\
PCE Working Group                                            Young Lee
Internet Draft                                                 Samsung
Intended Status: Experimental                            Haomian Zheng
Expires: September 2022                                         Huawei
                                                    Daniele Ceccarelli
                                                              Ericsson
                                                              Wei Wang
                                    Beijing Univ. of Posts and Telecom
                                                            Peter Park
                                                                    KT
                                                        Bin Young Yoon
                                                                  ETRI

                                                         March 7, 2022



    PCEP Extension for Distribution of Link-State and TE Information for
                             Optical Networks



                     draft-lee-pce-pcep-ls-optical-11


Abstract

   In order to compute and provide optimal paths, Path Computation
   Elements (PCEs) require an accurate and timely Traffic Engineering
   Database (TED). Traditionally this Link State and TE information has
   been obtained from a link state routing protocol (supporting traffic
   engineering extensions).

   An existing experimental document extends the Path Computation
   Element Communication Protocol (PCEP) with Link-State and Traffic
   Engineering (TE) Information.  This document provides further
   experimental extensions to collect Link-State and TE information for
   optical networks.



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.



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   document authors. All rights reserved.

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Table of Contents


   1. Introduction ................................................ 3
      1.1. Requirements Language .................................. 3
   2. Applicability ............................................... 3
   3. Requirements for PCEP Extension ............................. 4
      3.1. Reachable Source-Destination ........................... 5
      3.2. Optical Latency......................................... 5
   4. PCEP-LS Extensions for Optical Networks ..................... 6
      4.1. Node Attributes TLV .................................... 6
      4.2. Link Attributes TLV .................................... 6
      4.3. PCEP-LS for Optical Network Extension .................. 7
   5. Security Considerations ..................................... 8
   6. IANA Considerations ......................................... 8
      6.1. PCEP-LS Sub-TLV Type Indicators ........................ 8
   7. References .................................................. 9
      7.1. Normative References ................................... 9
      7.2. Informative References ................................. 9


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   Appendix A. Contributor's Address  ............................ 11
   Authors' Addresses ............................................ 11

1. Introduction

   [PCEP-LS] describes an experimental mechanism by which Link State
   (LS) and Traffic Engineering (TE) information can be collected from
   packet networks and shared through the Path Computation Element
   Communication Protocol (PCEP) with a Path Computation Element (PCE).
   This approach is called PCEP-LS and uses a new PCEP message format.

   Problems in the optical networks, such as Optical Transport Networks
   (OTN), is becoming worse due to the growth of the network
   scalability. Such growths are also challenging the requirement of
   memory/storage on each equipment. The introduction of a PCEP-based
   LS helps solving the problem, with equally capability and
   functionalities.

   This document describes an experimental extension to PCEP-LS for use
   in optical networks, and explains how encodings defined in [PCEP-LS]
   can be used in the optical network contexts.

1.1. Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.



2. Applicability

   There are three main applicabilities of the mechanism described in
   this document:

       - Case 1: There is IGP running in optical network but there is a
         need to collect LS and TE resource information at a PCE from
         individual or specific optical nodes more frequently of more
         rapidly than the IGP allows.

            o A PCE may receive full information or an incremental
              update (as opposed to the entire TE information of the
              node/link).




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       - Case 2: There is no IGP running in the optical network and
         there is a need to collect link-state and TE resource
         information from the optical nodes for use by the PCE.


       - Case 3: There is a need to share abstract optical link-state
         and TE information from child PCE to a parent PCE in a
         hierarchical PCE (H-PCE) system per [RFC6805] and [RFC8751].
         Alternatively, this requirement may exist between a Physical
         Network Controller (PNC) and a Multi-Domain Service
         Coordinator (MDSC) in the Abstraction and Control of TE
         Networks (ACTN) architecture [RFC8453].

         Note: The applicability for Case 3 may arise as a consequence
         of Case 1 and Case 2. When TE information changes occur in the
         optical network, this may also affect abstracted TE
         information and thus needs to be updated to the parent
         PCE/MSDC from each child PCE/PNC.



3. Requirements for PCEP Extension


   The key requirements associated with link-state and TE information
   distribution are identified for PCEP and listed in Section 4 of
   [PCEP-LS]. These new functions introduced to PCEP to support
   distribution of link-state (and TE) information are described in
   Section 5 of [PCEP-LS]. Details of PCEP messages and related
   Objects/TLVs are specified in Sections 8 and 9 of [PCEP-LS]. The key
   requirements and new functions specified in [PCEP-LS] are equally
   applicable to optical networks.

   Besides the generic requirements specified in [PCEP-LS], optical
   specific features also need to be considered. As a connection-based
   network, there are specific parameters such as reachability table,
   optical latency, wavelength consistency, and some other parameters
   that need to be included during the topology collection. Without
   these restrictions, the path computation may be inaccurate or
   infeasible for deployment, therefore these information MUST be
   included in the PCEP.

   The procedure for using the optical parameters is described in
   following sections.





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       3.1. Reachable Source-Destination

   The reachable source-destination node pair indicates that there are
   some OCh paths between two nodes.  The reachability is restricted by
   impairment, wavelength consistency and so on. This information is
   necessary at the PCE to ensure that the path computed between source
   node and destination node is feasible. In this scenario, the PCE is
   responsible for computing how many OCh paths are available to set up
   connections between source and destination node.  Moreover, if a set
   of optical wavelengths is indicated in the path computation request,
   the PCE also determines whether a wavelength from the set of
   preselected optical wavelengths is available for the source-
   destination pair connection.

   To enable the PCE to complete the above functions, the reachable
   relationship and OMS link information need to be reported to the
   PCE.  Once the PCE detects that any wavelength is available, the
   corresponding OMS link is marked as a candidate link in the optical
   network, which can then be used for path computation in the future.

   Moreover, in a hierarchical PCE architecture, the information above
   needs to be reported from child PCE to parent PCE, which acts as a
   service coordinator.

       3.2. Optical Latency

   It is the usual case that the PCC indicates the latency when
   requesting the path computation. In optical networks the latency is
   a very sensitive parameter and there is stricter requirement on
   latency. Given the number of OCh paths between source-destination
   nodes, the PCE also need to determine how many OCh path satisfy the
   indicated latency threshold.

   There is usually an algorithm running on the PCE to guarantee the
   performance of the computed path. During the computation, the delay
   factor may be converted into a kind of link weight. After the
   algorithm provides the candidate paths between the source and
   destination nodes, the PCE selects the best path by computing the
   total path propagation delay.

   Optical PCEs contain optimization algorithms, e.g., shortest path
   algorithm, to select the best-performing path.







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4. PCEP-LS Extensions for Optical Networks

   This section provides the additional PCEP-LS extensions necessary to
   support optical networks. All Objects/TLVs defined in [PCEP-LS] are
   applicable to optical networks.

       4.1. Node Attributes TLV

   The Node-Attributed TLV is defined in Section 9.3.9.1 of [PCEP-LS].
   This TLV is applicable for LS Node Object-Type as defined in [PCEP-
   LS].

   This TLV contains a number of Sub-TLVs.  [PCEP-LS] defines that any
   Node-Attribute defined for BGP-LS [BGP-LS] can be used as a Sub-TLV
   of the PCEP Node-Attribute TLV.  BGP-LS does not support optical
   networks, so the Node-Attribute Sub-TLVs shown below are defined in
   this document for use in PCEP-LS for optical networks.

   TBD1 The Connectivity Matrix Sub-TLV is used as defined in
         [RFC7579].

   TBD2 The Resource Block Information Sub-TLV is used as defined in
         [RFC7688].

   TBD3 The Resource Block Accessibility Sub-TLV is used as defined in
         [RFC7688].

   TBD4 The Resource Block Wavelength Constraint Sub-TLV is used as
         defined in [RFC7688].

   TBD5 The Resource Block Pool State Sub-TLV is used as defined in
         [RFC7688].

   TBD6 The Resource Block Shared Access Wavelength Availability
         Sub-TLV is used as defined in [RFC7688].

       4.2. Link Attributes TLV

   The Link-Attributes TLV is defined in Section 9.3.9.2 of [PCEP-LS].
   This TLV is applicable for the LS Link Object-Type as defined in
   [PCEP-LS].

   This TLV contains a number of Sub-TLVs.  [PCEP-LS] defines that any
   Node-Attribute defined for BGP-LS [BGP-LS] can be used as a Sub-TLV
   of the PCEP Link-Attribute TLV.  BGP-LS does not support optical
   networks, so the Link-Attribute Sub-TLVs shown below are defined in
   this document for use in PCEP-LS for optical networks.


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   TBD7 The ISCD Sub-TLV is used to describe the Interface Switching
         Capability Descriptor as defined in [RFC4203].

   TBD8 The OTN-TDM SCSI Sub-TLV is used to describe the Optical
         Transport Network Time Division Multiplexing Switching
         Capability Specific Information as defined in [RFC4203] and
         [RFC7138].

   TBD9 The WSON-LSC SCSI Sub-TLV is used to describe the Wavelength
         Switched Optical Network Lambda Switch Capable Switching
         Capability Specific Information as defined in [RFC4203] and
         [RFC7688].

   TBD10 The Flexi-grid SCSI Sub-TLV is used to describe the Flexi-grid
         Switching Capability Specific Information as defined in
         [RFC8363].

   TBD11 The Port Label Restriction Sub-TLV is used as defined in
         [RFC7579], [RFC7580], and [RFC8363].

       4.3. PCEP-LS for Optical Network Extension

   This section provides additional PCEP-LS extension necessary to
   support the optical network parameters discussed in Sections 3.1 and
   3.2.

   Collection of link state and TE information is necessary before the
   path computation processing can be done.  The procedure can be
   divided into: 1) link state collection by receiving the
   corresponding topology information in periodically; 2) path
   computation on the PCE, triggered by receiving a path computation
   request message from a PCC, and completed by transmitting a path
   computation reply with the path computation result, per [RFC4655].

   For OTN networks, maximum bandwidth available may be per ODU 0/1/2/3
   switching level or aggregated across all ODU switching levels (i.e.,
   ODUj/k).

   For Wavelength Switched Optical Networks (WSON) , Routing and
   Wavelength Assignment (RWA) information collected from Network
   Elements (Nes) would be utilized to compute light paths. The list of
   information collected can be found in [RFC7688]. More specifically,
   the maximum bandwidth available may be per lambda/frequency level


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   (OCh) or aggregated across all lambda/frequency levels. Per OCh
   level abstraction gives more detailed data to the P-PCE at the
   expense of more information processing. Either the OCh-level or the
   aggregated level abstraction in the RWA constraint (i.e., wavelength
   continuity) needs to be taken into account by the PCE during path
   computation. Resource Block Accessibility (i.e., wavelength
   conversion information) in [RFC7688] needs to be taken into account
   in order to guarantee the reliability of optical path computation.

5. Security Considerations

   This document extends PCEP for LS (and TE) distribution  in optical
   networks by including a set of Sub-TLVs to be carried in existing
   TLVs of existing messages.  Procedures and protocol extensions
   defined in this document do not affect the overall PCEP security
   model (see [RFC5440] and [RFC8253]). The PCE implementation SHOULD
   provide mechanisms to prevent strains created by network flaps and
   amount of LS (and TE) information as defined in [PCEP-LS].  Thus,
   any mechanism used for securing the transmission of other PCEP
   message SHOULD be applied here as well.  As a general precaution, it
   is RECOMMENDED that these PCEP extensions only be activated on
   authenticated and encrypted sessions belonging to the same
   administrative authority.

6. IANA Considerations

   This document requests IANA actions to allocate code points for the
   protocol elements defined in this document.

       6.1. PCEP-LS Sub-TLV Type Indicators

   PCEP-LS] requests IANA to create a registry of "PCEP-LS Sub-TLV Type
   Indicators".  IANA is requested to make the following allocations
   from this registry using the range 1 to 255.


   +-----------+--------------------------------------------------
   |  Sub-TLV  | Meaning
   +-----------+--------------------------------------------------
   |    TBD1   | Connectivity Matrix
   |    TBD2   | Resource Block Information
   |    TBD3   | Resource Block Accessibility
   |    TBD4   | Resource Block Wavelength Constraint
   |    TBD5   | Resource Block Pool State
   |    TBD6   | Resource Block Shared Access Wavelength Available
   |    TBD7   | ISCD
   |    TBD8   | OTN-TDM SCSI


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   |    TBD9   | WSON-LSC SCSI
   |    TBD10  | Flexi-grid SCSI
   |    TBD11  | Port Label Restriction



7. References

       7.1. Normative References

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

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
             Engineering", RFC 5305, October 2008.

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

   [RFC7688] Lee, Y., Ed., and G. Bernstein, Ed., "GMPLS OSPF
             Enhancement for Signal and Network Element Compatibility
             for Wavelength Switched Optical Networks", RFC 7688,
             November 2015.

   [RFC8174] B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119
             Key Words", RFC 8174, May 2017.

       7.2. Informative References

   [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
             (TE) Extensions to OSPF Version 2", RFC 3630, September
             2003.

   [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
             Support of Generalized Multi-Protocol Label Switching
             (GMPLS)", RFC 4203, October 2005.

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

   [RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
             in Support of Generalized Multi-Protocol Label Switching
             (GMPLS)", RFC 5307, October 2008.





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   [RFC7752] Gredler, H., Medved, J., Previdi, S., Farrel, A., and
             S.Ray, "North-Bound Distribution of Link-State and TE
             information using BGP", RFC 7752, March 2016.

   [S-PCE-GMPLS] X. Zhang, et. al, "Path Computation Element (PCE)
             Protocol Extensions for Stateful PCE Usage in GMPLS-
             controlled Networks", draft-ietf-pce-pcep-stateful-pce-
             gmpls, work in progress.

   [RFC7399] A. Farrel and D. king, "Unanswered Questions in the Path
             Computation Element Architecture", RFC 7399, October 2015.

   [RFC8453] D.Ceccarelli, and Y. Lee (Editors), "Framework for
             Abstraction and Control of TE Networks", RFC453, August,
             2018.

   [RFC6805] A. Farrel and D. King, "The Application of the Path
             Computation Element Architecture to the Determination of a
             Sequence of Domains in MPLS and GMPLS", RFC 6805, November
             2012.

   [PCEP-LS] D. Dhody, Y. Lee and D. Ceccarelli "PCEP Extension for
             Distribution of Link-State and TE Information.", draft-
             dhodylee-pce-pcep-ls, work in progress, July, 2020

   [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
             Extensions for Stateful PCE", RFC8231, September 2017.

   [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., Dhody, D.,
             "PCEPS: Usage of TLS to Provide a Secure Transport for the
             Path Computation Element Communication Protocol (PCEP)",
             RFC8253, October 2017.

   [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
             Extensions for PCE-initiated LSP Setup in a Stateful PCE
             Model", RFC8281, December 2017.

   [RFC8751] D. Dhody, Y. Lee and D. Ceccarelli, "Hierarchical Stateful
             Path Computation Element (PCE)", RFC8751, March 2020.

   [RFC8363] X. Zhang, H. Zheng, R. Casellas, O. Gonzalez de Dios, D.
             Ceccarelli, "GMPLS OSPF Extensions in support of Flexi-
             grid DWDM networks", RFC8363, May 2018.






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Appendix A. Contributor's Address

   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka 560066
   India
   Email: dhruv.ietf@gmail.com


Authors' Addresses


   Young Lee
   Samsung
   Email: younglee.tx@gmail.com

   Haomian Zheng
   Huawei Technologies Co., Ltd.
   Email: zhenghaomian@huawei.com


   Daniele Ceccarelli
   Ericsson
   Torshamnsgatan,48
   Stockholm
   Sweden
   EMail: daniele.ceccarelli@ericsson.com

   Wei Wang
   Beijing University of Posts and Telecom
   No. 10, Xitucheng Rd. Haidian District, Beijing 100876, China
   Email: weiw@bupt.edu.cn

    Peter Park
  KT
  Email: peter.park@kt.com

   Bin Yeong Yoon
   ETRI
   Email: byyun@etri.re.kr



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