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 Verizon 15 February 2024 Architecture Discussion on SRv6 Mobile User plane draft-ietf-dmm-srv6mob-arch-00 Abstract 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 working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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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 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. Kohno, et al. Expires 18 August 2024 [Page 2] Internet-Draft SRv6mob-arch February 2024 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 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 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. Kohno, et al. Expires 18 August 2024 [Page 3] Internet-Draft SRv6mob-arch February 2024 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. Kohno, et al. Expires 18 August 2024 [Page 4] Internet-Draft SRv6mob-arch February 2024 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. 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. Kohno, et al. Expires 18 August 2024 [Page 5] Internet-Draft SRv6mob-arch February 2024 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, . [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, . Kohno, et al. Expires 18 August 2024 [Page 6] Internet-Draft SRv6mob-arch February 2024 [I-D.ali-teas-spring-ns-building-blocks] 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, . [I-D.filsfils-spring-srv6-stateless-slice-id] 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 2018. [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 2021. [BBF407] BBF, "5G Wireless Wireline Convergence Architecture", BBF TR-407 Issue:1, August 2020. Authors' Addresses Miya Kohno Cisco Systems, Inc. Japan Email: mkohno@cisco.com Kohno, et al. Expires 18 August 2024 [Page 7] Internet-Draft SRv6mob-arch February 2024 Francois Clad Cisco Systems, Inc. France Email: fclad@cisco.com Pablo Camarillo Garvia Cisco Systems, Inc. Spain Email: pcamaril@cisco.com Zafar Ali Cisco Systems, Inc. Canada Email: zali@cisco.com Luay Jalil Verizon United States Email: luay.jalil@verizon.com Kohno, et al. Expires 18 August 2024 [Page 8]