[Search] [txt|pdf|bibtex] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04                                                
DMM Working Group                                               M. Kohno
Internet-Draft                                                   F. Clad
Intended status: Informational                              P. Camarillo
Expires: November 7, 2021                                         Z. Ali
                                                     Cisco Systems, Inc.
                                                             May 6, 2021


           Architecture Discussion on SRv6 Mobile User plane
                    draft-kohno-dmm-srv6mob-arch-04

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 November 7, 2021.

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 November 7, 2021                [Page 1]


Internet-Draft                SRv6mob-arch                      May 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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  SRv6 mobile user plane and the 5G use cases . . . . . . . . .   4
     5.1.  Network Slicing . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Edge Computing  . . . . . . . . . . . . . . . . . . . . .   5
     5.3.  URLLC (Ultra-Reliable Low-Latency Communication) support    6
   6.  Control Plane Considerations  . . . . . . . . . . . . . . . .   7
   7.  Incremental Deployment  . . . . . . . . . . . . . . . . . . .   8
   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, 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 November 7, 2021                [Page 2]


Internet-Draft                SRv6mob-arch                      May 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 can be eliminated depending on the situations (e.g.  PPPoE
   -> IPoE, VXLAN/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 [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.

   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.



Kohno, et al.           Expires November 7, 2021                [Page 3]


Internet-Draft                SRv6mob-arch                      May 2021


4.  Terminology

   The terminology used in this document leverages and conforms to
   [I-D.ietf-dmm-srv6-mobile-uplane].

                                  +-----+
                                  | 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.




Kohno, et al.           Expires November 7, 2021                [Page 4]


Internet-Draft                SRv6mob-arch                      May 2021


5.1.  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.

5.2.  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-
   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.





Kohno, et al.           Expires November 7, 2021                [Page 5]


Internet-Draft                SRv6mob-arch                      May 2021


   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.

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




Kohno, et al.           Expires November 7, 2021                [Page 6]


Internet-Draft                SRv6mob-arch                      May 2021


   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.

6.  Control Plane Considerations

   This draft focuses on commonalization of data plane, and control
   plane is out of scope.  Having said that, IGP and BGP extension for
   SRv6 can be used as the control plane as they are.

   As for the mobility management, Loc/ID mapping protocol or the
   exisitng 3GPP control plane can still be used with slight
   modification, as stated in [I-D.ietf-dmm-srv6-mobile-uplane].




Kohno, et al.           Expires November 7, 2021                [Page 7]


Internet-Draft                SRv6mob-arch                      May 2021


   And even pure ID based anchorless protocol such as hICN
   [I-D.auge-dmm-hicn-mobility] can be used for mobility management as
   well.

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.  Various co-
   existence scenario are examined and described in
   [I-D.ietf-dmm-srv6-mobile-uplane].

   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, Shunsuke Homma and
   Yuji Tochio, 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., Garvia, P. C.,
              Voyer, D., and C. E. Perkins, "Segment Routing IPv6 for
              Mobile User Plane", draft-ietf-dmm-srv6-mobile-uplane-11
              (work in progress), April 2021.




Kohno, et al.           Expires November 7, 2021                [Page 8]


Internet-Draft                SRv6mob-arch                      May 2021


   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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, <https://www.rfc-editor.org/info/rfc8402>.

   [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,
              <https://www.rfc-editor.org/info/rfc8754>.

   [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,
              <https://www.rfc-editor.org/info/rfc8986>.

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-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.







Kohno, et al.           Expires November 7, 2021                [Page 9]


Internet-Draft                SRv6mob-arch                      May 2021


   [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-interop]
              Filsfils, C., Clad, F., Garvia, P. C., 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.

   [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-02
              (work in progress), January 2021.

   [I-D.guichard-spring-srv6-simplified-firewall]
              Guichard, J. N., Filsfils, C., Bernier, 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. E. Perkins, "Protocol for Forwarding
              Policy Configuration (FPC) in DMM", draft-ietf-dmm-fpc-
              cpdp-14 (work in progress), September 2020.

   [RFC5213]  Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
              Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
              RFC 5213, DOI 10.17487/RFC5213, August 2008,
              <https://www.rfc-editor.org/info/rfc5213>.

   [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.



Kohno, et al.           Expires November 7, 2021               [Page 10]


Internet-Draft                SRv6mob-arch                      May 2021


   [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


   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 November 7, 2021               [Page 11]