DMM

Summary

The Distributed Mobility Management (DMM) Working Group met at IETF 120. The session was chaired by Satoru Matsushima (co-chair Sri Gundavelli was unable to attend). The agenda focused on status updates for active working group documents, resolution of an IESG Discuss position, and several technical presentations detailing enhancements to the Mobile User Plane (MUP) architecture, Mobile Traffic Steering (MTS), and future SRv6 requirements for 5G/6G.

Key Discussion Points

Working Group Status & IESG Review

Presenter: Satoru Matsushima
Slides: WG Status
Discussion:
- Satoru updated the group on the TN-aware mobility draft, which currently has an active "Discuss" position from the Operations Area AD. The AD noted concerns that the draft presents itself as the sole mobility solution, whereas the IETF has previously published other solutions.
- John Kaippallimalil suggested that the wording can be clarified to resolve confusion regarding the "mobility-aware" aspects.
- Eric Klein pointed out that the document is Informational, reflecting a long-standing intent, and supported moving it forward once the new AD's concerns are addressed.
- Regarding 3GPP coordination, John Kaippallimalil recommended against sending a formal liaison to 3GPP SA2 on slicing, as SA2 is currently focused heavily on 6G and SA5 handles slicing.

A YANG Data Model for Attachment Circuit as a Service with UDP Tunnel Support

Presenter: John Kaippallimalil
Draft: draft-ietf-dmm-udp-tunnel-acaas-extn
Slides: A YANG Data Model for Attachment Circuit as a Service with UDP Tunnel Support
Discussion:
- John presented updates to the YANG model, which defines a Layer 3 bearer using a UDP tunnel. The model includes structures for upper/lower UDP port boundaries and ranges.
- The YANG structures have cleared operations area reviews with no compilation errors.
- Revision 01 was published to ensure compliance with RFC 9207 based on early review comments.
- Satoru noted that the draft is concise and ready for Working Group Last Call (WGLC).
Session Poll:
- Question: do you read this draft (udp-tunnel-acaas)?
- Result: yes: 3, no: 2, no_opinion: 3 (total: 22)

MUP Architecture v02 Update

Presenter: Satoru Matsushima
Draft: draft-ietf-dmm-mup-architecture
Slides: MUP Architecture v02 update
Discussion:
- Satoru presented the updates in revision 02, focusing on Section 7.5 (distributed home-routed roaming with multiple home operators).
- The architecture leverages two protocol updates:
  1. ST2 Route Update: Session Transformed Route (Type 2) can now steer packets to a destination interwork segment (such as N3 or N9 interfaces facing the 3GPP mobile system) by carrying an interwork segment extended community.
  2. MUP Extended Community: A new interwork segment type is defined to keep home operators' routing/addressing isolated, even with overlapping N9 address spaces.
- Section 9 (Security Considerations) was fully rewritten.
- Tom Hill commented on the security updates, noting that the evolving SRv6 Security Considerations draft should be referenced once it is near completion. Tom also advised caution when using the term "inter-domain" due to potential ambiguity and its interaction with the SRv6 trusted domain definition. Satoru clarified that this roaming scenario is for legacy roaming interconnection rather than inter-domain SRv6.

Mobile Traffic Steering

Presenter: Marco Liebsch (online)
Draft: draft-ietf-dmm-mts
Slides: Mobile Traffic Steering
Discussion:
- Marco summarized changes since adoption, noting that revision 02 incorporates feedback from reviews by John Kaippallimalil and Carlos Bernardos.
- The draft defines a framework and deployment options for mobile traffic steering using either a dedicated controller or decentralized control plane.
- It includes use cases such as Non-Terrestrial Networks (NTN), where user plane anchors are agile/moving, and nodes entering energy-saving/dormancy modes.
- The Information Model in the appendix is represented in a table format mapping key elements: traffic, path, User Plane Anchor (UPA), and Data Plane Nodes (DPN).
- Marco highlighted feedback from Luis Miguel Contreras Murillo regarding Time Variant Routing (TVR). The draft currently includes a pointer for proactive path changes, which could link to out-of-band TVR mechanisms to retrieve route change schedules without duplicating TVR attributes.
- Marco asked the WG for feedback on the NTN use case diagram and mapping details in Appendix B to 3GPP 6G TR 23.801.
Session Poll:
- Question: do you read this draft (mobile-traffic-steering)?
- Result: yes: 3, no: 3, no_opinion: 0 (total: 27)

Architecture Discussion on SRv6 Mobile User Plane

Presenter: Teppei Kamata
Draft: draft-ietf-dmm-srv6mob-arch
Slides: architecture-discussion-on-srv6-mobile-user-plane-03
Discussion:
- Teppei presented revision 03 of this informational draft, which explains why SRv6 is a strong fit for MUP by transforming mobile session info into IP routing.
- The main update in version 03 is the clarification of the SRv6 micro-segment (NEXT-C-SID flavor, RFC 9800) and its benefits (reducing encapsulation overhead, optimizing MTU impact, and improving packet efficiency for slicing, edge computing, and URLLC).
- John Kaippallimalil suggested adding more details on how the transition from session-based $O(N^2)$ scaling to routing-based $O(N)$ scaling is achieved through the session controller.
- Tingji Ge asked how any-to-any communication is simplified. Teppei clarified that SRv6 MUP converts session-based point-to-point state tracking into destination-based IP routing, reducing the state tracking requirement.
Session Poll:
- Question: do you read this draft(architecture discussion of srv6mup)?
- Result: yes: 7, no: 3, no_opinion: 0 (total: 29)

Mobile User Plane Evolution: 5G & 6G

Presenter: Tingji Ge
Slides: Mobile User Plane Evolution: 5G & 6G
Discussion:
- Tingji presented on the 3GPP 6G User Plane architecture study (TR 23.801).
- Key tasks in 3GPP include improving multi-vendor interoperability (by disaggregating CP and UP features, such as buffering and end-marker construction) and enhancing UP flexibility/resilience (by splitting UPFs into Serving UPFs and Anchor UPFs).
- The 3GPP study references IETF CATS (Computing-Aware Traffic Steering) and draft-ietf-dmm-mts for traffic steering.
- There are ongoing discussions in 3GPP regarding GTP-U over SRv6 vs. native SRv6 replacing GTP-U.
- An unnamed participant questioned the contradiction between 3GPP's transport-agnostic requirements and proposals to natively replace GTP-U with SRv6. Tingji noted that native SRv6 replacement remains an active proposal under discussion.
- Satoru Matsushima questioned whether SRv6 over MPLS would be required if transport-agnostic goals are maintained.
- Eric Klein commented on the possibility of a partial GTP-U replacement to integrate edge computing, suggesting that IETF network experts should provide architectural proposals to 3GPP.

Requirements of SRv6 for 6G User Plane

Presenter: Xiaohu Xu
Slides: Requirements of SRv6 for 6G User Plane
Discussion:
- Xiaohu presented an individual draft analyzing SRv6 requirements for 6G user planes.
- The draft reviews GTP-U limitations (fixed paths, high reconfiguration latency, coarse QoS granularity) and lists key 6G requirements: dynamic topology support, fine-grained traffic isolation, deterministic latency, and native inbound telemetry.
- Xiaohu detailed how SRv6 path, service, and application programmability satisfy these demands and highlighted necessary control plane coordination between 3GPP CP (SMF/AMF) and the transport controller.
- John Kaippallimalil asked if multi-domain roaming scenarios had been analyzed. Xiaohu planned to incorporate roaming analysis in future updates.
- Eric Klein proposed sending a liaison to 3GPP to share the IETF's discussions on 6G user plane requirements. Satoru Matsushima agreed to facilitate cooperation.

Decisions and Action Items

draft-ietf-dmm-udp-tunnel-acaas-extn: Satoru Matsushima to initiate a Working Group Last Call (WGLC) on the mailing list.
draft-ietf-dmm-srv6mob-arch: Satoru Matsushima to initiate a WGLC on the mailing list.
draft-ietf-dmm-mup-architecture: Satoru Matsushima to update the security considerations section to reference the upcoming SRv6 security considerations draft and clarify "inter-domain" terminology as suggested by Tom Hill.
6G Coordination: Satoru Matsushima requested Tingji Ge and Xiaohu Xu to collaborate on aligning their 6G transport requirements and study efforts.

Next Steps

Authors of draft-ietf-dmm-mts to address feedback regarding TVR coordination, Appendix B mapping, and NTN use-case diagrams before the next meeting.
Chairs to coordinate potential liaison activities with 3GPP regarding 6G data plane discussions.

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