ANUP Implementation in 5G with BGP Signaling
draft-zzhang-dmm-anup5g-signaling-01

dmm                                                             Z. Zhang
Internet-Draft                                          Juniper Networks
Intended status: Informational                                  K. Patel
Expires: 9 August 2024                                            Arrcus
                                                         6 February 2024

              ANUP Implementation in 5G with BGP Signaling
                  draft-zzhang-dmm-anup5g-signaling-01

Abstract

   Draft-zzhang-dmm-mup-evolution describes an architecture in which co-
   located Access Node and User Plane Function node of a 5G mobile
   network are integrated into a single Network Function ANUP in 6G for
   simplified signaling and optimized forwarding.  The integration can
   happen in 5G as well but only with optimized forwarding.  This
   document describes how BGP signaling specified in Draft-mpmz-bess-
   mup-safi can be used for ANUP implementation in 5G.

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   This Internet-Draft will expire on 9 August 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  ANUP with MUP Controller and BGP Signaling  . . . . . . . . .   3
     2.1.  With Route Lookup in the DN Routing Instance  . . . . . .   3
     2.2.  Avoiding DL Route Lookup  . . . . . . . . . . . . . . . .   3
     2.3.  Avoiding UL Route Lookup  . . . . . . . . . . . . . . . .   4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Access Node User Plane (ANUP) Network Function in 6G as proposed
   in [I-D.zzhang-dmm-mup-evolution] integrates co-located Access Node
   and UPF function into a single NF, so that signaling can
   significantly simplified and data plane significantly optimized
   because no N3 tunneling is needed anymore.

   The signaling simplification is only expected in 6G.  In 5G, the data
   plane optimization can still be realized with integrated AN and UPF
   function even though separate N2 and N4 signaling are still used.
   The ANUP can run N2 to AMF and N4 to SMF simultaneously, and the
   correlation of N2 and N4 signaling allows the ANUP to install UL/DL
   forwarding state w/o GTP tunneling:

   *  UL traffic is directed into to the routing instance for the DN
      after Access Network encapsulation header (e.g. radio protocol
      headers) is removed, as if the GTP-U header was removed on a
      traditional UPF.

   *  For DL traffic in the routing instance for the DN, a route lookup
      produces Access Network encapsulation information (e.g. radio
      protocol headers) for a PDU session, as if the traffic just
      arrived via GTP-U and the TEID was used to produce the same
      information.

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   While the above work with separate N2/N4 signaling on the same ANUP,
   it does require the SMF to interfaces with many ANUPs - a changed
   deployment model.  An alternative is to use the MUP Gateway
   architecture described in [I-D.mhkk-dmm-srv6mup-architecture], in
   which the SMF only interfaces a few apparent central UPFs, though a
   "central UPF" is actually a collection of a MUP controller and a set
   of distributed MUP GWs and MUP PEs.

2.  ANUP with MUP Controller and BGP Signaling

   In this model, the ANUP is the integration of an Access Node (e.g.,
   gNB) and a MUP GW.  GTP/N3 tunneling is no longer needed - DL traffic
   in the routing instance for the DN routes directly to radio protocol
   encapsulation for the session, and UL traffic is directed to the VRF
   for the DN after the radio protocol encapsulation is removed.

2.1.  With Route Lookup in the DN Routing Instance

   For UL traffic, the <UPF address, TEID> tuple received in N2
   signaling for a PDU session is matched against a Session Transformed
   Route Type 2 (ST2) route [I-D.mpmz-bess-mup-safi] to determine the
   routing instance for the PDU session's DN, and UL traffic is then
   directed to the routing instance for further route lookup.

   For DL traffic, the <AN address, TEID> tuple sent in N2 signaling for
   the PDU session is matched against a Session Transformed Route Type 1
   (ST1) route to install a UE prefix route in the routing instance with
   the forwarding nexthop being radio protocol encapsulation for the PDU
   session.

2.2.  Avoiding DL Route Lookup

   With the MUP GW architecture, DL traffic arriving on a MUP GW may be
   with an SRv6 destination address with the End.GTP4/6.E behavior.  The
   MUP GW would construct a GTP-U header accordingly and send
   encapsulated traffic to the AN.

   With an ANUP integrating a MUP GW and AN, there is no need for GTP-U
   - the SRv6 end point behavior would be a new one that directly maps
   the decapsulated traffic to the radio protocol encapsulation
   information for the PDU session identified by the TEID in the SRv6
   address.  Notice that the TEID is allocated by the ANUP and sent in
   the N2 signaling (and then signaled back via ST1 route).

   In case of MPLS, the DL traffic starts with a GTP-U header (after the
   MPLS label stack).  The TEID in the header, like in the SRv6 case,
   identifies the PDU session so the packet can be forwarded directly w/
   o inner header lookup or GTP-U encapsulation.

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   This is as if the GTP-U tunnel was replaced with an SRv6/MPLS tunnel.

   Note this can happen with or without a routing instance for the DN.

2.3.  Avoiding UL Route Lookup

   Similarly, UL route lookup may also be skipped.  For a PDU session,
   the <UPF address, TEID> tuple received in the N2 signaling is matched
   against an ST2 route, which carries information for the DN.  If there
   is no local routing instance for the DN, a Direct Segment Discovery
   route from a remote MUP PE is matched and PDU session traffic is
   forwarded to that remote MUP PE according to the Direct Segment
   Discovery route.

3.  Security Considerations

   There are no additional security implications compared to the MUP
   architecture in [I-D.mhkk-dmm-srv6mup-architecture] and
   [I-D.mpmz-bess-mup-safi].

4.  Acknowledgements

   The authors thank Arda Akman and Constantine Polychronopoulos for
   their review/comments/suggestions to make this document and solution
   more complete.

5.  References

5.1.  Normative References

   [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,
              <https://datatracker.ietf.org/doc/html/draft-mhkk-dmm-
              srv6mup-architecture-06>.

   [I-D.mpmz-bess-mup-safi]
              Murakami, T., Patel, K., Matsushima, S., Zhang, Z. J.,
              Agrawal, S., and D. Voyer, "BGP Extensions for the Mobile
              User Plane (MUP) SAFI", Work in Progress, Internet-Draft,
              draft-mpmz-bess-mup-safi-03, 5 November 2023,
              <https://datatracker.ietf.org/doc/html/draft-mpmz-bess-
              mup-safi-03>.

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   [I-D.zzhang-dmm-mup-evolution]
              Zhang, Z. J., Patel, K., Contreras, L. M., Islam, K.,
              Mutikainen, J., Jiang, T., Jalil, L., Sejati, O. P., and
              S. Zadok, "Mobile User Plane Evolution", Work in Progress,
              Internet-Draft, draft-zzhang-dmm-mup-evolution-06, 10 July
              2023, <https://datatracker.ietf.org/doc/html/draft-zzhang-
              dmm-mup-evolution-06>.

5.2.  Informative References

   [_3GPP-23.501]
              "System architecture for the 5G System (5GS), V17.3.0",
              December 2021.

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks
   Email: zzhang@juniper.net

   Keyur Patel
   Arrcus
   Email: keyur@arrcus.com

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