Session Date/Time: 10 Nov 2021 16:00

dmm

Summary

The dmm working group session included updates on existing working group documents, discussions on proposed revisions, and a presentation on a new individual submission. Key topics revolved around clarifying the scope of slicing-related work to avoid conflicts with 3GPP, resolving outstanding comments from a Working Group Last Call, and introducing an SRv6-based architecture for mobile user plane optimization. The working group aims to address critical comments and move forward with documents towards publication.

Key Discussion Points

Working Group Document Status:
- User Plane Protocol and Architecture Analysis: No significant progress since the last meeting; a new revision is requested.
- Segment Routing IPv6 for Mobile User Plane (SRv6-MUP): The document underwent a Working Group Last Call (WG LC), but several concerns and active discussions emerged. A plan is in place for authors to resolve outstanding comments with reviewers, with a goal for a quick re-last call in January.
- Mobility Aware Transport Network Slicing for 5G (MATNS): Recently adopted, the document had updates based on adoption call comments and routing working group feedback. Authors presented clarifications on architecture (informational, not changing 3GPP), transport endpoint relation to 3GPP 28541, and refinement of the MTNC-ID to focus on traffic classes and tenants, explicitly removing ties to a specific path.
- SRv6 Mobile User Plane Architecture (New Submission): An individual submission proposing an SRv6-based architecture for optimizing the 5G user plane was presented.
MATNS Document Discussion (John):
- Clarified that the document makes no changes to the 3GPP N4 interface or SMF/UPF functions.
- The core intent is to define a mapping or association between a mobile session and a transport slice, not to define the transport slice itself, respecting work in other SDOs/WGs.
- AD Feedback (Eric Cline): Suggested considering broader IETF "slice" work (e.g., 6man VTN ID) and ensuring cross-working group coordination. Authors acknowledged the need to review text for clarity, add informative references to other work, and maintain neutrality.
- Authors confirmed aligning with TEAS WG and encoding MTNC-ID in UDP ports for neutrality.
- An IPR concern was noted regarding the draft's link to an individual draft.
SRv6-MUP WG LC Feedback Discussion (Pablo):
- The document has progressed to revision 17, addressing many editorial and technical comments.
- Joel's Blocking Comment: Joel Harper expressed concern that certain sections (specifically, alternatives in section 5 and behaviors in section 6) implicitly redefine gNodeB and UPF behavior, which is the domain of 3GPP. Authors argue they are defining data plane tools and not deprecating 3GPP's work or redefining its interfaces. The chairs echoed the principle that IETF should not redefine 3GPP architecture, but can define alternative interfaces.
- Jeffrey's Ongoing Comments: Extensive technical and editorial feedback from Jeffrey was acknowledged, with good progress. Remaining issues include clarification on "drop-in" mode and consistent use of U1:TID for addressing in examples. Jeffrey stressed not changing 3GPP signaling/architecture while allowing SRv6 tunnels for specific deployments.
- AD Suggestion (Eric Cline): Proposed making the contentious examples in section 5 non-normative or moving them to an appendix, as the normative core is section 6 (segment endpoint behaviors).
SRv6 Mobile User Plane Architecture Discussion (Satoru):
- Presented a new individual draft for an SRv6-based architecture to optimize 5G user plane paths for latency, TE, and slicing.
- Emphasized that it does not change the 3GPP architecture. Instead, an SR network directly forwards packets through n3/n6.
- Control Plane: Utilizes an MEP controller (translating session info to routes) and MEP gateways/PEs (using BGP for route exchange).
- Data Plane: SR network with gateways/PEs.
- Scope Clarification: Steering is primarily on the N6 interface (data network side), with 3GPP not recognizing nodes north of the UPF's N6.
- Relation to other drafts: Discussed conceptual overlaps with "MFA" (anchorless mobility, N6 steering) and Marco's mobility ID. The authors indicated this work is based on their network deployment and is neutral to specific control plane interfaces.
- Technical Questions:
  - John Hanno: Inquired about the impact on UPF functions (charging, access control, slicing for multiple DNNs) if n3/n6 steering is involved. Authors stated the architecture fulfills DMM requirements, with other functions managed by the mobility management system.
  - Hanu: Raised concerns about the scalability and reactiveness of routing protocols like BGP when propagating rapidly changing session-level steering information.
  - Ding Li: Asked about handling N9 interfaces with multiple UPFs and the architecture's fit with 3GPP SA2's MBUPF/multicast (5G MBS), which is not currently covered.

Decisions and Action Items

SRv6 for Mobile User Plane (draft-ietf-dmm-srv6-mobile-user-plane):
- Authors (Pablo et al.) to work offline with reviewers (Joel, Jeffrey) to resolve all outstanding comments, specifically regarding the relationship with 3GPP specifications and normative text.
- The chairs will aim for a short Working Group Last Call in January if issues are resolved.
Mobility Aware Transport Network Slicing for 5G (draft-ietf-dmm-mobility-aware-transport-network-slicing):
- Authors (John et al.) to refine the document's text to clearly articulate its scope, emphasize the mapping/association aspect, and add informative references to relevant work in other working groups (e.g., TEAS, 6man).
- Authors should ensure the document maintains neutrality regarding specific identifiers from other groups.
- The chairs will consider cross-working group review for this document once the text is sufficiently clarified.
User Plane Protocol and Architecture Analysis:
- Chairs to reach out to the authors to request a new revision and discuss document progress.

Next Steps

The chairs will distribute the meeting notes.
The dmm working group will continue discussions on the mailing list for the "Mobility Aware Transport Network Slicing for 5G" document.
The Area Director (Eric Cline) will consider facilitating cross-working group coordination for "slicing" related work across relevant IETF WGs.
The new individual submission, "SRv6 Mobile User Plane Architecture," will gather feedback from the working group, with no immediate working group status.