TVR

IETF 125 - TVR Working Group Minutes

Date: Tuesday, March 17, 2025
Chairs: Tony Li, Ed Birrane, Adam Wiethuechter
AD: Gunter Van de Velde
Minutes: Daniel King, Ed Birrane

Summary

The TVR working group met at IETF 125 to discuss the status of core documents, updates to the requirements draft, the applicability of TVR YANG models, and new research into path verification for LEO satellite networks. The Use Cases document is complete, and both the Requirements and Data Model drafts are currently under IESG review.

Key Discussion Points

Working Group Status and Milestones

Tony Li opened the meeting, noting that the Use Cases are finalized. The Requirements and Data Model documents are with the IESG, though slightly behind the original milestones. The current focus has shifted to the Applicability Statement and implementation/operational considerations.

Time-Variant Routing (TVR) Requirements

Daniel King presented updates on the TVR requirements document.

Status: The document is mature and has received several directorate reviews (notably from Bo Wu). A Security Directorate review (assigned to Frank Xialiang) is still pending.
Updates: Recent changes focused on clearing ambiguity, defining external interfaces (Orchestrators, SDN controllers, PCEs), and precision for time synchronization. New text was added regarding resource preservation and dynamic reachability to clarify that TVR handles scheduled changes, while ancillary technologies handle unplanned changes.
Discussion: Fonyan asked about diagnostic requirements (ping/traceroute). Daniel King noted that while high-level operational considerations like clock sync are included, fine-grained diagnostic mechanisms are likely better suited for the applicability or operational considerations documents. Ed Birrane (remote) emphasized that addressing the Security review is a priority before final publication.

Applicability of TVR YANG Data Models

Sule Zhang presented the applicability statement for the TVR YANG models.

Content: The draft defines the roles of Managing Device (schedule generation), Network Controller (routing computation), and Managed Device (execution). It introduces the concept of "Maximum Acceptable Time Error Bound" for synchronization.
Operational Details: The draft suggests using the intended data store for schedule provisioning and the operational data store for execution status. It defines a "last known good" policy for schedule conflicts.
Discussion: Daniel King suggested coordinating with the TeraFlowSDN (TFS) project for experimental implementation, specifically regarding energy-aware networking. Tony Li and Ed Birrane discussed the document's scope, concluding that the operational and security considerations milestones should be folded into this applicability draft rather than creating a separate document, provided the content remains manageable.

Segment-Based Path Verification in Low-Earth Orbit Satellite Networks

Yuxuan Wu presented a proposal for verifying paths in LEO satellite networks (SNs).

Problem: Traditional terrestrial path verification (delay-based or crypto-based) struggles with LEO dynamics. Linear delay-distance relationships do not hold in SNs, and hop-by-hop crypto can be computationally expensive for large constellations.
Proposal: A segment-based approach using satellite relays to verify consecutive segments of a path rather than the entire end-to-end chain at once.
Discussion: Tony Li questioned the necessity of verification if the path is computed to avoid "risk areas" by construction (CSPF). Yuxuan Wu and Ed Birrane clarified the threat model involves traffic hijacking or compromised forwarding where the physical path might deviate from the computed path. Lin Han noted that since satellite links are "open" compared to closed terrestrial fibers, verification is more critical, though many basic protocol questions (IP vs. MPLS in LEO) remain. Fonyan suggested injecting metadata into packet headers during forwarding to align the real path with the intended path.

Decisions and Action Items

Requirements Document: The chairs and authors will follow up with the Security Directorate to secure a review for the requirements draft.
Applicability Statement: A formal call for working group adoption of the applicability draft will be issued on the mailing list.
Document Consolidation: The working group reached a tentative consensus to include implementation and operational considerations within the applicability draft rather than spinning up a new document.

Next Steps

Poll the mailing list for adoption of the applicability statement.
Continue refining the applicability draft with more detailed JSON examples and operational scenarios.
Review the segment-based path verification proposal for potential inclusion in future work items or as a standalone contribution.