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Path Computation and Control Extention Requirements for Fine-Granularity Transport Network

Document Type Active Internet-Draft (individual)
Authors Liuyan Han , Haomian Zheng , Minxue Wang , Yang Zhao
Last updated 2024-03-04
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PCE Working Group                                                 L. Han
Internet-Draft                                              China Mobile
Intended status: Standards Track                                H. Zheng
Expires: 5 September 2024                            Huawei Technologies
                                                                 M. Wang
                                                                 Y. Zhao
                                                            China Mobile
                                                            4 March 2024

Path Computation and Control Extention Requirements for Fine-Granularity
                           Transport Network


   This document focuses on the requirements for path computation and
   control of the fine-granularity transport network.  It provides the
   general context of the use cases of path computation and the
   considerations on the requirements of PCE extension in such fine-
   granularity transport network.

Status of This Memo

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   This Internet-Draft will expire on 5 September 2024.

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   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Path Computation Requirements in Fine-grain Transport
           Network . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Use Cases of Fine-grain Path Computation  . . . . . . . . . .   5
   6.  Requirements of PCE Extension for Fine-grain Transport
           Network . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  PCEP Extension for Fine-grain Transport Network . . . . . . .   6
   8.  Manageability Consideration . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   11. Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   With the proposal of new service demand, the technology of the
   transport network is constantly developing.  TDM based Optical
   Transport Network (OTN) and Metro Transport Network (MTN)
   technologies are both moving towards fine- grain hard slices.  The
   vertical industries and dedicated line services have higher
   requirements on isolation, security and reliability but with smaller
   bandwidth.  Fine-grain TDM technology can provide the flexible
   N*10Mbps bandwidth for these connections.

   ITU-T has a series of recommendations for fgOTN (fine grain OTN ) and
   fgMTN (fine grain MTN).  The fgOTN overview is defined in
   [ITU-T_G.709.20], fgOTN layer architecture is defined in
   [ITU-T_G.872], fgOTN Interface and server adaptation is defined in
   [ITU-T_G.709], fgOTN equipment is defined in [ITU-T_G.798], fgOTN
   synchronization is defined in [ITU-T_G.8251], fgOTN management
   requirementsis defined in [ITU-T_G.874] and protocol-neutral
   information model is defined in [ITU-T_G.875].  The fgMTN overview is
   defined in[ITU-T_G.8312.20], fgMTN layer architecture is defined in
   [ITU-T_G.8310], fgMTN interface is defined in [ITU-T_G.8312], fgMTN
   equipment is defined in [ITU-T_G.8321], fgMTN synchronization is
   defined in [] , and management requirement and
   information model is defined in [ITU-T_G.8350].  Both the fgOTN and
   fgMTN protection are defined in [ITU-T_G.808.4].

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   The new fine-grain transport technology will significantly increase
   the number of path connections in the network compared to the
   traditional connections based on optical wavelength or ODUk with
   larger bandwidth.  For the future massive fine-grain channel
   connections, how to effectively perform end-to-end path computation
   and control will be an important technical topic.

   The architecture of a Path Computation Element (PCE)-based model has
   been presented in [RFC4655].  It discusses PCE-based implementations
   including composite, external, and multiple PCE path computation.
   [RFC8779]addresses the extensions required for GMPLS applications and
   routing requests, for example, for Optical Transport Networks (OTNs)
   and Wavelength Switched Optical Networks (WSONs).  Due to the new
   features of fine-grain technology, PCE may need to be extended.

   This document focuses on the requirements for path computation and
   control of the fine-grain transport network.  Section 3 provides the
   general context of the use cases of path computation.  Section 4
   provides the considerations on the requirements of PCE extension in
   such fine-grain transport network.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

3.  Terminology


      A domain, as defined in [RFC4655], is "any collection of network
      elements within a common sphere of address management or path
      computation responsibility".  Specifically, within this document,
      we mean a part of an operator's network under common management
      (i.e., under shared operational management using the same
      instances of a tool and the same policies).  Network elements are
      often grouped into domains based on technologies, vendor profiles,
      or geographic proximity.


      Fine Grain


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      Metro Transport Network


      Optical Transport Network

4.  Path Computation Requirements in Fine-grain Transport Network

   Compared to traditional optical networks, fine-grain transport
   networks require more quantity, faster, and more flexible path set-up
   and removing capabilities.  The path computation architecture should
   be reliable, scalable and efficient to facilitate the configuration
   of a large amount of fine-granularity channel connections.

      +-----------------------+           +------------------------+
      |         Domain A      |           |        Domain B        |
    +-+-+   +--+    +--+     ++-+       +-++    +--+    +--+     +-+-+
    +-+-+   +--+    +--+     ++-+       +-++    +--+    +--+     +-+-+
      |                       |           |                        |
      +-----------------------+           +------------------------+
      ^                                                            ^
      |                                                            |
      +-----------------E2E fine-grain connection----------------+

           Figure 1: Scenario of E2E fine-grain connection

   o The number of fine-grain TDM channels will significantly increase:

      FgOTN and fgMTN support 10Mbit/s level tributary slots
      granularity.  One ODU2 channel can support up to 952 fgOTN
      connections.  One 5Gbps MTN channel can support up to 480 fgMTN
      connections.  For transport devices with a switching capacity of
      several Tbps, they can support fine-grain channel connections of
      tens of thousands or even tens of thousands.  Therefore, for the
      network, the number of connections throughout the entire network
      will significantly increase.

   o According to service requirements, fine-grain paths may change
   frequently and dynamically:

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      One fine-grain channel can carry and correspond to a certain CBR
      or Ethernet service, rather than serving as a large optical
      channel.  When the services appear or end, or its bandwidth
      changes, or the destination address changes, they will cause
      changes in fine-grain channels.  Therefore, compared to serving as
      an optical bandwidth channel for the routers, the fine-granularity
      channels serve directly as service channels, which are more likely
      to change.

5.  Use Cases of Fine-grain Path Computation

   To address the massive fine-grain path computation issues, it is
   necessary to combine centralized control systems and distributed
   control protocols.  On the one hand, a centralized control system is
   used to calculate the global optimal routing and develop resource
   scheduling strategies.  On the other hand, distributed control
   protocols between devices are used to perform operations such as
   cross connection configuration and time slot occupation assignment.

   The applications of fine-grain path computation and related
   capabilities at least include:

   o Fine-grain path set-up:

      The control system calculates service routing in a centralized way
      and sends messages to the source node.  Then, the connection is
      established between devices through connection control signaling.
      The end-to-end fine-grain connections may cross one or more

   o Fine-grain resource management:

      The topology and resource information of fine-grain devices and
      slots need to be collected and reported, so that the centralized
      system can calculate new routes based on this information and
      allocate slot resources for the new connections.

   o Fine-grain path update:

      During the connection, fine-grain channels can undergo hitless
      bandwidth adjustment.  When channel bandwidth increases or
      decreases, time slots need to be added or removed.  It is needed
      to control and update the existing path parameter.

   o Fine-grain path removal:

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      When the service no longer needs this connection, it is necessary
      to remove this fine-grain channel and release the corresponding

   o Service awareness and mapping:

      In order to accurately match the fine-grain service requirements,
      the service awareness and mapping function for fine-grain
      transport network have been defined
      in[I-D.liu-ccamp-optical2cloud-problem-statement].  The PE device
      learns and identifies the packet header carried by client services
      (including source and destination MAC or IP addresses etc).  Then
      it reports the identified client services to the control system.
      The control system selects or creates connection(s) acorrding to
      service requirements, and configures the mapping between service
      and connection(s).

6.  Requirements of PCE Extension for Fine-grain Transport Network

   The centralized computation model of PCE architecture seems to be
   suitable for the fine-grain transport network, while the PCEP (PCE
   communication protocol) needs to be extended to meet the fine-grain
   transport requirements.

   The path calculation request/reply message from the PCC or the PCE
   must contain the information specifying appropriate fine-grain
   channel attributes, including the fine-grain switching capability/
   type, the fine-grain server layer type, the fine-grain time slots,
   the fine-grain client ID, end-to-End fine-granularity path protection
   type, etc.

   The protocol and signaling should support the application of fine-
   grain path set-up/update/removal and resource management.

7.  PCEP Extension for Fine-grain Transport Network

   Fine-grain path set-up/adjustment,service awareness and mapping and
   fine- grain resource management may be invovled in PCEP extensions.
   The specific extentions will continue to apply in the future.

8.  Manageability Consideration


9.  Security Considerations


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10.  IANA Considerations


11.  Normative References

              Liu, S., Zheng, H., Guo, A., Zhao, Y., and D. King,
              "Problem Statement and Gap Analysis for Connecting to
              Cloud DCs via Optical Networks", Work in Progress,
              Internet-Draft, draft-liu-ccamp-optical2cloud-problem-
              statement-05, 11 October 2023,

              ITU-T, "ITU-T G.709: Interfaces for the optical transport

              ITU-T, "ITU-T G.709.20: Overview of fine grain
              OTN;",  Work in progress.

              ITU-T, "ITU-T G.798: Characteristics of optical transport
              network hierarchy equipment functional

              ITU-T, "ITU-T G.808.4: Linear protection for fgMTN and
              fgOTN;",  Work in progress.

              ITU-T, "ITU-T G.8251: The control of jitter and wander
              within the optical transport network

              ITU-T, "ITU-T G.8310: Architecture of the metro transport
              network; 01/2024",  Work in progress, January 2024.

              ITU-T, "ITU-T G.8312:Interfaces for metro transport
              networks; 01/2024",,
              January 2024.

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              ITU-T, "ITU-T G.8312.20:Overview of fine grain MTN;
              January 2024.

              ITU-T, "ITU-T G.8321:Characteristics of metro transport
              network equipment functional

              ITU-T, "ITU-T G.8350: Management and Control of metro
              transport networks;",

              ITU-T, "ITU-T G.872: Architecture of the optical transport

              ITU-T, "ITU-T G.874: Management aspects of optical
              transport network elements;",

              ITU-T, "ITU-T G.875: Optical transport network: Protocol-
              neutral management information model for the network
              element view;",

              ITU-T, "ITU-T aspects of metro
              transport network",  Work in progress.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8779]  Margaria, C., Ed., Gonzalez de Dios, O., Ed., and F.
              Zhang, Ed., "Path Computation Element Communication
              Protocol (PCEP) Extensions for GMPLS", RFC 8779,
              DOI 10.17487/RFC8779, July 2020,

Authors' Addresses

   Liuyan Han
   China Mobile
   No.32 Xuanwumen west street
   Beijing, 100053

   Haomian Zheng
   Huawei Technologies
   H1, Huawei Xiliu Beipo Village, Songshan Lake.
   Guangdong, 523808

   Minxue Wang
   China Mobile
   No.32 Xuanwumen west street
   Beijing, 100053

   Yang Zhao
   China Mobile
   No.32 Xuanwumen west street
   Beijing, 100053

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