MOQ Wiki

Joining Fetch Dissent

2 min read

A cluster of open issues and competing proposals around how subscribers join a live stream mid-session. Tagged “Joining Fetch Dissent” on GitHub.

The Problem

When joining a live stream, a subscriber needs historical data (e.g., the latest keyframe) to start rendering. The current joining-fetch mechanism has been contentious, generating multiple alternative proposals.

Open Issues (tagged “Joining Fetch Dissent”)

  • #1313 - Joining FETCH as separate control message creates edge cases and feature gaps (ianswett, Past Deadline)
  • #1391 - Unclear how to use Joining FETCH with New Group Request (ianswett)
  • #1386 - Can a publisher ‘lie’ about what Largest Object is? (ianswett)
  • #1358 - Subscribing to start of current Group could be optimized (ianswett)
  • #1039 - Simplifying joining at the latest available join point (wilaw)
  • #1023 - Subgroups + DELIVERY_TIMEOUT = pathological FETCH (afrind, Past Deadline)

Competing Proposals

  1. Current Joining Fetch (in draft-17) - Separate FETCH alongside live SUBSCRIBE
  2. PR #1362 - Prior Group Subscription Filter (ianswett) - Filter-based approach
  3. Subscribe Rewind (martin-duke) - Extend SUBSCRIBE with a Rewind subscription filter for best-effort past group retrieval (draft-02 published Apr 2)
  4. Join Subscription Filters (alan-frindell) - Filter-based join point selection. Alan says his is “more of an extension to Martin’s.”

Latest Developments

  • draft-duke-moq-subscribe-rewind-02 (Apr 2) - Updated Rewind draft published with refined subscription filter semantics
  • PR #1604 (Apr 10) - martin-duke implements the #1602 proposal to move Joining FETCH onto the SUBSCRIBE/PUBLISH stream. alan-frindell reviewed, noting subscriber priority cannot differ between fetch and subscription.
  • #1603 (Apr 10-11) - martin-duke questions required-request-id. Ian Swett supports simplification, calling it unclear what functionality it provides. He also notes Joining FETCH’s dependency on another Request as a design concern.
  • #1602 (Apr 9) - martin-duke proposes moving Joining Fetch to SUBSCRIBE/PUBLISH stream, eliminating race conditions
  • #1601 (Closed) - Race condition in current design
  • Restriction requiring “largest object” subscribes was removed
  • Interim moq-13 (Apr 13) has REWIND slides on the agenda

Related

Graph View

DraftsConceptsPeopleImplDiscInteropOtherTags
DraftsConceptsPeopleImplDiscInteropOtherTags

Backlinks