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Versions: 00 01 02 03                                                   
Internet Engineering Task Force                            S. Matsushima
Internet-Draft                                                 K. Horiba
Intended status: Standards Track                                 A. Khan
Expires: 28 April 2022                                       Y. Kawakami
                                                                SoftBank
                                                             T. Murakami
                                                                K. Patel
                                                             Arrcus, Inc
                                                                M. Kohno
                                                               T. Kamata
                                                            P. Camarillo
                                                     Cisco Systems, Inc.
                                                         25 October 2021


  Segment Routing IPv6 Mobile User Plane Architecture for Distributed
                          Mobility Management
                 draft-mhkk-dmm-srv6mup-architecture-00

Abstract

   This document defines the Segment Routing IPv6 Mobile User Plane
   (SRv6 MUP) architecture for Distributed Mobility Management.  The
   requirements for Distributed Mobility Management described in
   [RFC7333] can be satisfied by routing fashion.

   Mobile services are deployed over several parts of IP networks.  A
   Segment Routing over IPv6 (SRv6) network can accommodate all, or part
   of those networks thanks to the large address space of IPv6 and the
   network programming capability described in [RFC8986].

   Segment Routing IPv6 Mobile User Plane Architecture can incorporate
   existing session based mobile networks.  By leveraging SRv6 network
   programmability, mobile user plane can be integrated into the SRv6
   data plane.  In that routing paradigm, session information between
   the entities of the mobile user plane is turned to routing
   information.

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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   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 29 April 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 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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Architecture Overview . . . . . . . . . . . . . . . . . . . .   5
   4.  Mobile User Plane Segment . . . . . . . . . . . . . . . . . .   6
   5.  Distribution of Mobile User Plane Segment Information . . . .   7
     5.1.  MUP PE  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  MUP GW  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  MUP Controller  . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Illustration  . . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Mobile services require IP connectivity for communication between the
   entities of mobile service architecture.  To provide the IP
   connectivity, Segment Routing (SR) [RFC8402]can be a candidate
   solution.





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   In PMIPv6 [RFC5213], IP connectivity between LMA and MAG can be
   provided over SR networks, as well as LMA and Internet.  In 3GPP 5G
   [TS.23501], IP connectivity for N3 interface between gNodeB(es) and
   UPFs can also be provided by SR, as well as for N6 interface between
   UPFs and DNs (Data Network).

   These IP connectivities may be covered by multiple SR networks, or
   just one SR network, depending on the size of the deployment.  In the
   latter case, it is expected that the address space of the SR network
   should be large enough to cover a vast number of nodes, such as
   millions of base stations.  For this reason, use of IPv6 for the SR
   dataplane looks sufficiently suitable.

   SRv6 is an instantiation of SR over IPv6 dataplane in which a single
   network can accommodate all entities of mobile services thanks to the
   huge available address space and network programming capability
   described in [RFC8986].

   Meanwhile, SRv6 network programmability enhances SRv6 dataplane to be
   integrated with mobile user plane [I-D.ietf-dmm-srv6-mobile-uplane].
   It will make an entire SRv6 network support the user plane in a very
   efficient distributed routing fashion.

   On the other hand, the requirements for Distributed Mobility
   Management (DMM) described in [RFC7333] can be satisfied by session
   management based solutions.  [RFC8885] defines protocol extension to
   PMIPv6 for the DMM requirements.  3GPP 5G defines an architecture in
   which multiple session anchors can be added to one mobility session
   by the session management.

   As a reminder, the user plane related requirements in [RFC7333] are
   reproduced here:

   REQ1: Distributed mobility management
           IP mobility, network access solutions, and forwarding
           solutions provided by DMM MUST enable traffic to avoid
           traversing a single mobility anchor far from the optimal
           route.  It is noted that the requirement on distribution
           applies to the data plane only.

   REQ3: IPv6 deployment
           DMM solutions SHOULD target IPv6 as the primary deployment
           environment and SHOULD NOT be tailored specifically to
           support IPv4, particularly in situations where private IPv4
           addresses and/or NATs are used.






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   REQ4: Existing mobility protocols
           A DMM solution MUST first consider reusing and extending IETF
           standard protocols before specifying new protocols.

   REQ5: Coexistence with deployed networks/hosts and operability
   across different networks
           A DMM solution may require loose, tight, or no integration
           into existing mobility protocols and host IP stacks.
           Regardless of the integration level, DMM implementations MUST
           be able to coexist with existing network deployments, end
           hosts, and routers that may or may not implement existing
           mobility protocols.  Furthermore, a DMM solution SHOULD work
           across different networks, possibly operated as separate
           administrative domains, when the needed mobility management
           signaling, forwarding, and network access are allowed by the
           trust relationship between them.

   This document defines the Segment Routing IPv6 Mobile User Plane
   (SRv6 MUP) architecture for Distributed Mobility Management.  SRv6
   MUP is not a mobility management system itself, but the DMM
   requirements are supported by leveraging SRv6 network programmability
   to integrate mobile user plane into the SR data plane.

   In this routing paradigm, session information from a mobility
   management system will be transformed to routing information.  It
   means that mobile user plane specific nodes for the anchor or
   intermediate points are no longer required.  The user plane anchor
   and access agent functions can be supported by SR throughout an SR
   domain (REQ1), not to mention that SRv6 MUP will naturally be
   deployed over IPv6 networks (REQ3).

   SRv6 MUP architecture is independent from the mobility management
   system.  For the requirements (REQ4, 5), SRv6 MUP architecture is
   designed to be pluggable user plane part of existing mobile service
   architectures.  Those existing architectures are for example defined
   in [RFC5213], [TS.23501], or if any.

   The level of SRv6 MUP integration for mobile networks running based
   on the existing architecture will be varied and depending on the
   level of SRv6 awareness of the control and user plane entities.

   Specifying how to modify the existing architecture to integrate SRv6
   MUP is out of scope of this document.  What this document provides
   for the existing architecture is an interface for SRv6 MUP which the
   existing or future architectures can easily integrate.






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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Terminology

   MUP:    Mobile User Plane

   MUP Segment:  Representation of mobile user plane segment

   MUP PE:  Provider Edge node in a MUP network

   MUP GW:  Gateway node to interwork with another mobile user plane
           networks

   MUP Controller:  Controller node for a MUP network

   UE:     User Equipment, as per [TS.23501]

   MN:     Mobile Node, as per [RFC5213]

3.  Architecture Overview

   SRv6 MUP architecture defined in this document introduces a new
   segment type of the SR called "Mobile User Plane (MUP) segment" and
   new routing information called "Segment Discovery route" and "Session
   Transformed route", then 3 new network nodes; MUP PE, MUP GW and MUP
   Controller.  Figure 1 depicts the overview.

   To carry these new routing information, this architecture requires
   extending the existing routing protocols.  Any routing protocol can
   be used to carry this information but this document recommends using
   BGP.  Thus, this document describes extensions on BGP as an example.
















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                              *   Mobility   *
                               * Management *
                                *  System  *
                                 *........*
                                    |
                             Session Information
                                    |
                                    v
                            +----------------+
                          --| MUP Controller |--            ___________
                         /  +----------------+  \          /           \
     ___________        /         _______    +--------+   /             \
    /           \      /         /       \---| MUP PE |---\ MUP Segment /
   /             \  +--------+  /         \  +--------+    \___________/
   \ MUP Segment /--| MUP GW |--\ SRv6 NW /  +--------+     ___________
    \___________/   +--------+   \_______/---| MUP PE |----/           \
                                             +--------+   /             \
                                                          \ MUP Segment /
                                                           \___________/


                               Figure 1

4.  Mobile User Plane Segment

   This document defines one new segment type.  A Mobile User Plane
   (MUP) segment may represent a network segment consisting of a mobile
   service.  The MUP segment can be created by an SR node which provides
   connectivity for the mobile user plane.  The MUP segment SID can be
   any behavior defined in [RFC8986], [I-D.ietf-dmm-srv6-mobile-uplane],
   or any other extensions for further use cases.

   The behavior of the MUP segment will be chosen by the role of the
   representing mobile network segment.  For example, in case of an SR
   node interfaces to 5G user plane on the access side defined as "N3"
   in [TS.23501], the behavior of created segment SID will be
   "End.M.GTP4.E", or "End.M.GTP6.E".  In this case, the SR node may
   associate the SID to a N3 access network (N3RAN) routing instance.

   Another example here is the "N6" interface on the core data network
   side.  The behavior of the created segment SID will be "End.DT4",
   "End.DT6", or "End.DT2".  In this case the SR node may associate the
   SID to a N6 data network (N6DN) routing instance.








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5.  Distribution of Mobile User Plane Segment Information

   Distribution of MUP segment information can be done by advertising
   routing information with the MUP segment for mobile service.  This
   document defines two types of SR node, MUP PE and MUP GW, for
   distributing MUP segment information.

   A MUP Segment Discovery route is routing information, of which a MUP
   segment is associated with network reachability.  This document
   defines the basic network reachability types, Direct type
   reachability, and Interwork type reachability.  Other types of
   network reachability may be mobile service architecture specific.
   Define the architecture specific network reachability is out of scope
   of this document and it will be specified in another document.

5.1.  MUP PE

   A MUP PE accommodates a MUP segment to a routing instance for direct
   reachability.  The MUP PE advertises the MUP segment discovery route
   for the routing instance with the direct network reachability
   information and the corresponding MUP segment to the SR domain.

   For example in 3GPP 5G specific case, an MUP PE may connect to N6
   interface on a DN side, an MUP segment discovery route for the DN
   will be advertised with a N6DN reachability and corresponding SID
   from the MUP PE.

   The MUP PE keeps the received MUP segment discovery routes advertised
   from other MUP PEs in the RIB.  The MUP PE uses those received MUP
   segment discovery routes to resolve the nexthop of routes for UE, MN
   or any other IP prefixes.  If a MUP segment discovery route matches
   to a nexthop, the MUP PE updates the FIB entry for the route with the
   SID of the matched MUP segment discovery route.

5.2.  MUP GW

   A MUP GW interfaces an MUP segment with the user plane protocol for
   the existing mobile service architecture.  The MUP GW accommodates
   the MUP segment to a routing instance for the existing mobile service
   architecture.  The MUP GW advertises the corresponding MUP segment
   discovery route with the interwork type reachability to the SR
   domain.

   For example in 3GPP 5G specific case, an interwork reachability for
   N3 network accommodating RAN will be incorporated in an N3RAN segment
   discovery route associated with a RAN segment SID.





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   When a MUP GW receives a MUP segment discovery route with direct type
   reachability, the MUP GW creates an SR Policy
   [I-D.ietf-spring-segment-routing-policy] to the MUP segment with the
   associated BSID.  For example in 3GPP 5G specific case, the BSID
   behavior for the N6DN segment discovery route will be H.M.GTP4.D or
   H.M.GTP6.D.  The received SID in the N6DN segment discovery route
   will be the last SID of the created SR Policy.

   The MUP GW may keep the received MUP segment discovery routes
   advertised from other MUP GWs in the routing instance.  The IP
   prefixes for the received segments are imported into the routing
   instance table.  Thereby the MUP GW can provide network connectivity
   between the nodes that exist in the segments.

   The MUP GW may also accommodate another type of routing instance for
   the routes of UE, MN or any other IP prefixes.  In this case, the MUP
   GW creates an SR policy with the BSID for the routing instance table
   lookup.

6.  MUP Controller

   A MUP controller provides a northbound API.  A consumer of the API
   inputs session information for a UE or a MN from mobility management
   system.  The MUP controller transforms the received session
   information to routing information and will advertise the transformed
   route to the SR domain.

   The received session information is expected to include the UE or MN
   IP prefix(es), tunnel endpoint identifiers for both ends, and any
   other attributes for the mobile networks.  For example in a 3GPP 5G
   specific case, the tunnel endpoint identifier will be a pair of the
   F-TEIDs on both the N3 access side (RAN) and core side (UPF).

   SRv6 MUP architecture defines two types of session transformed route.

   First type route is that IP prefix(es) for a UE or MN may be encoded
   in a BGP MP-NLRI attribute with associated session information of the
   tunnel endpoint identifier on the access side.  The MUP controller
   advertises the UE or MN route to the SR domain.

   Second type route is that the tunnel endpoint identifier of the
   session on the core side may also be encoded in another BGP MP-NLRI
   attribute.  And the MUP controller also advertises this type of route
   with the BSID of SR Policy corresponding to the core MUP segment.







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   To ensure advertising the second type route, the MUP controller
   collects SR Policies for the segments advertised from MUP GWs in the
   SR domain.  The MUP controller maintains the collected SR Policies
   and manages them for the corresponding core segment.

   MUP PE and GW are expected to receive the routes advertised from the
   MUP controller.  A MUP PE imports a route for UE or MN into the
   corresponding Direct type routing instance.  A MUP GW imports a route
   for core side session tunnel endpoint identifier into the
   corresponding Interwork type routing instance.

7.  Illustration

   The illustration of SRv6 MUP architecture will be filled in next
   revisions.

8.  IANA Considerations

   This memo includes no request to IANA.

9.  Security Considerations

   TBD.

10.  References

10.1.  Normative References

   [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", Work in Progress, Internet-Draft,
              draft-ietf-dmm-srv6-mobile-uplane-17, 12 October 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-dmm-
              srv6-mobile-uplane-17>.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", Work in
              Progress, Internet-Draft, draft-ietf-spring-segment-
              routing-policy-13, 28 May 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              segment-routing-policy-13>.

   [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>.



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   [RFC7333]  Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J.
              Korhonen, "Requirements for Distributed Mobility
              Management", RFC 7333, DOI 10.17487/RFC7333, August 2014,
              <https://www.rfc-editor.org/info/rfc7333>.

   [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>.

   [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>.

10.2.  Informative References

   [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>.

   [RFC8885]  Bernardos, CJ., de la Oliva, A., Giust, F., Zúñiga, JC.,
              and A. Mourad, "Proxy Mobile IPv6 Extensions for
              Distributed Mobility Management", RFC 8885,
              DOI 10.17487/RFC8885, October 2020,
              <https://www.rfc-editor.org/info/rfc8885>.

   [TS.23501] 3GPP, "System architecture for the 5G System (5GS)", 3GPP
              TS 23.501 17.2.0, 24 September 2021,
              <http://www.3gpp.org/ftp/Specs/html-info/23501.htm>.

Authors' Addresses

   Satoru Matsushima
   SoftBank
   Japan

   Email: satoru.matsushima@g.softbank.co.jp


   Katsuhiro Horiba
   SoftBank
   Japan

   Email: katsuhiro.horiba@g.softbank.co.jp




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   Ashiq Khan
   SoftBank
   Japan

   Email: ashiq.khan@g.softbank.co.jp


   Yuya Kawakami
   SoftBank
   Japan

   Email: yuya.kawakami01@g.softbank.co.jp


   Tetsuya Murakami
   Arrcus, Inc.
   United States of America

   Email: tetsuya@arrcus.com


   Keyur Patel
   Arrcus, Inc.
   United States of America

   Email: keyur@arrcus.com


   Miya Kohno
   Cisco Systems, Inc.
   Japan

   Email: mkohno@cisco.com


   Teppei Kamata
   Cisco Systems, Inc.
   Japan

   Email: tkamata@cisco.com


   Pablo Camarillo Garvia
   Cisco Systems, Inc.
   Spain

   Email: pcamaril@cisco.com




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