Internet DRAFT - draft-zzhang-dmm-anup5g-signaling
draft-zzhang-dmm-anup5g-signaling
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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Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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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