DMM Working Group M. Kohno Internet-Draft F. Clad Intended status: Informational P. Camarillo Expires: May 12, 2022 Z. Ali Cisco Systems, Inc. November 8, 2021 Architecture Discussion on SRv6 Mobile User plane draft-kohno-dmm-srv6mob-arch-05 Abstract SRv6 mobile user plane is standardized in IETF. It accomplishes the mobile user-plane functions in a simple, flexible and scalable manner, by utilizing the network programming nature of SRv6. It leverages common native IPv6 data plane and creates interoperable overlays with underlay optimization. This document discusses the solution approach and its architectural benefits of common data plane across domains and across overlay/ underlay. 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on May 12, 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of Kohno, et al. Expires May 12, 2022 [Page 1] Internet-Draft SRv6mob-arch November 2021 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Problem Definition . . . . . . . . . . . . . . . . . . . . . 3 3. Common data plane across domains and across overlay/underlay 3 4. Control Plane Considerations . . . . . . . . . . . . . . . . 4 5. Incremental Deployability . . . . . . . . . . . . . . . . . . 4 6. SRv6 mobile user plane and the 5G use cases . . . . . . . . . 5 6.1. Network Slicing . . . . . . . . . . . . . . . . . . . . . 5 6.2. Edge Computing . . . . . . . . . . . . . . . . . . . . . 5 6.3. URLLC (Ultra-Reliable Low-Latency Communication) support 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 10.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction Mobile architectures have evolved individually, and the user plane, GTP-U, has been defined as an overlay tunnel that is agnostic to the IP infrastructure. However, the system requirements are changing as digitalization goes into full swing. The continued use of GTP-U as a user plane protocol will lock-in to the existing architectural structure and hinder the innovation. GTP-U will not be able to meet the diverse SLA requirements of the 5G era and beyond with efficiency and scalability. Also it will not be able to meet the demands of new mobile-first data intensive applications, which will be more dynamically distributed. SRv6 mobile user plane [I-D.ietf-dmm-srv6-mobile-uplane] is standardized in IETF. It accomplishes the mobile user-plane functions in a simple, flexible and scalable manner, by utilizing the network programming nature of SRv6. It leverages common native IPv6 data plane and creates interoperable overlays with underlay optimization. Kohno, et al. Expires May 12, 2022 [Page 2] Internet-Draft SRv6mob-arch November 2021 This document discusses the solution approach and its architectural benefits of common data plane across domains (e.g., mobile domain, IP infrastructure, data center, applications) and across overlay/ underlay. 2. Problem Definition The current mobile user plane, GTP-U, defined as an overlay tunnel that is agnostic to the IP infrastructure, has the following limitations that prevent it from supporting new application demands. o Non-optimal for any-to-any communication o No control of the underlay path o Non-optimal for edge/distributed computing o Non-optimal for fixed and mobile path convergence o Lack a way for application/service developers to manipulate and interact In addition, the centralized tunnel terminating gateway becomes a scaling bottleneck and a single point of failure For residential broadband IP and data center networking, tunnel sessions could be eliminated (e.g. PPPoE -> IPoE, VXLAN/NSH -> SRv6). This indicates that a tunnel session is not necessarily absolute. But such a thing was unlikely to happen in the mobile domain. 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. 3. Common data plane across domains and across overlay/underlay [I-D.ietf-dmm-srv6-mobile-uplane] defines SRv6 mobile user plane as an alternative or co-existing solution to GTP-U. Since SRv6 is a native IPv6 data plane, it can be a common data plane regardless of the domain. SRv6 Network Programming [RFC8986] enables the creation of overlays with underlay optimization. In addition, SRv6 can be operated by application developers because of its implementation in the computing stack, e.g. VPP, Linux Kernel, smart NIC, and cloud native platform such as Network Service Mesh. Kohno, et al. Expires May 12, 2022 [Page 3] Internet-Draft SRv6mob-arch November 2021 Data plane commonality offers significant advantage regarding function, scaling, and cost. In particular, the benefits of the 5G era are shown in Section 6. Note that the interaction with underlay infrastructure is not a mandatory in the data plane commonality. It just gives a design choice to interact with the underlay and optimize it, and it is totally fine to keep ovelray underlay-agnostic, which will allow the coexistence of different capability of nodes. 4. Control Plane Considerations This document focuses on the commonalization of data plane, and the control plane is out of scope. The actual system characteristics such as scaling and functionality depend heavily on the control plane, though. The potential of the SRv6 mobile user plane is huge, in the sense that it can realize various functions of mobile management using SRv6 Network Programming. Protocols such as GTP-C, PMIPv6, BGP, LISP, ILNP, hICN, or even others can be applied as a control plane to control mobility. For example, if hICN [I-D.auge-dmm-hicn-mobility] was used, anchorless mobility can be realised. 5. Incremental Deployability The mobile domain is a compound domain that includes Radio Access, and it is difficult to implement a completely new architecture, and incremental deployability is required. [I-D.ietf-dmm-srv6-mobile-uplane] defines the conversion between GTP-U and SRv6, so that it can co-exist with the current mobile architecture as needed. Since the conversion is done statelessly (i.e., all necessary information is retained in the packet), there will not be a scaling bottleneck or a single point of failure. Further, [I-D.mhkk-dmm-srv6mup-architecture] defines the SRv6 MUP architecture for Distributed Mobility Management, which can be plugged to the existing mobile service architecture. In this way, SRv6 Network Programmability allows for proper deployability. Kohno, et al. Expires May 12, 2022 [Page 4] Internet-Draft SRv6mob-arch November 2021 6. SRv6 mobile user plane and the 5G use cases This section describes the advantages of the common data plane and of applying SRv6 mobile user plane for 5G use cases. 6.1. 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. However, as pointed out in [I-D.clt-dmm-tn-aware-mobility], the 5G System as defined, does not have underlying IP network awareness, which could lead to the inability in meeting SLAs. Segment Routing has a comprehensive set of slice engineering technologies. How to build network slicing using the Segment Routing based technology is described in [I-D.ali-spring-network-slicing-building-blocks]. In the typical GTP-U over IP/MPLS/SR configuration, 3GPP data plane entity such as UPF is a CE to the transport networks PE. But if 3GPP they support SRv6 mobile user plane, they can directly participate in network slicing, and solves the following issues. o A certain Extra ID such as VLAN-ID is needed for segregating traffic and mapping it onto a designated slice. o PE and the PE-CE connection is a single point of failure, so some form of PE redundancy (using routing protocols, MC-LAG, etc.) is required. 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. 6.2. 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 privacy. The computing workload includes network services, security, data analytics, content cache and various applications. (UPF itself can also be viewed as a distributed network service function.) Edge computing is more important than ever. This is because no matter how much 5G improves access speeds, it won't improve end-to- Kohno, et al. Expires May 12, 2022 [Page 5] Internet-Draft SRv6mob-arch November 2021 end throughput because it's largely bound to round trip delay. It is also important from the viewpoint of "local production for local consumption" and privacy protection. However, the current MEC discussion [ETSI-MEC] focuses on how to properly select the UPF of adequate proximity, and not on how to interact with applications. SRv6 has an advantage in enabling edge computing for the following reasons. o Programmable and Flexible Traffic Steering : SRv6's flexible traffic steering capabilities and the network programming concept is suitable for flexible placement of computing workload. o Common data plane across domains : SRv6/IPv6 can be a common data plane regardless of the domains such as mobile including UE, IP transport, data center, applications. o Stateless Service Chaining : It does not require any per-flow state in network fabric. o Interaction with Applications : SRv6 can be implemented in the compute stack and can be manipulated by applications using socket API. Also, SRv6 can carry meta data, which can be used for interacting with applications. o Functionality without performance degradation : Various information can be exposed in IP header, but it does not degrade performance thanks to the longest match mechanism in the IP routing. Only who needs the information for granular processing are to lookup. It is even more beneficial if service functions/applications directly support SRv6. 6.3. 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. Some of the issues can be solved more simply without GTP-U tunnel. SRv6 mobile user plane can exposes session and QoS flow information in IP header as discussed in the previous section. This would make routing and forwarding path optimized for URLLC, much simpler than the case with GTP-U tunnel. Kohno, et al. Expires May 12, 2022 [Page 6] Internet-Draft SRv6mob-arch November 2021 Another issue that deserves special mention is the ultra-reliability issue. In 3GPP, in order to support ultra-reliability, redundant user planes paths based on dual connectivity has been proposed. The proposal has two main options. o Dual Connectivity based end-to-end Redundant User Plane Paths o 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, the 3GPP data plane entities are to replicate and merge the packets 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. SRv6 mobile user plane has some advantages for URLLC traffic. First, with SRv6, Traffic can be mapped to a disjoint path or low latency path as needed, by means of the scalable Traffic Engineering. Additionally, SRv6 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. With the case that dual live-live path is required, the problem is not only the complexity but that the replication point and the merging point would be the single point of failure. The SRv6 mobile user plane also has an advantage in this respect, because any endpoints or 3GPP data plane nodes themselves can be the replication/ merging point when they are SRv6 aware. Furthermore, SRv6 supports inband telemetry/time stamping for latency monitoring and control. 7. Security Considerations TBD Kohno, et al. Expires May 12, 2022 [Page 7] Internet-Draft SRv6mob-arch November 2021 8. IANA Considerations NA 9. Acknowledgements Authors would like to thank Satoru Matsushima, Shunsuke Homma,Yuji Tochio and Jeffrey Zhang, for their insights and comments. 10. References 10.1. Normative References [I-D.hegdeppsenak-isis-sr-flex-algo] Psenak, P., Hegde, S., Filsfils, C., and A. Gulko, "ISIS Segment Routing Flexible Algorithm", draft-hegdeppsenak- isis-sr-flex-algo-02 (work in progress), February 2018. [I-D.ietf-dmm-srv6-mobile-uplane] Matsushima, S., Filsfils, C., Kohno, M., Garvia, P. C., Voyer, D., and C. E. Perkins, "Segment Routing IPv6 for Mobile User Plane", draft-ietf-dmm-srv6-mobile-uplane-17 (work in progress), October 2021. [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, . Kohno, et al. Expires May 12, 2022 [Page 8] Internet-Draft SRv6mob-arch November 2021 10.2. 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-spring-network-slicing-building-blocks] Ali, Z., Filsfils, C., Camarillo, P., and D. Voyer, "Building blocks for Slicing in Segment Routing Network", draft-ali-spring-network-slicing-building-blocks-04 (work in progress), February 2021. [I-D.auge-dmm-hicn-mobility] Auge, J., Carofiglio, G., Muscariello, L., and M. Papalini, "Anchorless mobility through hICN", draft-auge- dmm-hicn-mobility-04 (work in progress), July 2020. [I-D.auge-dmm-hicn-mobility-deployment-options] Auge, J., Carofiglio, G., Muscariello, L., and M. Papalini, "Anchorless mobility management through hICN (hICN-AMM): Deployment options", draft-auge-dmm-hicn- mobility-deployment-options-04 (work in progress), July 2020. [I-D.clt-dmm-tn-aware-mobility] Chunduri, U., Li, R., Bhaskaran, S., Kaippallimalil, J., Tantsura, J., Contreras, L. M., and P. Muley, "Transport Network aware Mobility for 5G", draft-clt-dmm-tn-aware- mobility-09 (work in progress), February 2021. [I-D.filsfils-spring-srv6-stateless-slice-id] Filsfils, C., Clad, F., Camarillo, P., Raza, K., Voyer, D., and R. Rokui, "Stateless and Scalable Network Slice Identification for SRv6", draft-filsfils-spring-srv6- stateless-slice-id-04 (work in progress), July 2021. [I-D.mhkk-dmm-srv6mup-architecture] Matsushima, S., Horiba, K., Khan, A., Kawakami, Y., Murakami, T., Patel, K., Kohno, M., Kamata, T., and P. Camarillo, "Segment Routing IPv6 Mobile User Plane Architecture for Distributed Mobility Management", draft- mhkk-dmm-srv6mup-architecture-00 (work in progress), October 2021. Kohno, et al. Expires May 12, 2022 [Page 9] Internet-Draft SRv6mob-arch November 2021 [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 2021. [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. Japan Email: mkohno@cisco.com Francois Clad Cisco Systems, Inc. France Email: fclad@cisco.com Kohno, et al. Expires May 12, 2022 [Page 10] Internet-Draft SRv6mob-arch November 2021 Pablo Camarillo Garvia Cisco Systems, Inc. Spain Email: pcamaril@cisco.com Zafar Ali Cisco Systems, Inc. Canada Email: zali@cisco.com Kohno, et al. Expires May 12, 2022 [Page 11]