Session Date/Time: 05 Nov 2025 21:00

TVR Working Group - IETF 124 Meeting Minutes

Summary

The TVR Working Group meeting at IETF 124 focused on the status of its chartered items, specifically the requirements, applicability, and off-path exposure documents. A significant discussion revolved around the necessity and scope of a potential "Implementation and Operational Considerations" document. Updates were provided on the "TVR off-path exposure" and "TVR Applicability" drafts, with calls for working group adoption or further review initiated. The "TVR Requirements" document, after incorporating recent comments, will undergo a second Working Group Last Call due to the nature of the changes. The working group also considered whether there was any interest in new work or additional milestones, with no new proposals emerging during the session.

Key Discussion Points

Status of Chartered Items:
- RFC 9657 (Initial Use Case document) is published.
- The Requirements document is ready for IESG review, pending a shepherd's write-up.
- Data Model and Applicability Statement are underway.
- Work on "Implementation and Operational Considerations" (I&O) has not yet begun.
Discussion on Implementation and Operational Considerations Document:
- Utility Question: The Chair asked if the working group still believes there is utility in documenting implementation and operational considerations for using the data model or applicability statement.
- Rick Taylor's Clarification: Distinguished between integrating YANG extensions for timing information (I&O) and what a routing protocol should do with this information (Applicability Statement). The I&O document should focus on "potholes found during implementation."
- Greg Murski's Point: Highlighted time synchronization (e.g., clock type, accuracy, resolution) as a crucial operational consideration. The requirements document currently lacks specific requirements or presumptions for time synchronization.
- Call for Input: The Chair emphasized that if there is implementation experience and interest in writing such a document, participants should engage on the mailing list. The question of potentially removing this milestone altogether was raised.
Update on "Using Off-Path Mechanisms for Exposing Time-Variant Routing Information" (draft-tvr-off-path-exposure):
- Rename: The draft was renamed to "TVR off-path exposure."
- Updates: Appendix A (assessment of ALTO against TVR requirements) was updated, and new comments/reviews were solicited on the mailing list with no feedback received so far, suggesting stability.
- Alternatives for Off-Path Solutions: The document currently refers to ALTO, network controllers (via API), and managing devices/scheduled databases (as per applicability draft). A question was raised about other potential options and the specific mechanisms (e.g., TVR YANG model) for controllers/managing devices.
- Draft Cleanup: The author (Luis M. Contreras) proposed removing Appendix B (assessment of architectural proposal in previous applicability draft) and Appendix C (identifying gaps on TVR specifications, deemed useful for ALTO but not the current document). Decision pending on Appendix A (ALTO assessment) and Appendix D (implementation status).
- Identified Gaps (Appendix D): Luis clarified that gaps included items like signaling the removal of groups of links (e.g., an entire line card), not just individual nodes/links. The Chair stressed the importance of identifying any missing technical materials relevant to existing documents (requirements, data model) sooner rather than later on the mailing list.
Update on "TVR Applicability" (draft-ietf-tvr-applicability):
- Updates (based on IETF 123 comments):
  - Removed the requirement for a specific communication time in Section 6.1.
  - Added a general discussion in Section 6.6 that managing and managed devices within a scheduled domain should be synchronized to the same time source.
  - Clarified in Section 6.4.1 that if two schedules conflict but have the same Schedule ID, the latest one should be considered an update and used.
- Chair's Questions:
  - Asked about assumptions regarding out-of-order delivery when updating schedules with the same ID.
  - Confirmed that decentralized schedule generation would remain out of scope for this document, as no clear use case had emerged.
- Working Group Adoption: The Chair indicated a call for working group adoption would be taken to the mailing list.
Update on "TVR Requirements" (draft-ietf-tvr-requirements):
- Brian Sepos's Presentation: Discussed minor changes following the last call.
- Multiple Time-Variant Domains: Explicitly called out and explained the concept of multiple TVR domains (e.g., universal vs. individual device domains) and how schedules between different domains do not relate.
- Time Synchronization and Margins: Added discussion on characterizing device clocks (precision, accuracy) and the need for schedule generators to accommodate these using "margins." Margins cover both clock limitations and propagation delays for administrative changes.
- Rick Taylor's Margin Question: Asked if the same margin value is used for clock drift and reaction time. Brian clarified that the document leaves this to system design and implementation, calling out margin as a necessary consideration.
- Greg Murski's Resolution Question: Asked if there are expectations for clock resolution/accuracy units. Brian reiterated that the document focuses on considering precision and accuracy rather than imposing specific units or levels of detail, leaving it to system design. Luis M. Contreras added that accuracy would likely be use-case driven. Lee indicated the applicability draft provides different synchronization mechanisms for selection based on requirements.
- Decision on Last Call: Due to the nature of the changes (adding new subsections), the Chair decided to conduct one more Working Group Last Call for this document, acknowledging that it might not have been strictly necessary but opting for prudence.
Open Mic for Future Work:
- The Chair opened the floor for discussion on additional work, new documents (e.g., I&O considerations), or future charter items.
- No new proposals or interest in additional work emerged.

Decisions and Action Items

TVR Requirements Document: Will undergo another Working Group Last Call on the mailing list. All participants are encouraged to review the updated document.
TVR Applicability Document: A Working Group Adoption call will be issued on the mailing list.
Implementation and Operational Considerations Document: The fate of this chartered item will be discussed further on the mailing list. Input and potential volunteers with implementation experience are encouraged to provide feedback.
Shepherd's Write-up: The Chair will complete the shepherd's write-up for the Requirements document pending the new WG Last Call.
Off-Path Exposure Document Cleanup: Authors to proceed with cleaning up appendices as discussed, and then a new version will be created for progression.

Next Steps

Chairs to initiate the Working Group Last Call for the "TVR Requirements" document.
Chairs to initiate the Working Group Adoption call for the "TVR Applicability" document.
Continue discussion on the mailing list regarding the "Implementation and Operational Considerations" document.
Monitor progress of data models through various reviews.
Next TVR Working Group meeting at IETF 125.