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Architecture Discussion on SRv6 Mobile User plane

Document Type Active Internet-Draft (dmm WG)
Authors Miya Kohno , Francois Clad , Pablo Camarillo , Zafar Ali , Luay Jalil
Last updated 2024-02-15
Replaces draft-kohno-dmm-srv6mob-arch
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DMM Working Group                                               M. Kohno
Internet-Draft                                                   F. Clad
Intended status: Informational                              P. Camarillo
Expires: 18 August 2024                                           Z. Ali
                                                     Cisco Systems, Inc.
                                                                L. Jalil
                                                        15 February 2024

           Architecture Discussion on SRv6 Mobile User plane


   This document discusses the solution approach and its architectural
   benefits of translating mobile session information into routing
   information, applying segment routing capabilities, and operating in
   the IP routing paradigm.

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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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 18 August 2024.

Copyright Notice

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

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (
   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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   provided without warranty as described in the Revised BSD License.

Table of Contents

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

1.  Introduction

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

   While this approach may be well suited for the use cases which
   require frequent mobile handover and per-session per-usage charging,
   it is difficult to cost-effectively and scalably address the high
   traffic volumes of the 5G/Beyond 5G era and more distributed data and
   computing demands in future.

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

   This document discusses the solution approach and its architectural
   benefits of translating mobile session information into routing
   information, applying segment routing capabilities, and operating in
   the IP routing paradigm.

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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

   *  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 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

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

   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 mobile user plane and the 5G use cases

   This section describes the advantages of applying SRv6 mobile user
   plane for 5G use cases.

3.1.  Network Slicing

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

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   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 5G's demanding requirements, 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 5G New Radio improves access speeds, it won't improve
   end-to-end throughput because it's largely bound to 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 to some extent.

   IP Routing paradigm simply supports ubiquitous computing.

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.

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   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

   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.

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-srv6mup-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.

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5.  Security Considerations

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

6.  IANA Considerations

   This memo includes no request to IANA.

7.  Acknowledgements

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

8.  Normative References

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

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

   [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, <>.

              Matsushima, S., Horiba, K., Khan, A., Kawakami, Y.,
              Murakami, T., Patel, K., Kohno, M., Kamata, T., Camarillo,
              P., Horn, J., Voyer, D., Zadok, S., Meilik, I., Agrawal,
              A., and K. Perumal, "Mobile User Plane Architecture using
              Segment Routing for Distributed Mobility Management", Work
              in Progress, Internet-Draft, draft-mhkk-dmm-srv6mup-
              architecture-06, 23 October 2023,

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              Ali, Z., Filsfils, C., Camarillo, P., Voyer, D.,
              Matsushima, S., Rokui, R., Dhamija, A., and P. Maheshwari,
              "Building blocks for Network Slice Realization in Segment
              Routing Network", Work in Progress, Internet-Draft, draft-
              ali-teas-spring-ns-building-blocks-03, 7 September 2022,

              Filsfils, C., Clad, F., Camarillo, P., Raza, S., 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-09,
              29 January 2024, <

9.  Informative References

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

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

   [TS.23558] 3GPP, "Architecture for enabling Edge applications", 3GPP
              TS 23.558 17.0.0, June 2021.

   [TS.23501] 3GPP, "System Architecture for the 5G System", 3GPP TS
              23.501 15.0.0, November 2017.

   [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

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

Authors' Addresses

   Miya Kohno
   Cisco Systems, Inc.

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   Francois Clad
   Cisco Systems, Inc.

   Pablo Camarillo Garvia
   Cisco Systems, Inc.

   Zafar Ali
   Cisco Systems, Inc.

   Luay Jalil
   United States

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