draft-vvv-moqt-object-acks-00 | Individual submission | -00 posted 2026-11-02 (IETF 127 deadline) | 8 pages | expires 2027-05-06 | Datatracker
Authors
- Victor Vasiliev (Google)
Abstract
A moq-transport extension that lets a subscriber acknowledge each object it has received and processed. Each acknowledgement carries a time delta from an application deadline, so the publisher gets a direct signal for publisher-side bitrate adaptation. QUIC’s own ACKs don’t serve this purpose: the W3C WebTransport API does not expose them, and a QUIC ACK only means the bytes arrived, not that the application processed them. Vasiliev said on the list (Nov-2, “MOQT Object ACKs”) that this writes up a mechanism already implemented in Google’s MOQT stack (quiche moqt).
Key Technical Details
- Negotiation: a
SUPPORT_OBJECT_ACKSSETUP Option (0 or 1; enabled only if both sides send 1). The draft defines it for draft-22 only, over both raw QUIC and WebTransport. - Per subscription: an
OBJECT_ACK_WINDOW_SIZEparameter (µs; 0 = off) in SUBSCRIBE, PUBLISH_OK or REQUEST_UPDATE. When it is non-zero, the subscriber must ACK every Normal-status, subscription-delivered object and must not FIN its request stream until the subscription ends. OBJECT_ACKmessage (provisional type 0x3184), sent on the subscription’s request stream: Group ID, Object ID, and Delta from Deadline as a new signed varint (svi64), sign-magnitude on the MOQT varint. A positive delta means early and a negative one late. Deltas ≥ the window size count as safely on time. For a player with a fixed buffer, the window is the buffer size and the delta is the playback time left when the object arrived.- It is hop-by-hop. The publisher can adjust the encoder (if it is the original publisher) or switch between existing renditions (for example under SSTS on a relay). ACKs are unilateral: they use no Request ID and get no reply. There is no coalescing, so traffic is one ACK per object.
- Open TODOs in -00: security considerations (speculative ACKs), interaction with SUBSCRIBE_TRACKS, PUBLISH_OK now carrying only EXPIRES, and a nicer signed encoding.
Relationship to other work
- Publisher-side ABR signal, complementing the subscriber-side approaches in probe tracks and fast switching, the MoQ Feedback quality-signalling draft, and the SSTS algorithms including
draft-zengin-moq-ssts-backpressure. See adaptive-bitrate. - Implementation-first. The draft documents running code in quiche moqt rather than proposing a new design.
Notes
Individual submission; not WG-adopted. Posted the day the transport-23 text was cut. See discussions-2026-11.
Links
- Datatracker: https://datatracker.ietf.org/doc/draft-vvv-moqt-object-acks/
- Announcement: moq@ietf.org, “MOQT Object ACKs” (Victor Vasiliev, 2026-11-02, permalink)