IETF MOQ WG: Top Tracks and SSTS (or ABR in general)

Message Snapshot

• List: moq@ietf.org
• Thread subject: Top Tracks and SSTS (or ABR in general)
• Message subject: [Moq] Re: Top Tracks and SSTS (or ABR in general)
• Author: Law, Will
• Published: 2026-07-28T09:48:43.000Z
• Source tag: ietf-mailing-list
• Message URL: Open in IETF Mail Archive

Summary

Law, Will posted to the MOQ working group mailing list on July 28, 2026. YuYou�s summation is correct. Top-tracks would be the discovery mechanism for the tracks (similar to SUBSCRIBE_NAMESPACE, which is another entry p…

Why It Matters

This message came from the public MOQ working group archive and captures active discussion, meeting coordination, or implementation feedback around Media over QUIC.

Message Excerpt

YuYou�s summation is correct. Top-tracks would be the discovery mechanism for the tracks (similar to SUBSCRIBE_NAMESPACE, which is another entry point). Once the client receives the PUBLISH message for these tracks, it allocates them to a switching set using the SWITCHING_SET_ASSIGMENT parameter in the PUBLISH_OK mess…

Plain-Text Body

YuYou�s summation is correct. Top-tracks would be the discovery mechanism for the tracks (similar to SUBSCRIBE_NAMESPACE, which is another entry point). Once the client receives the PUBLISH message for these tracks, it allocates them to a switching set using the SWITCHING_SET_ASSIGMENT parameter in the PUBLISH_OK message.

However, in my expectation, the uses of SSTS will not be so dynamic in their selection of constituent tracks. Since the publisher must produce the ABR variants and these must be coupled with some playback mechanism, I think SUBSCRIBE_NAMESPACE and plain SUBSCRIBE will be the majority use-case and entry point for SSTS behaviors.

Conceptually what is interesting to me is that Top-tracks is a filter, but so is SSTS. SSTS always filters to one track, based on a condition (in algo 0, the throughput). We could, if we wanted to, extend Top-tracks to apply a class of optional conditional filters. This would not be difficult. The set assignment would be handled by Top-tracks. Then the parameters (rank, weight and throughput threshold) would need to be added as reserved properties on the tracks by the original publisher. With these in place, we would just need one more flag in Top-tracks to say �apply SSTS to the filtered tracks�. In fact I would stop calling it �Top-tracks �, as �top� is just one way to filter tracks. If we renamed it �TRACK-FILTERS�, then Top-N could be one mode of filtering and SSTS could be an output option.

Cheers Will

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Chief Architect - Cloud Technology Group Akamai Technologies Switzerland Mobile +41 79 535 07 94

From: Yu You (Nokia) yu.you@nokia.com Date: Tuesday, 28 July 2026 at 10:42 To: Ian Swett ianswett=40google.com@dmarc.ietf.org; MOQ Mailing List moq@ietf.org Cc: Mo Zanaty mzanaty@cisco.com; Law, Will wilaw@akamai.com Subject: Re: [Moq] Top Tracks and SSTS (or ABR in general)

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Here is my understanding and polished by AI when applying both Top Track filter and SSTS.

When Sender-Side Track Switching (SSTS) is applied to tracks selected by a Top-N filter, the result is that the subscriber receives exactly one track at a time, effectively narrowing the "Top-N" pool down to a "Top-1" delivery.

However, rather than an "override," these two mechanisms work in a coordinated, two-step pipeline:

1. Step One: The Top-N Filter Defines the Pool

The Top Tracks Filter acts as a discovery and promotion mechanism. It evaluates all tracks in a namespace and promotes the (N) tracks with the highest property values (such as bitrate or popularity) to the selected state.

• The publisher sends a PUBLISH message for each of these (N) tracks to initiate subscriptions.
• At this stage, (N) tracks are authorized and available for delivery to the subscriber.

2. Step Two: SSTS Performs the Final Selection

Once the tracks are promoted by the Top-N…