DMM Working Group M. Kohno Internet-Draft F. Clad Intended status: Informational P. Camarillo Expires: May 6, 2021 Z. Ali Cisco Systems, Inc. November 2, 2020 Architecture Discussion on SRv6 Mobile User plane draft-kohno-dmm-srv6mob-arch-03 Abstract This document discusses a 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 6, 2021. Copyright Notice Copyright (c) 2020 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 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. Kohno, et al. Expires May 6, 2021 [Page 1] Internet-Draft SRv6mob-arch November 2020 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Problem Definition . . . . . . . . . . . . . . . . . . . . . 2 3. Common data plane across domains and across overlay/underlay 3 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 5. SRv6 mobile user plane and the 5G use cases . . . . . . . . . 4 5.1. Network Slicing . . . . . . . . . . . . . . . . . . . . . 4 5.2. Edge Computing . . . . . . . . . . . . . . . . . . . . . 5 5.3. URLLC (Ultra-Reliable Low-Latency Communication) support 6 6. Control Plane Considerations . . . . . . . . . . . . . . . . 7 7. Incremental Deployment . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 11.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 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, it will not be able to efficiently meet the diverse SLA requirements of the 5G era. Also, it will not be able to meet the demands of new mobile first and/or data intensive applications. This document discusses a solution approach and its architectural benefits of common data plane across domains (e.g., mobile including UE, IP transport, data center, applications) and across overlay/ underlay. This approach is in a sense contrary to proposals that the underlying transport can be anything (L2, IPv4, IPv6, MPLS, SR, SRv6). But it is an approach to make the network as flat as possible, making it suitable for the distributed mobile deployment model. 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 lack a way to map to the underlay Kohno, et al. Expires May 6, 2021 [Page 2] Internet-Draft SRv6mob-arch November 2020 o Non-optimal for edge/distributed computing o Lack a way for application developers to manipulate In addition, the centralized tunnel terminating gateway becomes a scaling bottleneck and a single point of failure For IP and data center networking, tunnel sessions can be eliminated when necessary and if possible (e.g. PPPoE -> IPoE, VXLAN/GENEVE/NSH -> SRv6), but such an architectural change used to be difficult for mobile domain. 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 [I-D.ietf-spring-srv6-network-programming] 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. Data plane commonality offers significant advantage regarding function, scaling, and cost. In particular, the benefits of the 5G era are shown in Section 5. Note that the interaction with underlay infrastructure is not a mandatory in the data plane commonality. It just gives a design option to interact with the underlay and optimize it, and it is totally fine to keep ovelray underlay-agnostic. 4. Terminology The terminology used in this document leverages and conforms to [I-D.ietf-dmm-srv6-mobile-uplane]. Kohno, et al. Expires May 6, 2021 [Page 3] Internet-Draft SRv6mob-arch November 2020 +-----+ | AMF | +-----+ / | [N11] [N2] / +-----+ +------/ | SMF | / +-----+ / / \ / / \ [N4] / / \ ________ / / \ / \ +--+ +-----+ [N3] +------+ [N9] +------+ [N6] / \ |UE|------| gNB |------| UPF1 |--------| UPF2 |--------- \ DN / +--+ +-----+ TN +------+ TN +------+ \________/ | _______ / \ / Local \ \ DN / \_______/ Figure 1: Reference Architecture - UE : User Equipment - gNB : gNodeB - UPF : User Plane Function - SMF : Session Management Function - AMF : Access and Mobility Management Function - 3GPP data plane entities : 3GPP entities responsible for data plane forwarding, i.e. gNB and UPF - TN : Transport Network - IP network where 3GPP data plane entities connected - DN : Data Network e.g. operator services, Internet access - CUPS : Control Plane and User Plane Separation - VNF : Virtual Network Function - CNF : Cloud native Network Function 5. 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. 5.1. Network Slicing Network slicing enables network segmentation, isolation, and SLA differentiation in terms of latency and availability. End-to-end Kohno, et al. Expires May 6, 2021 [Page 4] Internet-Draft SRv6mob-arch November 2020 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 efficiently 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. And In some deployment scenarios, it may be better to have a transport network PE present. For such a case, 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. 5.2. Edge Computing Edge computing, where the computing workload is placed closer to users, is recognized as one of the key pillars to meet 5G's demanding key performance indicators (KPIs), especially with regard to low latency and bandwidth efficiency. The computing workload includes network services, security, analytics, content cache and various applications. (UPF 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- end throughput because it's largely bound to round trip delay. 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. Kohno, et al. Expires May 6, 2021 [Page 5] Internet-Draft SRv6mob-arch November 2020 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. 5.3. 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. 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 Kohno, et al. Expires May 6, 2021 [Page 6] Internet-Draft SRv6mob-arch November 2020 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. SRv6 mobile user plane has some advantages for URLLC traffic. First, it can be used to enforce a low-latency path in the network by means of 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. 6. Control Plane Considerations This draft focuses on commonalization of data plane, and control plane is out of scope for now. Having said that, IGP and BGP extension for SRv6 can be used as the control plane as they are. As for the mobility management, BGP based Loc/ID mapping would be straightforward to implement. Or even pure ID based anchorless protocol such as hICN [I-D.auge-dmm-hicn-mobility] can be used. The co-existence with the 3GPP control plane is for further study. 7. Incremental Deployment Although it may seem difficult to migrate from the current mobile architecture, the conversion between GTP-U and SRv6 has been defined and can co-exist with the current mobile architecture as needed. Since the conversion is done completely statelessly (i.e., all necessary information is retained in the packet), there will not be a scaling bottleneck or a single point of failure. Kohno, et al. Expires May 6, 2021 [Page 7] Internet-Draft SRv6mob-arch November 2020 With regard to the architectural migration, the insertion with no modification to the existing 3GPP architecture is considered first, and then the tighter integration of data plane is to be achieved. as described in [I-D.auge-dmm-hicn-mobility-deployment-options]. 8. Security Considerations TBD 9. IANA Considerations NA 10. Acknowledgements Authors would like to thank Satoru Matsushima and Shunsuke Homma for their insights and comments. 11. References 11.1. 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., Camarillo, P., Voyer, D., and C. Perkins, "Segment Routing IPv6 for Mobile User Plane", draft-ietf-dmm-srv6-mobile-uplane-09 (work in progress), July 2020. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", draft-ietf-spring-segment-routing-15 (work in progress), January 2018. [I-D.ietf-spring-srv6-network-programming] Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "SRv6 Network Programming", draft-ietf-spring-srv6-network-programming-24 (work in progress), October 2020. Kohno, et al. Expires May 6, 2021 [Page 8] Internet-Draft SRv6mob-arch November 2020 [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, . 11.2. Informative References [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-02 (work in progress), November 2019. [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., and P. Muley, "Transport Network aware Mobility for 5G", draft-clt-dmm-tn-aware- mobility-07 (work in progress), September 2020. [I-D.filsfils-spring-srv6-interop] Filsfils, C., Clad, F., Camarillo, P., Abdelsalam, A., Salsano, S., Bonaventure, O., Horn, J., and J. Liste, "SRv6 interoperability report", draft-filsfils-spring- srv6-interop-02 (work in progress), March 2019. Kohno, et al. Expires May 6, 2021 [Page 9] Internet-Draft SRv6mob-arch November 2020 [I-D.filsfils-spring-srv6-stateless-slice-id] Filsfils, C., Clad, F., Camarillo, P., and K. Raza, "Stateless and Scalable Network Slice Identification for SRv6", draft-filsfils-spring-srv6-stateless-slice-id-01 (work in progress), July 2020. [I-D.guichard-spring-srv6-simplified-firewall] Guichard, J., Filsfils, C., daniel.bernier@bell.ca, d., Li, Z., Clad, F., Camarillo, P., and A. Abdelsalam, "Simplifying Firewall Rules with Network Programming and SRH Metadata", draft-guichard-spring-srv6-simplified- firewall-02 (work in progress), April 2020. [I-D.ietf-dmm-fpc-cpdp] Matsushima, S., Bertz, L., Liebsch, M., Gundavelli, S., Moses, D., and C. Perkins, "Protocol for Forwarding Policy Configuration (FPC) in DMM", draft-ietf-dmm-fpc-cpdp-14 (work in progress), September 2020. [I-D.rokui-5g-transport-slice] Rokui, R., Homma, S., Lopez, D., Foy, X., Contreras, L., Ordonez-Lucena, J., Martinez-Julia, P., Boucadair, M., Eardley, P., Makhijani, K., and H. Flinck, "5G Transport Slice Connectivity Interface", draft-rokui-5g-transport- slice-00 (work in progress), July 2019. [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.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. Kohno, et al. Expires May 6, 2021 [Page 10] Internet-Draft SRv6mob-arch November 2020 [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 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 6, 2021 [Page 11]