TVR

Summary

The Time-Variant Routing (TVR) Working Group met at IETF 120. The session began with working group status updates showing significant progress on core milestones: use cases are complete, requirements and data models are currently in the RFC Editor's queue, and the applicability statement is progressing well. The group reviewed updates to active working group drafts and held discussions on two new personal drafts introducing proposed extensions to the TVR schedule YANG model.

Key Discussion Points

1. Administration and Working Group Status

Presenter: Chairperson
Slides: Chair Slides
Discussion:
- The Chairperson highlighted that TVR has made significant progress, with the requirements and data model documents now in the RFC Editor's queue.
- The working group previously determined that "implementation and operational considerations" is not a necessary milestone to keep, though a final consensus check will be taken on the mailing list.

2. Update of Off-Path Exposure Draft

Presenter: Luis M. Contreras
Slides: 01 - Update of draft-ietf-tvr-off-path-exposure
Draft: draft-ietf-tvr-off-path-exposure
Discussion:
- Luis M. Contreras presented the changes in version -02 of the draft, which is designed to help offload the processing of schedule changes from network elements to external controllers.
- Recent modifications include document cleanup, typo fixes, and the removal of several appendices. One removed appendix regarding potential gaps has motivated a new personal draft proposed today.
- The reference to the applicability draft must be updated to the newly adopted working group version. Once this change is reflected in version -03, the authors believe the draft is ready for Working Group Last Call (WGLC).

3. TVR Requirements Status

Presenter: Dan King
Slides: 03 - TVR Requirements Status
Discussion:
- Dan King provided a status update on the requirements document, noting that all open GitHub issues have been resolved.
- The draft received substantial feedback from various directorates. The authors removed standard RFC conformance language and clarified that not all requirements are mandatory because deployments vary drastically—from space and orbital environments to terrestrial energy-efficiency or campus network deployments.
- The draft has cleared the IESG, is entering the RFC Editor's queue, and will be used as a test case for the IETF GitHub publishing pilot.

4. Applicability of TVR YANG Data Models

Presenter: Leyuan Pan
Slides: 03-Applicability of TVR YANG Data Models
Draft: draft-ietf-tvr-applicability
Discussion:
- Leyuan Pan introduced updates in version -01, including welcoming Jin Wang as a new co-author.
- A new "early-aware mechanism" section was added to identify scheduled faults before execution (useful for stable topologies like satellite networks). Some informative references were also updated to normative.
- Per suggestions from Adrian Farrel, IP address examples were updated to utilize documentation ranges and IPv6.
- The Chairperson asked if the draft requires updates to align with final versions of the requirements and data model documents. Leyuan Pan confirmed that some updates will be applied after the meeting.
- Dan King suggested that the JSON examples in the draft could be leveraged for interoperability testing. He proposed exploring TVR extensions to open-source orchestration projects (such as ETSI TeraflowSDN or OSM) as a concurrent activity or for a future IETF hackathon. Luis M. Contreras and Leyuan Pan agreed to discuss this. Dan King also noted in the chat that he would start a thread on the list regarding potential interoperability.

5. Lifecycle and State Extensions for TVR Schedule YANG Model

Presenter: Luis M. Contreras
Slides: 04 - Lifecycle and State Extensions for TVR Schedule YANG Model
Discussion:
- Luis M. Contreras presented a new personal draft addressing administrative control over predefined schedules. While the base TVR model captures temporal validity, operators may need to administratively activate, suspend, deprecate, replace, or roll back schedules.
- This proposal introduces an optional augmentation containing administrative lifecycle attributes (states: pending, active, inactive, deprecated) and control parameters (version, priority, timestamp, origin).
- Don Fedyk inquired how "reality" is captured when the physical network drifts from the predicted schedule. Luis M. Contreras noted that while the draft details the scenario, there is currently no specific mechanism to capture drift in the model. The Chairperson suggested adding administrative reason codes to explain why a schedule is marked inactive.
- A participant questioned whether "priority" is the correct way to handle schedule conflicts, suggesting error notifications might be more appropriate. Luis M. Contreras noted that utilizing the "origin" parameter could help resolve conflicts.
- Lou Berger expressed support for the priority concept, as it allows a device to take action rather than simply failing to an error state. Lou also advised keeping administrative states separate from operational states (recommending a parallel operational state container), noting that an administratively "active" schedule may not be "operationally" active.

6. Time-Variant Routing Scheduling for Interconnection Scenarios

Presenter: Luis M. Contreras
Slides: 05 - Time-Variant Routing Scheduling for Interconnection Scenarios
Discussion:
- Luis M. Contreras introduced a speculative personal draft addressing BGP peering and multi-homing coordination. Existing automated tools do not allow operators to generically advertise future routing-relevant events.
- The draft proposes a schedule object for interconnection (including parameters like event type, affected entity, and suggested action) and explores off-path (APIs), on-path (BGP extensions), or hybrid transport mechanisms.
- The Chairperson asked whether this should remain an independent informational document or be folded into the existing working group applicability statement. Luis M. Contreras indicated that it might be better kept separate as it may drive work in other working groups (such as GROW or IDR).
- Don Fedyk raised concerns about how independent, autonomous domains would coordinate schedules without a centralized coordinator. Luis M. Contreras suggested it would operate similarly to BGP today, where each AS independently receives advertisements and computes its own routing view.
- Rick Taylor highlighted parallel work occurring in the Delay-Tolerant Networking (DTN) working group regarding scheduled contact windows and inter-domain peering, and suggested aligning these efforts.
- Scott Burley noted that adding probability or confidence metrics to scheduled events would be useful for network management and directing operator resources (e.g., flagging unexpected occurrences automatically).
- Eric suggested examining the "attachment circuits as a service" YANG model (which builds L2/L3 VPNs) to see if TVR scheduling can augment it. Lou Berger concurred with the suggestion.
- Gunter Van de Velde (Area Director) expressed reservations about whether this work fits within the current TVR charter and suggested consulting with the Operations Area ADs. He noted that coordinating future operator plans over BGP does not always work well in practice.

Decisions and Action Items

Action Item: Luis M. Contreras to update draft-ietf-tvr-off-path-exposure to version -03 with the correct reference to the adopted applicability statement. Once published, the chairs will initiate a Working Group Last Call (WGLC).
Action Item: Leyuan Pan to update draft-ietf-tvr-applicability to align with the final versions of the requirements and data model drafts.
Action Item: Dan King to start a mailing list thread regarding potential interoperability and implementation testing for the scenarios outlined in the applicability statement.
Action Item: Luis M. Contreras to coordinate with the Operations Area ADs regarding the appropriate home for the interconnection scenarios proposal.
Action Item: Luis M. Contreras to update the lifecycle and state extensions draft to address comments regarding the division between administrative and operational state, as well as handling reason codes for inactive schedules.

Next Steps

The chairs will run a formal consensus call on the mailing list to confirm the removal of the "implementation and operational considerations" milestone.

Automatic IETF Minutes

TVR