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Architecture Discussion on SRv6 Mobile User plane

Document Type Active Internet-Draft (individual)
Authors Miya Kohno , Francois Clad , Pablo Camarillo , Zafar Ali
Last updated 2023-03-12
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DMM Working Group                                               M. Kohno
Internet-Draft                                                   F. Clad
Intended status: Informational                              P. Camarillo
Expires: 10 September 2023                                        Z. Ali
                                                     Cisco Systems, Inc.
                                                            9 March 2023

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

   This Internet-Draft will expire on 10 September 2023.

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Table of Contents

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

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 convenient from the standpoint of 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 of the future.

   In addition, the requirements for wireless systems, such as IoT and
   FWA (Fixed Wireless Access) applications, are becoming more diverse,
   and there are cases where the conventional per-session per-usage
   charging is not necessarily applicable.

   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
   a routing paradigm.

2.  Problem Definition

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

   *  Non-optimal for any-to-any communication
   *  Non-optimal for edge/distributed computing
   *  Non-optimal for fixed and mobile convergence (FMC)
   *  No control of the underlay path

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

   As for FMC, 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.

   The IP routing paradigm naturally eliminates these tunnel session
   based shortcomings.  Segment Routing enables fast protection, policy,
   slicing, etc. to 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.

   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 routing
   paradigm simplifies the problem.

   Segment Routing has a comprehensive set of slice engineering
   technologies.  How to build network slicing using the Segment Routing
   based technology is described in

   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, and data localty and privacy.

   Edge computing is more important than ever.  This is because no
   matter how much 5G improves access speeds, it won't improve end-to-
   end throughput because it's largely bound to round trip delay.

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   Even with existing mobile architectures, it is possible to place UPFs
   in a multi-tier, or to distribute UPFs, to achieve Edge Computing.
   However, complicated mechanisms are required to branch traffic or
   properly use different UPFs.  Also, seamless handover needs to be
   compromised when UPFs are distributed.

   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.

   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 Paths
   *  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.

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4.  Co-existence and Incremental Deployability

   The mobile domain is a compound domain that includes Radio Access,
   and it is difficult to implement a completely new architecture, so
   co-existence and incremental deployability is required.

   [I-D.ietf-dmm-srv6-mobile-uplane] defines the data plane convergence
   between GTP-U and SRv6 between GTP-U and SRv6, so that it can co-
   exist with the current mobile architecture as needed.

   Further, [I-D.mhkk-dmm-srv6mup-architecture] defines the MUP
   architecture for Distributed Mobility Management, which can be
   plugged to the existing mobile service architecture.

5.  Security Considerations

   The deployment of this architecture is targeted in a trusted domain.

6.  IANA Considerations


7.  Acknowledgements

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

8.  References

8.1.  Normative References

              Psenak, P., Hegde, S., Filsfils, C., and A. Gulko, "ISIS
              Segment Routing Flexible Algorithm", Work in Progress,
              Internet-Draft, draft-hegdeppsenak-isis-sr-flex-algo-02,
              16 February 2018, <

              Matsushima, S., Filsfils, C., Kohno, M., Camarillo, P.,
              and D. Voyer, "Segment Routing IPv6 for Mobile User
              Plane", Work in Progress, Internet-Draft, draft-ietf-dmm-
              srv6-mobile-uplane-24, 17 January 2023,

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

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,

8.2.  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

              Ali, Z., Filsfils, C., Camarillo, P., and D. Voyer,
              "Building blocks for Slicing in Segment Routing Network",
              Work in Progress, Internet-Draft, draft-ali-spring-
              network-slicing-building-blocks-04, 21 February 2021,

              Auge, J., Carofiglio, G., Muscariello, L., and M.
              Papalini, "Anchorless mobility through hICN", Work in
              Progress, Internet-Draft, draft-auge-dmm-hicn-mobility-04,
              7 July 2020, <

              Auge, J., Carofiglio, G., Muscariello, L., and M.
              Papalini, "Anchorless mobility management through hICN
              (hICN-AMM): Deployment options", Work in Progress,

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              Internet-Draft, draft-auge-dmm-hicn-mobility-deployment-
              options-04, 7 July 2020,

              Chunduri, U., Li, R., Bhaskaran, S., Kaippallimalil, J.,
              Tantsura, J., Contreras, L. M., and P. Muley, "Transport
              Network aware Mobility for 5G", Work in Progress,
              Internet-Draft, draft-clt-dmm-tn-aware-mobility-09, 12
              February 2021, <

              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-07,
              29 January 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, "Segment Routing IPv6 Mobile User
              Plane Architecture for Distributed Mobility Management",
              Work in Progress, Internet-Draft, draft-mhkk-dmm-srv6mup-
              architecture-04, 24 October 2022,

   [RFC5213]  Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
              Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
              RFC 5213, DOI 10.17487/RFC5213, August 2008,

   [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.

   [TR.29892] 3GPP, "Study on User Plane Protocol in 5GC", 3GPP TR
              29.892 16.1.0, April 2019.

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

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

   [TS.29244] 3GPP, "Interface between the Control Plane and the User
              Plane Nodes", 3GPP TS 29.244 15.0.0, December 2017.

   [TS.29281] 3GPP, "General Packet Radio System (GPRS) Tunnelling
              Protocol User Plane (GTPv1-U)", 3GPP TS 29.281 15.1.0,
              December 2017.

Authors' Addresses

   Miya Kohno
   Cisco Systems, Inc.

   Francois Clad
   Cisco Systems, Inc.

   Pablo Camarillo Garvia
   Cisco Systems, Inc.

   Zafar Ali
   Cisco Systems, Inc.

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