DMM Working Group T. Kamata
Internet-Draft F. Clad
Intended status: Informational P. Camarillo
Expires: 2 September 2025 Z. Ali
Cisco Systems, Inc.
L. Jalil
Verizon
W. Cheng
China Mobile
M. Kohno
Keio University
1 March 2025
Architecture Discussion on SRv6 Mobile User plane
draft-ietf-dmm-srv6mob-arch-01
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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Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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.
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And this document clarifies the motivation for the MUP initiatives :
[RFC9433][I-D.mhkk-dmm-srv6mup-architecture]
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
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Compression.
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-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.
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
[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-
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>.
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[I-D.mhkk-dmm-srv6mup-architecture]
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,
<https://datatracker.ietf.org/doc/html/draft-mhkk-dmm-
srv6mup-architecture-06>.
[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.
[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.
Authors' Addresses
Teppei Kamata
Cisco Systems, Inc.
Japan
Email: tkamata@cisco.com
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Francois Clad
Cisco Systems, Inc.
France
Email: fclad.ietf@gmail.com
Pablo Camarillo Garvia
Cisco Systems, Inc.
Spain
Email: pcamaril@cisco.com
Zafar Ali
Cisco Systems, Inc.
United States of America
Email: zali@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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