on Network Operation ..................................16
   8. Security Considerations ......................................16
   9. IANA Considerations ..........................................17
   10. References ..................................................17
 10.1. Normative References ........................................17
 10.2. Informative References ......................................18
   11. Acknowledgements ............................................18


1. Introduction

   [RFC5440] describes the specifications for PCEP (Path Computation
   Element communication Protocol). PCEP specifies the communication
   between a Path Computation Client (PCC) and a Path Computation
   Element (PCE), or between two PCEs based on the PCE architecture
   [RFC4655]. PCEP interactions include path computation requests and
   path computation replies.






Nishioka & King            Expires August 10, 2010            [Page 3]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   The PCE may be required to compute independent and dependent path
   requests. Path computation requests are said to be independent if
   they are not related to each other, and therefore not required to be
   synchronized. Equally a set of dependent path computation requests,
   that are required to be synchronized, cannot be performed
   independently of each other. The Synchronization VECtor (SVEC) with
   a list of the path computation request identifiers carried within
   the request message allows the PCC or PCE to specify a list of
   multiple path computation requests that must be synchronized.
   Section 1.1 (SVEC Object) describes the SVEC object. Section 1.2
   (Application of SVEC Lists) describes the application of SVEC lists
   in certain scenarios.

   This informational document clarifies the handling of dependent and
   synchronized path computation requests, using the SVEC list, based
   on the PCE architecture [RFC4655] and PCEP [RFC5440]. The document
   also describes a number of usage scenarios for SVEC lists within
   single domain and multi-domain environments. This document is not
   intended to specify the procedure when using SVEC lists for
   dependent and synchronized path computation requests.

1.1. SVEC Object

   When a PCC or PCE sends path computation requests to a PCE, a PCEP
   Path Computation Request (PCReq) message may carry multiple requests
   each of which has a unique path computation request identifier. The
   SVEC with a list of the path computation request identifiers carried
   within the request message allows the PCC or PCE to specify a list
   of multiple path computation requests that must be synchronized, and
   also allows the specification of any dependency relationships
   between the paths. The path computation requests listed in the SVEC
   must be handled in a relation to each other (i.e. synchronized).

   [RFC5440] defines two synchronous path computation modes for
   dependent or independent path computation requests specified by the
   dependency flags (i.e. Node, Link or SRLG diverse flags) in the SVEC.
   (See [RFC5440] for more details of dependent, independent and
   synchronous path computation.)

   o A set of independent and synchronized path computation requests,

   o A set of dependent and synchronized path computation requests.

   These computation modes are exclusive each other in a single SVEC.
   If one of the dependency flags in a SVEC is set, it indicates a set
   of synchronous path computation requests has a dependency and does
   not allow any other path computation requests. In order to be
   synchronized with other path computation requests with a dependency,
   it is necessary to associate them.

Nishioka & King            Expires August 10, 2010            [Page 4]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   The aim of the SVEC object carried within a PCReq message is to
   request the synchronization of M path computation requests. Each
   path computation request is uniquely identified by the Request-ID-
   number carried within the respective RP object.  The SVEC object
   also contains a set of flags that specify the synchronization type.
   The SVEC Object is defined in Section 7.13 (SVEC Object) of
   [RFC5440].

1.2. Application of SVEC Lists

   It is important for the PCE, when performing path computations, to
   synchronize any path computation requests with a dependency. For
   example, consider two protected end-to-end services:

   o It would be beneficial for each back-up path to be disjointed so
     they do not share the same links and nodes as the working path.

   o Two diverse path computation requests would be needed to compute
     the working and disjointed protected paths.

   If the diverse path requests are computed sequentially, fulfillment
   of the initial diverse path computation without consideration of the
   second diverse path computation and disjoint constraint may result in
   the PCE providing sub-optimal path disjoint results for the protected
   path, or may fail to meet the end-to-end disjoint requirement
   altogether.

   Additionally, SVEC can be applied to end-to-end diverse path
   computations that traverse multiple domains. [RFC5441] describes two
   approaches, synchronous (i.e. simultaneous) and 2-step approaches,
   for the end-to-end diverse path computation across a chain of
   domains. The path computation procedure is specified for the 2-step
   approaches in [RFC5521], but no guidelines are provided for a
   synchronous approach which is described in this document.

   The following scenarios are specifically described within this
   document:

   o Single domain, single PCE, dependent and synchronized path
     computation request.

   o Single domain, multi-PCE, dependent and synchronized path
     request.

   o Multi-domain, dependent and synchronized path computation request,
     including end-to-end diverse path computation.






Nishioka & King            Expires August 10, 2010            [Page 5]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   The association among multiple SVECs for multiple sets of
   synchronized dependent path computation is also described in this
   document, as well as disjoint Virtual Shortest Path Tree (VSPT)
   encoding rule for end-to-end diverse path computation across domains.
   Path computation algorithms for these path computation scenarios are
   out of the scope of this document.

   The clarifications and use cases in this document are applicable to
   the Global Concurrent Optimization (GCO) path computation mechanism
   specified in [RFC5557].  The GCO application provides the capability
   to optimize a set of services within the network, in order to
   maximize efficient use of network resources. A single or set of
   objective functions (OFs) can be applied to a GCO. To compute a set
   of such traffic-engineered paths for the GCO application, PCEP
   supports the synchronous and dependent path computation requests
   required in [RFC4657].

   The SVEC association and the disjoint VSPT described in this
   document do not require any extension to PCEP messages and object
   formats, when computing a GCO for multiple or end-to-end diverse
   paths. In addition, the use of multiple SVECs is not restricted to
   only SRLG, Node and Link diversity currently defined in the SVEC
   object [RFC5440], but is also available for other dependent path
   computation requests.

   The SVEC association and disjoint VSPT are available to both single
   PCE path computation and multi-PCE path computation.

2. Terminology

   This document uses PCE terminology defined in [RFC4655], [RFC4875],
   and [RFC5440].

   Associated SVECs: A group of multiple SVECs (Synchronization
   VECtors), defined in this document, to indicate a set of
   synchronized or concurrent path computations.

   Disjoint VSPT: A set of VSPTs, defined in this document, to indicate
   a set of virtual diverse path tree.

   GCO (Global Concurrent Optimization): A concurrent path computation
   application, defined in [RFC5557], where a set of TE paths is
   computed concurrently in order to efficiently utilize network
   resources.

   Synchronized: A set of path computation requests is said to be
   synchronized if the PCE associates the requests, and does not
   compute each request independently of each other.

   VSPT: Virtual Shortest Path Tree defined in [RFC5441].

Nishioka & King            Expires August 10, 2010            [Page 6]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


3. SVEC association scenarios

   This section clarifies several path computation scenarios, in which
   SVEC association can be applied. Also, any combination of scenarios
   described in this section could be applicable.

3.1. Synchronized computation for diverse path requests

   A PCE may compute two or more point-to-point diverse paths,
   concurrently, in order to increase the probability of meeting
   primary and secondary path diversity (or disjointness) objective and
   network resource optimization objective.

   Two scenarios can be considered for the SVEC association of point-
   to-point diverse paths.

   o Two or more end-to-end diverse paths

   When concurrent path computation of two or more end-to-end diverse
   paths is requested, SVEC association is needed among diverse path
   requests. Note here that each diverse path request consists of
   primary, secondary, and tertiary and beyond path requests, in which
   all path requests are grouped with one SVEC association.

   Consider two end-to-end services that are to be kept separate by
   using diverse paths. The path computation requests would need to be
   associated so that diversity could be assured. Consider further that
   each of these services requires a backup path that can protect
   against any failure in the primary path. These backup paths must be
   computed using requests that are associated with the primary paths
   giving rise to a set of four associated requests.

   o End-to-end primary path and its segmented secondary paths

   When concurrent path computation for segment recovery paths, as
   shown in figure 1, is requested, SVEC association is needed between
   a primary path and several segmented secondary paths.

               <------------ primary ----------->

                A------B------C---D------E------F

                  \          /     \          /

                    P---Q---R         X---Y---Z

                <--secondary1-->   <--secondary2-->

                 Figure 1: Segment Recovery Paths


Nishioka & King            Expires August 10, 2010            [Page 7]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   In this scenario, we assume that the primary path may be pre-
   computed, which is used for specifying the segment for secondary
   paths. Otherwise, the segment for secondary path requests are
   specified in advance, by using Exclude Route Object (XRO) and/or
   Include Route Object (IRO) constraints in the primary request.

3.2. Synchronized computation for point-to-multipoint path requests

   For point-to-multipoint path requests, SVEC association can be
   applied.

   o Two or more point-to-multipoint paths

   If a point-to-multipoint paths request is represented as a set of
   point-to-point paths [ID.pce-p2mp-ext], two or more point-to-
   multipoint path computation requests can be associated for
   concurrent path computation, in order to optimize network resources.

   o Point-to-multipoint paths and their secondary paths

   When concurrent path computation of a point-to-multipoint path and
   its point-to-point secondary paths [RFC4875], or a point-to-
   multipoint path and its point-to-multipoint secondary paths is
   requested, SVEC association is needed among these requests. In this
   scenario, we use the same assumption as "end-to-end primary path and
   its segmented secondary paths scenario" in section 3.1.


4. SVEC association

   This section describes the associations among SVECs in a SVEC list.

4.1. SVEC list

   PCEP provides the capability to carry one or more SVEC objects in a
   PCReq message, and this set of SVEC objects within the PCReq message
   is termed a SVEC list. Each SVEC object in the SVEC list contains a
   distinct group of path computation requests. When requesting
   association among such distinct groups, associated SVECs described
   in this document are used.

4.2. Associated SVECs

   "Associated SVECs" defines that there are relationships among
   multiple SVECs in SVEC list. Note that there is no automatic
   association in [RFC5440] between the members of one SVEC and the
   members of another SVEC in the same SVEC list. The associated SVEC
   is introduced to associate these SVECs, especially for correlating
   among SVECs with dependency flags.


Nishioka & King            Expires August 10, 2010            [Page 8]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010

   Request identifiers in the SVEC objects are used to indicate the
   association among SVEC objects. If the same request-IDs exist in
   SVEC objects, this indicates these SVEC objects are associated. When
   associating among SVEC objects, at least one request identifier must
   be shared between associated SVECs. The SVEC objects can be
   associated regardless of the dependency flags in each SVEC object,
   but it is recommended to use a single SVEC if the dependency flags
   are not set in all SVEC objects.

   Below is an example of associated SVECs. In this example, the first
   SVEC is associated with the other SVECs, and all of path computation
   requests contained in the associated SVECs (i.e. Request-ID#1,#2,#3,
   #4, #X, #Y) must be synchronized.

       <SVEC-list>

           <SVEC> without dependency flags

            Request-ID #1, Request-ID #3, Request-ID #X

           <SVEC> with one or more dependency flags

            Request-ID #1, Request-ID #2

           <SVEC> with one or more dependency flags

            Request-ID #3, Request-ID #4

           <SVEC> without dependency flag

            Request-ID #X, Request-ID #Y, Request-ID #Z


4.3. Non-associated SVECs

   Non-associated SVECs mean that there are no relationships among
   SVECs. If none of the SVEC objects in the SVEC list on a PCReq
   message contains a common request-ID, there is no association
   between the SVECs and so no association between the requests in one
   SVEC and the requests in another SVEC.

   Below is an example of non-associated SVECs that does not contain
   any common request-IDs.









Nishioka & King            Expires August 10, 2010            [Page 9]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   <SVEC-list>

       <SVEC> with one or more dependency flags

       Request-ID #1, Request-ID #2

       <SVEC> with one or more dependency flags

       Request-ID #3, Request-ID #4

       <SVEC> without dependency flags

       Request-ID #X, Request-ID #Y, Request-ID #Z


5. Processing of SVEC list

5.1. Single PCE, single domain environments

   In this environment, there is a single PCE within the domain.

   When a PCE receives PCReq messages with more than one SVEC objects
   in the SVEC list, PCEP has to first check the request-IDs in all
   SVEC objects in order to identify any associations among them.

   If there are no matching request-IDs in the different SVEC objects,
   these SVEC objects are not associated, and then each set of path
   computation requests in the non-associated SVEC objects has to be
   computed separately.

   If there are matching request-IDs in the different SVEC objects,
   these SVEC objects are associated, and then all path computation
   requests in the associated SVEC objects are treated in a synchronous
   manner for GCO application.

   If the PCE does not have capability to handle the associated SVEC
   objects, it may send a PCErr message with Error-Type="Capability not
   supported".

   In the case that M path computation requests are sent across
   multiple PCReq messages, the PCE may start a SyncTimer as
   recommended in Section 7.13.3 (Handling of the SVEC Object)
   [RFC5440]. In this case, the associated SVECs should also be handled
   as described in [RFC5440]. I.E. after receiving the entire set of M
   path computation requests associated by SVECs, the computation
   should start at one. If the  SyncTimer has expired or the following
   PCReq messages have been malformed; the PCE should cancel the path
   computation request and respond to the PCC with the relevant PCErr
   message.



Nishioka & King            Expires August 10, 2010            [Page 10]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


5.2. Multi-PCE, single domain environments

   There are multiple PCEs in a domain, to which PCCs can communicate
   directly, and PCCs can choose an appropriate PCE for load balanced
   path computation requests. In this environment it is possible
   dependent path computation requests are sent to different PCEs.

   If a PCC sends path computation requests to a PCE and then sends
   another path computation requests, which are dependent on the first
   requests and has been associated by using a SVEC list. There is no
   method for the PCE to correlate the dependent requests sent to
   different PCEs. No SVEC object correlation function between the PCEs
   is specified in [RFC5440]. As indentified, no mechanism exists to
   resolve this problem and the issue is open for future study.
   Therefore, a PCC must not send dependent path computation requests
   associated by SVECs to different PCEs.

5.3. Multi-PCE, multi-domain environments

   In this environment, there are multiple domains in which PCEs are
   located in each domain, and end-to-end dependent paths (i.e. diverse
   path) is computed using multiple PCEs. Note that we assume a chain
   of PCEs are pre-determined and the BRPC procedure [RFC5441] is in
   use.

   The SVECs can be applied to end-to-end diverse path computations
   that traverse multiple domains. [RFC5441] describes two approaches,
   synchronous (i.e. simultaneous) and 2-step approaches, for the end-
   to-end diverse path computation across a chain of domains. In the 2-
   step approaches described in [RFC5521], it is not necessary to use
   the associated SVECs because any of dependency flags in a SVEC
   object are not set. On one hand, the simultaneous approach may
   require the associated SVEC because at least one of dependency flags
   is required in a SVEC object. Thus, a use case of the simultaneous
   approach is described in this environment.

   When a chain of PCEs located in separate domains are used for
   simultaneous path computations, additional path computation
   processing is required. It is described in this document (Section 6).

   If the PCReq message contains multiple associated SVEC objects and
   these SVEC objects contain path computation requests that will be
   sent to the next PCE along the path computation chain, the following
   procedures are applied.







Nishioka & King            Expires August 10, 2010            [Page 11]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   When a chain of PCEs is a unique sequence for all of path
   computation requests in a PCReq message, it is not necessary to re-
   construct associations among SVEC objects. Thus, the PCReq message
   is passed to the tail end PCE. When a PCReq message contains more
   than one SVEC objects with the dependency flag set, the contained
   SVECs may then be associated. PCEs receiving the associated SVECs
   must maintain their association, and consider their relationship in
   path computing after receiving a corresponding PCRep message.

   When a chain of PCEs is different, it is required that intermediate
   PCEs receiving such PCReq messages may re-construct associations
   among SVEC objects, and then send PCReq messages to corresponding
   PCEs located in neighboring domains. If the associated SVECs are re-
   constructed at the intermediate PCE, the PCE must not start its path
   computation until all PCRep messages have been received from all
   neighbor PCEs. However, a complex PCE implementation is required for
   SVEC reconstruction, and waiting mechanisms must be implemented.
   Therefore, it is not recommended to associate path computation
   requests with different PCE chains. This is open issue and is
   currently being discussed in [ID.h-pce] which proposes a
   hierarchical PCE architecture.


6. End-to-end diverse path computation

   In this section, the synchronous approach is provided to compute
   primary and secondary paths simultaneously.

6.1. Disjoint VSPT

   The BRPC procedure constructs a VSPT to inform the enquiring PCE of
   potential paths to the destination node.

   In the end-to-end diverse path computation, diversity (or
   disjointness) information among the potential paths must be
   preserved in the VSPT to ensure end-to-end disjoint path. In order
   to preserve diversity (or disjointness) information, disjoint VSPTs
   are sent in the PCEP PCRep message. The PCReq containing a SVEC
   object with the appropriate diverse flag set would signal that the
   PCE should compute a disjoint VSPT.

   A definition of the disjoint VSPT is a collection of VSPTs, in which
   each VSPT contains a potential set of primary and secondary paths.

   Figure 2 shows an example network. Here, transit nodes in domains
   are not depicted, and PCE1 and PCE2 may be located in border nodes.
   In this network, there are three VSPTs for the potential set of
   diverse paths shown in Figure 3, when the primary path and secondary
   path are requested from S1 to D1. These VSPTs consist of a disjoint


Nishioka & King            Expires August 10, 2010            [Page 12]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   VSPT, which is replied to PCE1. When receiving the disjoint VSPT,
   PCE1 recognizes the disjoint request and disjoint VSPT information.
   PCE1 will then continue to process the request and compute the
   diverse path using the BRPC procedure [RFC5441]. The detail encoding
   for the disjoint VSPT is described in Section 6.2.

              Domain1          Domain2

           +----------+     +----------+

           |   PCE1   |     |   PCE2   |    S1: Source node

           |         BN1---BN4         |    D1: Destination node

           | S1      BN2---BN5      D1 |    BN1-BN6: Border nodes

           |         BN3---BN6         |

           +----------+     +----------+

       Figure 2: Example network for diverse path computation



            VSPT1:            VSPT2:              VSPT3:

              D1                D1                 D1

              / \               / \                / \

           BN4   BN5         BN4   BN6          BN5   BN6

               Figure 2: Disjoint VSPT from PCE2 to PCE1


6.2. Disjoint VSPT encoding

   Encoding for disjoint VSPT follows the definition of PCEP message
   encoding in [RFC5440].

   PCEP PCRep message returns a disjoint VSPT as <path list> for each
   RP object (Request Parameter object). The order of <path> in <path
   list> among <responses> implies a set of primary EROs (Explicit
   Route Objects) and secondary EROs.

   A PCE sending PCRep with a disjoint VSPT can reply with a partial
   disjoint VSPT based on its network operation policy, but the order
   of <path> in <path list> must be aligned correctly.



Nishioka & King            Expires August 10, 2010            [Page 13]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   If confidentiality is required between domains, path key mechanism
   defined in [RFC5520] is used for a disjoint VSPT.

   Detailed disjoint VSPT encoding in Figure 2 is shown below, when a
   primary path and a secondary path are requested from S1 to D1.

       o Request ID #1 (Primary)

           - ERO1 BN4(TE route ID)- ...-D1(TE-Router ID)  [for VSPT1]

           - ERO2 BN4(TE route ID)- ...-D1(TE-Router ID)  [for VSPT2]

           - ERO3 BN5(TE route ID)- ...-D1(TE-Router ID)  [for VSPT3]

       O Request ID #2 (Secondary)

           - ERO4 BN5(TE route ID)- ...-D1(TE-Router ID)  [for VSPT1]

           - ERO5 BN6(TE route ID)- ...-D1(TE-Router ID)  [for VSPT2]

           - ERO6 BN6(TE route ID)- ...-D1(TE-Router ID)  [for VSPT3]



6.3. Path computation procedure

   For end-to-end diverse path computation, the same mode of operation
   as BRPC procedure can be applied (i.e. Step 1 to Step n in Section
   4.2 [RFC5441]). During this procedure, a question is how to
   recognize disjoint VSPTs.

   The recognition of disjoint VSPT is achieved by the PCE sending
   PCReq to its neighbor PCE which maintains the path computation
   request (PCReq) information. If PCReq has one or more SVEC object(s)
   with the appropriate dependency flags, the received PCRep will
   contain the disjoint VSPT. If not, the received VSPT is a normal
   VSPT based on the shortest path computation.

   Note that the PCE will apply a suitable algorithm for computing
   requests with disjoint VSPT. The selection and application of the
   appropriate algorithm is out of scope in this draft.


7. Manageability considerations

   This section describes manageability considerations specified in
   [ID.pce-mngabl-reqs].

7.1. Control of Function and Policy


Nishioka & King            Expires August 10, 2010            [Page 14]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   In addition to [RFC5440], PCEP implementations should allow the PCC
   to be responsible for mapping the requested paths to computation
   requests. The PCC should construct the SVECs to indentify and
   associate SVEC relationships.

7.2. Information and Data Models, e.g. MIB modules

   There are currently no additional parameters for MIB modules. There
   is value in a MIB module that details the SVEC association. This
   work is currently out of scope of this document.

7.3. Liveness Detection and Monitoring

   The associated SVEC in this document allows PCEs to compute optimal
   sets of diverse paths. This type of path computation may require
   more time to obtain its results. Therefore, it is recommended for
   PCEP to support PCE monitoring mechanism specified in [ID.pce-
   monitor].

7.4. Verifying Correct Operation

   [RFC5440] provides the sufficient descriptions for this document. So,
   there are no additional considerations.

7.5. Requirements on Other Protocols and Functional Components

   This document does not require any other protocol and functional
   components.

7.6. Impact on Network Operation

   [RFC5440] provides descriptions for the mechanisms discussed in this
   document.  There is value in considering that large associated SVECs
   will require greater PCE resources, compared to non-associated SVECs.
   Additionally, the sending of large associated SVECs within multiple
   PCReq messages will require more network resources. Solving these
   specific issues is out of scope of this document.


8. Security Considerations

   This document describes the usage of SVEC list, and does not have
   any extensions for PCEP protocol. The security of the procedures
   described in this document depends on PCEP protocol [RFC5440].
   However, a PCE that supports associated SVECs may be open to DoS
   attack from a rogue PCC. A PCE may be made to queue large numbers of
   requests waiting for other requests that will never arrive.
   Additionally a PCE might be made to compute exceedingly complex
   associated SVEC computations. These DoS attacks may be mitigated
   with the use of practical SVEC list limits, as well as:

Nishioka & King            Expires August 10, 2010            [Page 15]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   o Using the same number of simultaneous service provisioning
     would be recommended.

   o Priority-based multi-queuing mechanism in which path
     computation requests with a smaller SVEC list are prioritized
     for path computation processing

   o Specifying which PCCs may request large SVEC associations
     through PCE access policy control.


9. IANA Considerations

   This document has no specific extension for PCEP messages, objects
   and its parameters and does not require any registry assignment.

10. References

10.1. Normative References

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

   [RFC4657] J. Ash and J.L. Le Roux, "Path Computation Element (PCE)
   Communication Protocol Generic Requirements," RFC 4757,
   September 2006.

   [RFC4875] R. Aggarwal, D. Papadimitriou, and S. Yasukawa,
   "Extensions to Resource Reservation Protocol - Traffic
   Engineering (RSVP-TE) for Point-to-Multipoint TE Label
   Switched Paths (LSPs)," RFC4875, May 2007.

   [RFC5440] Ayyangar, A., Farrel, A., Oki, E., Atlas, A., Dolganow A.
   Ikejiri, Y., Kumaki, K., Vasseur, J., and J. Roux, "Path
   Computation Element (PCE) communication Protocol (PCEP),"
   RFC5440, March. 2009.

   [RFC5441] JP. Vasseur, R. Zhang, N. Bitar and JL. Le Roux, "A
   Backward Recursive PCE-based Computation (BRPC) Procedure
   to Compute Shortest Constrained Inter-domain Traffic
   Engineering Label Switched Paths," RFC5441, April 2009.

   [RFC5520] R. Bradford, JP. Vasseur, and A. Farrel, "Preserving
   Topology Confidentiality in Inter-Domain Path Computations
   Using a Path-Key-Based mechanism," RFC5520, April 2009.

   [RFC5521] E. Oki, T. Takeda and A. Farrel, "Extensions to the Path
   Computation Element Communication Protocol (PCEP) for
   Route Exclusions," RFC5521, April 2009.

Nishioka & King            Expires August 10, 2010            [Page 16]

Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010


   [RFC5557] Y. Lee, JL. Le Roux, D. King and E. Oki, "Path Computation
   Element Communication Protocol (PCECP) Requirements and
   Protocol Extensions In Support of Global Concurrent
   Optimization," RFC5557, July 2009.

10.2. Informative References

   [ID.pce-p2mp-ext] Takeda, T., Chaitou M., Le Roux, J.L., Ali Z.,Zhao,
   Q., King, D., "Extensions to the Path Computation Element
   Communication Protocol (PCEP) for Point-to-Multipoint
   Traffic Engineering Label Switched Paths," draft-ietf-pce-
   pcep-p2mp-extensions, work in progress, February, 2010.

   [ID.pce-mngabl-reqs] A. Farrel, "Inclusion of Manageability Sections
   in PCE Working Group Drafts," draft-ietf-pce-
   manageability-requirements, work in progress, July 2009.

   [ID.h-pce] King, D., Farrel, A. "The Application of the Path
   Computation Element Architecture to the Determination of a
   Sequence of Domains in MPLS & GMPLS", draft-king-pce-
   hierarchy-fwk, work in progress, December 2009.


11. Acknowledgements

   The authors would like to thank Adrian Farrel, Julien Meuric and
   Filippo Cugini for their valuable comments.


Authors' Addresses

   Itaru Nishioka
   NEC Corp.
   1753 Shimonumabe,
   Kawasaki, 211-8666,
   Japan

   Phone: +81 44 396 3287
   Email: i-nishioka@cb.jp.nec.com

   Daniel King
   Old Dog Consulting
   United Kingdom

   Phone: +44 7790 775187
   Email: daniel@olddog.co.uk





Nishioka & King            Expires August 10, 2010            [Page 17]
Internet-Draft      draft-ietf-pce-pcep-svec-list-04      February 2010

Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/