Architecture Discussion on SRv6 Mobile User plane
draft-ietf-dmm-srv6mob-arch-02

DMM Working Group                                              T. Kamata
Internet-Draft                                                   J. Horn
Intended status: Informational                       Cisco Systems, Inc.
Expires: 6 March 2026                                           L. Jalil
                                                                 Verizon
                                                                W. Cheng
                                                            China Mobile
                                                                M. Kohno
                                                         Keio University
                                                        2 September 2025

           Architecture Discussion on SRv6 Mobile User plane
                     draft-ietf-dmm-srv6mob-arch-02

Abstract

   This document describes the solution approach and its architectural
   benefits of transforming mobile session information into routing
   information, leveraging segment routing capabilities, and operating
   within the IP routing paradigm.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem Definition  . . . . . . . . . . . . . . . . . . . . .   3
   3.  SRv6 MUP and the 5G/Beyond 5G use cases . . . . . . . . . . .   3
     3.1.  Network Slicing . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Edge Computing  . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  URLLC (Ultra-Reliable Low-Latency Communication)
           support . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Co-existence and Incremental Deployability  . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The existing mobile user plane is currently defined as an overlay
   tunnel session to a mobile anchor point (UPF: User Plane Function in
   5G context).

   While this approach may be suited for use cases requiring frequent
   mobile handover and functionality tied to session initiation/
   termination, it proves challenging to cost-effectively and scalably
   address the high traffic volumes of the 5G/Beyond 5G era and the
   increasingly distributed data and computing demands in the future.

   The requirements for wireless systems are becoming more diverse, and
   there are cases , such as some IoT and FWA (Fixed Wireless Access)
   systems, where the frequent mobile handover is not necessarily
   mandatory.

   This document describes the solution approach and its architectural
   benefits of transforming mobile session information into routing
   information, leveraging segment routing capabilities, and operating
   within the IP routing paradigm.

   And this document clarifies the motivation for the MUP initiatives :
   [RFC9433][I-D.mhkk-dmm-mup-architecture]

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2.  Problem Definition

   The current tunnel session based mobile user plane has the following
   limitations and is getting hard to support new application
   requirements.

   *  Less suited for any-to-any communication

   *  Less suited for edge/distributed computing

   *  Less suited for fixed and mobile convergence (FMC) / wireless-
      wireline convergence (WWC)

   *  Limited control of the underlay path

   Mobile session information is a function of M,N (GTP-U session start
   point and end point), whereas routing information is a function of N
   (destination).  Therefore, for any-to-any communications, session
   based paradigm yields O(N^2), whereas IP routing paradigm yields
   O(N).

   Edge/distributed computing can be seen as a subset of any-to-any
   communication.  IP Routing paradigm naturally supports ubiquitous
   computing.

   As for FMC/WWC, there is currently a coordinated standardization
   effort between 3GPP WWC [TS.23316] and BBF [BBF407].  However, the
   idea is to anchor even wireline traffic in the mobile packet core,
   which compromises simplicity and scalability.

   In addition, the anchor point that terminates tunnel sessions becomes
   a scaling bottleneck.

   The IP routing paradigm naturally removes these tunnel session based
   restrictions.  Segment Routing enables fast protection, policy,
   multi-tenancy, and provide reliability and SLA differentiation.

3.  SRv6 MUP and the 5G/Beyond 5G use cases

   This section describes the advantages of applying the SRv6 Mobile
   User Plane approach for 5G/Beyond 5G use cases.  These advantage
   comes from the fact that it transforms mobile session information
   into routing information, leverages Segment Routing, and operates
   within the IP Routing Paradigm.  Another advantage, not mentioned
   here, is the ability to minimize overhead through SRv6 SID
   Compression.

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3.1.  Network Slicing

   Network slicing enables network segmentation, isolation, and SLA
   differentiation such as latency and availability.  End-to-end slicing
   will be achieved by mapping and coordinating IP network slicing, RAN
   and mobile packet core slicing.

   But existing mobile user plane which is overlay tunnel does not have
   underlying IP network awareness, which could lead to the inability in
   meeting SLAs.  Removing the tunnel and treating it with a IP routing
   paradigm simplifies the problem.

   Segment Routing has a comprehensive set of slice engineering
   technologies.  How to build network slicing using the Segment Routing
   technology is described in [I-D.ali-teas-spring-ns-building-blocks].

   Moreover, the stateless slice identifier encoding
   [I-D.filsfils-spring-srv6-stateless-slice-id] can be applicable to
   enable per-slice forwarding policy using the IPv6 header.

3.2.  Edge Computing

   Edge computing, where the computing workloads and datastores are
   placed closer to users, is recognized as one of the key pillars to
   meet demanding requirements of 5G/Beyond 5G era, with regard to low
   latency, bandwidth efficiency, data locality and privacy.

   Edge computing is more important than ever.  This is because no
   matter how much New Radio improves access speeds, it won't improve
   throughput, latency and user experiences because they are largely
   bound to end-to-end round trip delay.

   Even with existing mobile architectures, it is possible to place UPFs
   in a multi-tier, or to distribute UPFs, to achieve Edge Computing.
   [TS.23548] and [ETSI-MEC] describes how to properly select the UPF of
   adequate proximity.  However, complicated and signaling-heavy
   mechanisms are required to branch traffic or properly use different
   UPFs.  Also, if the UPF is distributed, seamless handover has to be
   compromised.

   When it comes to IP routing paradigum, ubiquitous computing is
   innately supported.

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3.3.  URLLC (Ultra-Reliable Low-Latency Communication) support

   3GPP [TR.23725] investigates the key issues for meeting the URLLC
   requirements on latency, jitter and reliability in the 5G System.
   The solutions provided in the document are focused at improving the
   overlay protocol (GTP-U) and limits to provide a few hints into how
   to map such tight-SLA into the transport network.  These hints are
   based on static configuration or static mapping for steering the
   overlay packet into the right transport SLA.  Such solutions do not
   scale and hinder network economics.

   Another issue that deserves special mention is the ultra-reliability
   issue.  In order to support ultra-reliability with the tunnel session
   paradigm, redundant user planes paths based on dual connectivity has
   been proposed.  The proposal has two main options.

   *  Dual Connectivity based end-to-end Redundant User Plane Path

   *  Support of redundant transmission on N3/N9 interfaces

   In the case of the former, UE and hosts have RHF(Redundancy Handling
   Function).  In sending, RFH is to replicate the traffic onto two
   GTP-U tunnels, and in receiving, RHF is to merge the traffic.

   In the case of the latter, traffic are to be replicated and merged
   with the same sequence for specific QoS flow, which requires further
   enhancements.

   And in either cases, the bigger problem is the lack of a reliable way
   for the redundant sessions to get through the disjoint path: even
   with the redundant sessions, if it ends up using the same
   infrastructure at some points, the redundancy is meaningless.

   These issues can be solved more simply without GTP-U tunnel.

   In addition, Segment routing has some advantages for URLLC traffic.
   First, traffic can be mapped to a disjoint path or low latency path
   as needed.  Second, Segment routing provides an automated reliability
   protection mechanism known as TI-LFA, which is a sub-50ms FRR
   mechanism that provides protection regardless of the topology through
   the optimal backup path.  It can be provisioned slice-aware.

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4.  Co-existence and Incremental Deployability

   Mobile networks are composed of radio, mobile packet core, and IP
   networks (access and backbone), with separate standard organizations
   and communities.  Therefore, in the steady state, it is difficult to
   innovate to a new architecture and requires coexistence and
   incremental deployment.

   [RFC9433] defines the user plane convergence between GTP-U and SRv6,
   so that it can co-exist with the existing user plane as needed.

   [I-D.mhkk-dmm-mup-architecture] defines the MUP architecture for
   Distributed Mobility Management, which can be plugged into the
   existing mobile service architecture.  In the architecture, mobile
   session information is transformed to routing information, and
   operated in L3VPN scheme.

5.  Security Considerations

   The deployment of this architecture is targeted in an administrative
   domain, and the functionality is domain specific.

6.  IANA Considerations

   This memo includes no request to IANA.

7.  References

7.1.  Normative References

   [RFC9433]  Matsushima, S., Ed., Filsfils, C., Kohno, M., Camarillo,
              P., Ed., and D. Voyer, "Segment Routing over IPv6 for the
              Mobile User Plane", RFC 9433, DOI 10.17487/RFC9433, July
              2023, <https://www.rfc-editor.org/rfc/rfc9433>.

7.2.  Informative References

   [BBF407]   BBF, "5G Wireless Wireline Convergence Architecture", BBF
              TR-407 Issue:1, August 2020.

   [ETSI-MEC] ETSI, "MEC in 5G Networks", ETSI White Paper No.28, June
              2018.

   [I-D.ali-teas-spring-ns-building-blocks]
              Ali, Z., Filsfils, C., Camarillo, P., Voyer, D.,
              Matsushima, S., Rokui, R., Dhamija, and P. Maheshwari,
              "Building blocks for Network Slice Realization in Segment
              Routing Network", Work in Progress, Internet-Draft, draft-

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              ali-teas-spring-ns-building-blocks-03, 7 September 2022,
              <https://datatracker.ietf.org/doc/html/draft-ali-teas-
              spring-ns-building-blocks-03>.

   [I-D.filsfils-spring-srv6-stateless-slice-id]
              Filsfils, C., Clad, F., Camarillo, P., Raza, S. K., Voyer,
              D., and R. Rokui, "Stateless and Scalable Network Slice
              Identification for SRv6", Work in Progress, Internet-
              Draft, draft-filsfils-spring-srv6-stateless-slice-id-10,
              22 July 2024, <https://datatracker.ietf.org/doc/html/
              draft-filsfils-spring-srv6-stateless-slice-id-10>.

   [I-D.mhkk-dmm-mup-architecture]
              Matsushima, S., Horiba, K., Kawakami, Y., Murakami, T.,
              Patel, K., and J. Horn, "Mobile User Plane Architecture
              for Distributed Mobility Management", Work in Progress,
              Internet-Draft, draft-mhkk-dmm-mup-architecture-02, 2
              March 2025, <https://datatracker.ietf.org/doc/html/draft-
              mhkk-dmm-mup-architecture-02>.

   [TR.23725] 3GPP, "Study on enhancement of Ultra-Reliable Low-Latency
              Communication (URLLC) support in the 5G Core network
              (5GC)", 3GPP TR 23.725 16.2.0, June 2019.

   [TS.23316] 3GPP, "Wireless and wireline convergence access support
              for the 5G System (5GS)", 3GPP TS 23.316 16.7.0, September
              2021.

   [TS.23548] 3GPP, "5G system Enhacements for Edge Computing", 3GPP TS
              23.548 17.0.0, September 2021.

Acknowledgements

   Authors would like to thank Satoru Matsushima, Shunsuke Homma, Yuji
   Tochio and Jeffrey Zhang, for their insights and comments.

Contributors

   Francois Clad
   Cisco Systems, Inc.
   France
   Email: fclad.ietf@gmail.com

   Pablo Camarillo Garvia
   Cisco Systems, Inc.
   Spain
   Email: pcamaril@cisco.com

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   Zafar Ali
   Cisco Systems, Inc.
   United States of America
   Email: zali@cisco.com

Authors' Addresses

   Teppei Kamata
   Cisco Systems, Inc.
   Japan
   Email: tkamata@cisco.com

   Jakub Horn
   Cisco Systems, Inc.
   Czech Republic
   Email: jakuhorn@cisco.com

   Luay Jalil
   Verizon
   United States of America
   Email: luay.jalil@verizon.com

   Weiqiang Cheng
   China Mobile
   China
   Email: chengweiqiang@chinamobile.com

   Miya Kohno
   Keio University
   Japan
   Email: miya_kohno@keio.jp

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