**Session Date/Time:** 27 Mar 2023 06:30

# tvr

## Summary
The inaugural meeting of the Time-Variant Routing (tvr) working group focused on defining scope, goals, and identifying potential areas of collaboration. Presentations covered use cases, existing time-variant information models (Aeronautical Information Exchange Model - AIXM), network traffic examples, contact graph routing (CGR), forwarding policies, and the use of ALTO for exposing time-variant routing information. The session concluded with a call for participation in drafting Internet drafts to address the working group milestones.

## Key Discussion Points
*   **Use Cases:** Discussion of use cases including local resource preservation, adapting to external conditions (e.g., power, comm), and predicted mobility. There was consensus on creating a use case document as an informational product of the working group.
*   **AIXM Temporal Model:** Introduction of the AIXM temporal model as a potential source of inspiration for time-variant information modeling. Focus was on its ability to convey state as a function of time, absolute vs. periodic time, and the separation of information producers and consumers. Limitations regarding parameter interrelation and planning horizon were noted.
*   **Network Traffic Use Cases:** Discussion of network traffic patterns that vary over time, such as traffic surges due to events, link upgrades, and device failures. These use cases motivate the need for time-variant routing to optimize resource utilization.
*   **Contact Graph Routing (CGR):** Overview of CGR's history and its application in delay-tolerant networking, particularly in space communications. CGR utilizes contact plans, which are schedules of communication opportunities between nodes.
*   **Forwarding Policies:** Exploration of forwarding policies related to bundle protocol and IP, including policies for handling full memory stores, new route installations, and packet expiration. The suitability of applying IP-specific policies was questioned, and the potential for the DTN working group to take on this work was discussed.
*   **Contact Plan Data Model:** Proposal for standardizing a data model and file format for contact plans, enabling comparison, revisions, and archiving. JSON was presented as an example encoding.
*   **ALTO for Time-Variant Routing:** Discussion of using ALTO (Application-Layer Traffic Optimization) to expose time-variant routing information to applications. ALTO's calendar cost feature could be leveraged to provide both current and future views of routing costs.
*   **Probability of Schedules:** The topic of accounting for uncertainty and probability of calendars and schedules being correct was brought up.

## Decisions and Action Items
*   **Decision:** The working group will create a use case document as an informational product.
    *   **Action Item:** Volunteers are requested to help author the use case document; coordinate on the mailing list.
*   **Action Item:** Participants to review the AIXM temporal model and discuss its applicability to tvr on the mailing list.
*   **Action Item:** Explore how to express parameters as a function of time, either time position, or another input parameter.
*   **Action Item:** Participants to discuss the scope of forwarding policies (IP vs. bundle protocol) on the mailing list.
*   **Action Item:** Refine the data model for contact plans, taking into account comments on the list of destinations, mandatory start/end times, and bandwidth/latency considerations.
*   **Action Item:** Explore how to handle more dynamic parameter definitions and better understand link attributes for time variant routing schedules.

## Next Steps
*   Actively participate in discussions on the mailing list to refine requirements and identify areas of collaboration.
*   Form groups to work on consolidated Internet drafts addressing the working group milestones (problem statement, use cases, requirements, information model, data model, applicability statements, considerations).