



PCE Working Group                                                 L. Han
Internet-Draft                                                  H. Huang
Intended status: Standards Track                                 M. Wang
Expires: 2 September 2026                                           CMCC
                                                                L. Zhang
                                                                  Huawei
                                                                 J. Zhou
                                                                     ZTE
                                                            1 March 2026


PCEP LS Extensions for Fine Granularity Metro Transport Network (fgMTN)
                Topology Resource Information Reporting
                  draft-han-pce-ls-fgmtn-reporting-00

Abstract

   This document extends PCEP-LS by defining several new sub-TLVs for
   the LS object to report the fgMTN topology resource information,
   which includes timeslot occupation status of links and the
   relationship between the FGU client and the occupied timeslots.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 2 September 2026.

Copyright Notice

   Copyright (c) 2026 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 (https://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



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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  OPEN Object . . . . . . . . . . . . . . . . . . . . . . .   3
       2.1.1.  LS Capability TLV . . . . . . . . . . . . . . . . . .   3
     2.2.  LS Object . . . . . . . . . . . . . . . . . . . . . . . .   3
       2.2.1.  Parent NRP ID Sub-TLV . . . . . . . . . . . . . . . .   4
       2.2.2.  Sub-Slot BitMap Sub-TLV . . . . . . . . . . . . . . .   4
       2.2.3.  FGU Client Sub-Slot Bitmap Relationship Sub-TLV . . .   5
       2.2.4.  FGU Client Sub-Slot Relationship Sub-TLV  . . . . . .   7
   3.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   MTN(Metro Transport Network) [ITU-T_G.8310] is a new generation of
   transport network technology system defined by ITU-T.  MTN integrates
   packet and TDM technologies, enabling compatibility with Ethernet
   protocol stacks while meeting differentiated requirements of the 5G
   era, such as hard isolation, low latency, and high reliability, thus
   further enhancing the bearer capability of 5G networks.  On this
   basis, the fgMTN technology [ITU-T_G.8312.20]incorporates fine-
   grained slicing into the MTN architecture, providing a low-cost,
   refined, hard-isolated, and fine-grained bearer channels.  The fgMTN
   technology further refines the granularity of hard slicing from 5
   Gbit/s to 10 Mbit/s, meeting the differentiated service bearer
   requirements of vertical industry applications and private line
   services, such as small bandwidth, high isolation, and high security.
   The fgMTN technology is one of the means to realize network resource
   partitions(NRP) [RFC9543].

   fgMTN uses the management and control system to perform centralized
   path computation.  However, the current MTN management and control
   standard [ITU-T_G.8350] only defines the functions of topology and
   resource collection and does not specify specific protocols.





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   [RFC5440] describes the Path Computation Element Communication
   Protocol (PCEP).  PCEP defines the communication between a Path
   Computation Client (PCC) and a Path Computation Element (PCE), or
   between PCEs.  PCEP-LS [I-D.ietf-pce-pcep-ls] extends PCEP to enable
   the collection of link-state and TE information from networks and
   sharing with PCE by extending a new LS Report message.  Therefore,
   the PCEP-LS can be extended to support the reporting of fgMTN
   topology resources.

   This document extends PCEP-LS by defining several new sub-TLVs for
   the LS object to report the fgMTN topology resource information,
   which includes timeslot ccupation status of links and the
   relationship between the FGU client and the occupied timeslots.

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.  Protocol Extensions

2.1.  OPEN Object

2.1.1.  LS Capability TLV

   [I-D.ietf-pce-pcep-ls] defines LS-CAPABILITY TLV for use in the OPEN
   Object for link-state (and TE) distribution via PCEP capability
   advertisement.

   This document defines a new flag in the flags field of the LS-
   CAPABILITY TLV to indicate the support of fgMTN resource information
   reporting.

   Bit M (fgMTN state collection, 1-bit): if set to 1 by a PCC, the M
   Flag indicates that the PCC allows the reporting of fgMTN resource
   information learned via other means like LLDP; if set to 1 by a PCE,
   the M Flag indicates that the PCE is capable of receiving fgMTN
   resource information.

2.2.  LS Object

   The LS (link-state) object is defined by [I-D.ietf-pce-pcep-ls], it
   MUST be carried within LSRpt messages.  The LS object contains a set
   of TLVs used to specify the target node's or link's information.




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   [I-D.ietf-pce-pcep-ls] also defines the Link Descriptors TLV, it
   contains Link Descriptors for each link.  The value of it contains
   one or more Link Descriptor Sub-TLVs.

   This document defines four kind of Link Descriptor Sub-TLVs to
   describe the fgMTN resource information.

2.2.1.  Parent NRP ID Sub-TLV

   The Parent NRP ID sub-TLV indicates the NRP ID that the link belongs
   to.  This sub-TLV is an optional sub-TLV MAY be included in the Link
   Descriptors TLV.

   At most one instance of this sub-TLV can be included in the Link
   Descriptors TLV.  The format of this sub-TLV is shown in Figure 1.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            NRP-ID                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: Parent NRP ID Sub-TLV

   where:

   Type: TBD1, needs to be allocated by IANA.

   Length: the length of NRP-ID, equals to 4.

   NRP-ID: 4-bit length, the value of NRP-ID is the slice ID of the
   service-layer interface (MTN client or GE/10GE interface) of a fine-
   grained interface.  If t the information does not exist on the
   device, the default value 0xFFFFFFFF SHOULD be filled.

2.2.2.  Sub-Slot BitMap Sub-TLV

   The sub-slot bitmap sub-TLV indicates the timeslot's occupation
   status of all FGU clients in the link.  This sub-TLV is an optional
   sub-TLV MAY be included in the Link Descriptors TLV.  At most one
   instance of this sub-TLV can be included in the Link Descriptors TLV.
   The format of this sub-TLV is shown in Figure 2.







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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /                  Sub-slot bitmap (variable)                   /
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 2: Parent NRP ID Sub-TLV

   where:

   Type: TBD2, needs to be allocated by IANA.

   Length: the length of sub-slot bitmap, variable.

   Sub-slot bitmap: variable, indicates the occupation state of all the
   timeslots of the link, each bit represents a timeslot.  If the last
   bits are all zeros, the padding can be omitted.

2.2.3.  FGU Client Sub-Slot Bitmap Relationship Sub-TLV

   The FGU Client Sub-Slot Bitmap Relationship sub-TLV indicates the
   relationship between the occupied timeslots(expressed by bitmap) and
   corresponding FGU Client.

   This sub-TLV is an optional sub-TLV MAY be included in the Link
   Descriptors TLV.  More than one instance of this sub-TLV can be
   included in the Link Descriptors TLV.  The format of this sub-TLV is
   shown in Figure 3.



















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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    FGU Client Port index                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     FGU Client number         |   Reserved    | Start Position|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /               Forward fg Channel index (22 Bytes)             /
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /               Backward fg Channel index (22 Bytes)            /
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /                  Sub-slot bitmap (variable)                   /
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 3: FGU Client Sub-Slot BitMap RelationShip Sub-TLV

   where:

   Type: TBD3, needs to be allocated by IANA.

   Length: the length of value field, variable.

   FGU Client Port index: 4-byte length, the local FGU client port
   identifier allocated by the device itself, which is unique within a
   network device.  The value ranges from 1 to 0xFFFFFFFF.  The value 0
   indicates an invalid value.

   FGU Client number: 2-byte length, the FGU client identifier
   negotiated by the source and destination device, which is unique
   within a MTN client.  The value ranges from 1 to 1022.  The value 0
   indicates not used, and the value 1023 is reserved.

   Start Position: 1-byte length, the start position of the timeslots
   occupied by the current FGU client.  It is expressed in bytes.  The
   timeslots are arranged in the order of timeslots 0 to 959.  The value
   of this field ranges from 0 to 119.

   Forward fg Channel index: 22-byte length, forward fg channel
   identifier.  It is a unique channel ID on the entire network, which
   is identified by the combination of the source device's MPLS LSR ID



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   (16 bytes, device IPv4 or IPv6 address), fg Channel ID (4 bytes,
   allocated by the management and control system, unique within the
   source node), and LSP ID (2 bytes, allocated by the management and
   control system, used to distinguish the original path from the
   rerouting path).

   Backward fg Channel index: 22-byte length, backward fg channel
   identifier.  It is a unique channel ID on the entire network, which
   is identified by the combination of the following information: MPLS
   LSR ID (16 bytes, IPv4 or IPv6 address of the device) of the reverse
   source, fg Channel ID (4 bytes, allocated by the management and
   control system, unique within the source node), and LSP ID (2 bytes,
   allocated by management and control system, used to distinguish the
   original path from the rerouting path).

   Sub-slot bitmap: variable, indicates the occupation state of all the
   sub-slots of the FGU.  It starts from the start position.  If the
   last bits are all zeros, the padding can be omitted.

2.2.4.  FGU Client Sub-Slot Relationship Sub-TLV

   The FGU Client Sub-Slot Bitmap Relationship sub-TLV indicates the
   relationship between the occupied timeslots(expressed by enumeration
   value) and FGU Client.  This sub-TLV is an optional sub-TLV MAY be
   included in the Link Descriptors TLV.  More than one instance of this
   sub-TLV can be included in the Link Descriptors TLV.  The format of
   this sub-TLV is shown in Figure 4:
























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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       FGU Client index                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     FGU Client number         |   Reserved    | Start Position|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /               Forward fg Channel index (22 Bytes)             /
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /               Backward fg Channel index (22 Bytes)            /
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /                   Sub-Slot IDs (variable)                     /
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 4: FGU Client Sub-Slot Relationship Sub-TLV

   where:

   Type: TBD4, needs to be allocated by IANA.

   Length: the length of value field, variable.

   FGU Client Port index: 4-byte length, the local FGU client port
   identifier allocated by the device itself, which is unique within a
   network device.  The value ranges from 1 to 0xFFFFFFFF.  The value 0
   indicates an invalid value.

   FGU Client number: 2-byte length, the FGU client identifier
   negotiated by the source and destination device, which is unique
   within a MTN client.  The value ranges from 1 to 1022.  The value 0
   indicates not used, and the value 1023 is reserved.

   Start Position: 1-byte length, the start position of the timeslots
   occupied by the current FGU client.  It is expressed in bytes.  The
   timeslots are arranged in the order of timeslots 0 to 959.  The value
   of this field ranges from 0 to 119.

   Forward fg Channel index: 22-byte length, forward fg channel
   identifier.  It is a unique channel ID on the entire network, which
   is identified by the combination of the source device's MPLS LSR ID



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   (16 bytes, device IPv4 or IPv6 address), fg Channel ID (4 bytes,
   allocated by the management and control system, unique within the
   source node), and LSP ID (2 bytes, allocated by the management and
   control system, used to distinguish the original path from the
   rerouting path).

   Backward fg Channel index: 22-byte length, backward fg channel
   identifier.  It is a unique channel ID on the entire network, which
   is identified by the combination of the following information: MPLS
   LSR ID (16 bytes, IPv4 or IPv6 address of the device) of the reverse
   source, fg Channel ID (4 bytes, allocated by the management and
   control system, unique within the source node), and LSP ID (2 bytes,
   allocated by management and control system, used to distinguish the
   original path from the rerouting path).

   Sub-slot IDs: Variable length, indicates the enumerated value of the
   sub-slots occupied by the current FGU client.  Each sub-slot ID is
   represented by 2 bytes.  The number of sub-slot ID ranges from 0 to
   959.

3.  Procedures

   TBD.

4.  Security Considerations

   TBD.

5.  IANA Considerations

   [I-D.ietf-pce-pcep-ls] requests IANA to create a "PCEP-LS Sub-TLV
   Types" sub-registry for the sub-TLVs carried in the PCEP-LS TLV.
   This document requests IANA to make the following allocations from
   this sub-registry.

















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          +=======+============================+===============+
          | Value | Description                | Reference     |
          +=======+============================+===============+
          | TBD1  | Parent NRP ID Sub-TLV      | This document |
          +-------+----------------------------+---------------+
          | TBD2  | Sub-Slot Bitmap Sub-TLV    | This document |
          +-------+----------------------------+---------------+
          | TBD3  | FGU Client Sub-Slot Bitmap | This document |
          |       | Relationship Sub-TLV       |               |
          +-------+----------------------------+---------------+
          | TBD4  | FGU Client Sub-Slot        | This document |
          |       | Relationship Sub-TLV       |               |
          +-------+----------------------------+---------------+

                       Table 1: IANA Considerations

6.  Acknowledgments

   TBD.

7.  Normative References

   [ITU-T_G.8312.20]
              ITU-T, "ITU-T G.8312.20:Overview of fine grain MTN;
              01/2024",  https://www.itu.int/rec/T-REC-G.8312.20,
              January 2024.

   [ITU-T_G.8310]
              ITU-T, "ITU-T G.8310: Architecture of the metro transport
              network; 01/2024",  https://www.itu.int/rec/T-REC-G.8310,
              March 2025.

   [ITU-T_G.8350]
              ITU-T, "ITU-T G.8350: Management and control of metro
              transport networks; 11/2022",  https://www.itu.int/rec/T-
              REC-G.8350, November 2022.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.





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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, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC9543]  Farrel, A., Ed., Drake, J., Ed., Rokui, R., Homma, S.,
              Makhijani, K., Contreras, L., and J. Tantsura, "A
              Framework for Network Slices in Networks Built from IETF
              Technologies", RFC 9543, DOI 10.17487/RFC9543, March 2024,
              <https://www.rfc-editor.org/info/rfc9543>.

   [I-D.ietf-pce-pcep-ls]
              Dhody, D., Peng, S., Lee, Y., Ceccarelli, D., Wang, A.,
              and G. S. Mishra, "PCEP extensions for Distribution of
              Link-State and TE Information", Work in Progress,
              Internet-Draft, draft-ietf-pce-pcep-ls-04, 14 October
              2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
              pce-pcep-ls-04>.

Authors' Addresses

   Liuyan Han
   China Mobile
   No.32 Xuanwumen west street
   Beijing
   100053
   China
   Email: hanliuyan@chinamobile.com


   Haibin Huang
   China Mobile
   No.32 Xuanwumen west street
   Beijing
   100053
   China
   Email: huanghaibin@chinamobile.com


   Minxue Wang
   China Mobile
   No.32 Xuanwumen west street
   Beijing
   100053
   China
   Email: wangminxue@chinamobile.com






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   Li Zhang
   Huawei
   Beiqing Road
   Beijing
   China
   Email: zhangli344@huawei.com


   Jin Zhou
   ZTE Corporation
   Shenzhen
   China
   Email: zhou.jin6@zte.com.cn






































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