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Media over QUIC Transport (MOQT)

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draft-ietf-moq-transport-19 | published 2026-07-06 | Datatracker draft-ietf-moq-transport-18 | published 2026-05-12

Authors

Abstract

MOQT is a publish/subscribe protocol that runs over QUIC and WebTransport. It leverages transport capabilities including streams, datagrams, priorities, and partial reliability. MOQT enables content delivery both directly between endpoints and through intermediate relays, achieving scalable low-latency distribution. Despite its name referencing media, the specification emphasizes that MOQT remains content-agnostic and applicable across various use cases (abstract reframing in draft-18 — see discussions-2026-05 for Will Law’s parallel May 12 recharter proposal).

Key Concepts

  • publish-subscribe: Core messaging pattern - PUBLISH, SUBSCRIBE, FETCH, REQUEST_OK/REQUEST_ERROR, PUBLISH_DONE
  • subgroups-and-objects: Data hierarchy: Track > Group > Subgroup > Object
  • relays: First-class relay support for CDN-style distribution
  • track-properties: Metadata attached to tracks and objects via Key-Value Pairs
  • joining-fetch: Mechanism to fetch historical data when joining a live session
  • qmux: TCP fallback via QUIC multiplexing over TLS+TCP
  • URI Scheme: moqt:// URI scheme with fragment identifier support (PR #1571)

Version history

draft-19 (published 2026-07-06)

Cut at the interim-2026-moq-18 (approved by Ian Swett); primarily an editorial clarification and validation-rule pass — the product of the post-draft-18 issue read-through and phased Design-PR review, with no major new wire mechanisms. Changes since draft-18:

  • FIRST_OBJECT bit clarified to indicate the first object ever published in that subgroup.
  • Malformed-Track conditions extended with explicit Object-ID-ordering checks within Groups.
  • Property-handling rules clarified for relay forwarding of unknown properties.
  • Location Filter behavior specified for when no content has been delivered yet.
  • Session-termination error codes expanded for more protocol-violation scenarios.
  • Track Namespace field constraints / validation rules documented.
  • Subscription-state destruction timing clarified.

draft-18 (published 2026-05-12)

Key wire/spec changes from draft-17:

  • Remove Required Request ID (PR #1615, materialises the Apr 27 interim consensus) — Required Request IDs are removed; Request IDs remain for individual requests (used by Joining FETCH and GOAWAY).
  • Add FIRST_OBJECT bit to SUBGROUP_HEADER type (PR #1618) — bit 6 (0x40) signals the subgroup contains the first object published by the original publisher; type byte expands 0b00X1XXXX → 0b0XX1XXXX (still 1-byte varint).
  • Forbid relays from lying about LARGEST_OBJECT (PR #1621).
  • Split DELIVERY_TIMEOUT into two timeouts (PR #1605) — OBJECT_DELIVERY_TIMEOUT (a more precise replacement for DELIVERY_TIMEOUT) plus a new SUBGROUP_DELIVERY_TIMEOUT (covers subgroups fully queued but not fully delivered). Closes the “DELIVERY_TIMEOUT is unimplementable” issue.
  • Improve Startup Latency and 0-RTT (PR #1544) — new sections on reducing startup latency / 0-RTT flow with WebTransport.
  • Per-request GOAWAY (PR #1617) — GOAWAY on request streams migrates individual requests; a zero-length URI causes the endpoint to re-issue the request on the specified URI session.
  • Improve Security Considerations (PR #1625) — rebases and extends magnus-westerlund’s long-parked PR #1455.
  • Clarify definition of scope (PR #1629).
  • Abstract reframed to emphasise that MOQT is content-agnostic despite the “media” name.

draft-17 (published 2026-03-02)

Significant changes from draft-16:

  • Unidirectional control streams for 0-RTT subscribe capability
  • SUBSCRIBE_NAMESPACE split into two messages: SUBSCRIBE_NAMESPACE (namespace info) and SUBSCRIBE_TRACKS (PUBLISH notifications)
  • Subscription filters moved to be a Param (PR #1590)
  • Track Properties added to REQUEST_OK (PR #1576)
  • Allow 7-byte varint and non-minimal encodings (PR #1595)
  • Editorial: consistent use of “MOQT” for protocol references (PR #1597); “message” instead of “frame” (PR #1587)

Recent Highlights

Day-by-day WG/PR activity lives in the wiki log; this section keeps only durable milestones.

  • Fast first-impl turnaround for draft-18: within ~6 days of the May 12 publication, three distinct codebases had shipped it (moq, imquic, mondain/moqxr) — the fastest spec → first-impl turnaround the wiki has tracked.
  • London interim (June 11–12, interim-08/interim-10) confirmed several directions: keep the object-ID filter; fill-fetch replaces joining-fetch; SWITCH_FROM hard mode; remove Request ID from GOAWAY; PUBLISH_DONE precedes FIN on response streams; track properties stay immutable (priority updates via the data plane); draft-18 is the Vienna interop target.
  • DTS/SWITCH consensus (June 11): base-spec integration lacked rough consensus, so Dynamic Track Switching is adopted as a separate WG extension, draft-ietf-moq-dts4moq (Will Law), with the door left open to later merge into MOQT. See switch-abr.
  • June 22 interim (interim-17) renamed DTS → Sender-Side Track Switching (SSTS), made the switching algorithm an extensible IANA-registered numeric ID with a mandatory “Algorithm Zero”, and removed the per-set DDoS-protection negotiation properties (rely on auth tokens + existing relay protections). See interim-meetings.
  • draft-19 published (2026-07-06): an editorial clarification pass following Cullen Jennings’s ~59-issue read-through of draft-18 (June 15); issues were converted into PRs under a phased review, with “Design” PRs needing two weeks open + four-editor stamps to make the July-6 cut.
  • IANA early review of draft-19 (2026-07-16): IANA (Amanda Baber, ticket #1456083) reviewed the draft ahead of IETF 126 and returned a pre-Last-Call punch-list — the IANA Considerations section is incomplete; the new registries need a named group (“Media over QUIC Transport”), RFC 8126 designated-expert guidance, protocol-differentiated names, and explicit numeric bounds; and the allocations must be reconciled against inconsistent/duplicate registry values requested by loc, secure-objects, and msf. This was one of five reviews Baber filed the same morning — companion early reviews landed for loc-03 (#1456079), msf-01 (#1456080), privacy-pass-auth-03 (#1456081), and secure-objects-01 (#1456082), all flagging the same defect class (registry name/reference mismatches vs the registries transport-19 establishes + missing RFC 8126 boilerplate) — i.e. IANA’s cross-document verdict on the whole MoQ set. Tracked in issue #1814 (afrind); the msf side is msf #191 (Will Law), with Will Law’s cleanup PRs msf #192–#195 opened July 17. Reframes the “Path to WGLC” work as enumerated registry/IANA items rather than open protocol design.
  • WGLC-prep security/editorial cluster (2026-07-21): during IETF 126 week the editors merged a six-PR hardening pass on the editor’s copy — no new published revision (transport-19 stands) — closing security-considerations and registry-hygiene gaps: impersonation-prevention detail (#1789, Suhas), moqt:// URI-scheme security per RFC 7595 §3.7 (#1772), a hex-enumeration→bitfield code-point syntax rewrite (#1774), expanded mutual-TLS security considerations (#1786, afrind), a REDIRECT retry-interval-0 clarification (#1785), and FORWARD on a REQUEST_UPDATE for SUBSCRIBE_TRACKS (#1812, sharmafb).
  • IETF-126 Monday session — chairs shape the Path to WGLC by trimming the core (2026-07-20; minutes posted 2026-07-22, revised to -01 and formally circulated for WG review by Magnus Westerlund on 2026-07-29 with corrections due ~Aug 12): this Monday-slot document is the only IETF-126 MOQ minutes doc — the Thursday (July 23) and Friday (July 24) sessions ran but were never separately minuted. The WG’s headline decisions were about scope reduction to reach Last Call, not new design. (1) Chairs called consensus to move range filters and Sender-Side Track Switching (SSTS) into separate drafts, out of the core transport document — Cullen Jennings formally objected, citing a roughly 50/50 room split, and the Area Director affirmed the chairs’ right to call consensus (a contested but standing determination). (2) Management, metrics, and diagnostics considerations spun off into a new applicability/manageability document in its own repo — Alperen Temel volunteered to write the initial diagnostics/relay-management draft. (3) The chairs framed transport stabilization as the critical blocker — “if transport does not ship, none of the other WG drafts can progress” — with secure-objects queued for WGLC once the shared IANA registries settle. Editorial WGLC-prep also continued on the editor’s copy: afrind opened #1824 (REDIRECT empty-namespace/name ambiguity), #1823 (security consideration for logging untrusted string fields), and #1822 (Timed-Out gap status for expired Fill Timeout) on July 22, and Suhas opened #1825 (replace the FORWARD parameter with Range-Filter-based pausing). afrind’s 1822 all merged July 30 — the most editor’s-copy content movement since the pre-Vienna push — alongside a new #1817 (define host resolution for moqt:// URIs, tightening the URI semantics michalhosna’s issue #1835 reopened) and Mathis Engelbart’s one-line #1836 (CLIENT_SETUP→SETUP naming fix); Suhas’s #1825 stays OPEN. transport-19 stands.
  • First draft-20-bound merges land (2026-08-13): after the Aug-10 virtual interim (interim-2026-moq-21) walked the core-transport PR set discussion-only, the editors landed the first batch toward draft-20 on the editor’s copy — the Location Filter redesigned to match the design of the other filters (#1809, Mo Zanaty), the new PUBLISH_STATE_NOTIFY strictly-informative control message (#1820, afrind), a “recommend Secure Objects for confidentiality from relays” security note (#1755, afrind — closes issue #1711), and a “first byte of object” fix for payload-less objects (#1844, sharmafb — closes issue #1841). No new revision published — transport-19 still stands on the datatracker; the remaining filter/fetch/switch redesign PRs (#1673/#1674/#1825/#1834 + Suhas’s #1851–#1853 batch) stay OPEN. The interim-2026-moq-21 minutes (posted 2026-08-14) frame this as the start of an editorial cadence: draft-20 = a purely-editorial cut just before the editorial meeting; draft-21 = the editorial meeting’s output; draft-22 = the next official interop target. The minutes also recorded a lean toward rejecting the updatable-default-publisher-priority PR #1770 (“error-prone … probably not needed”) and consensus that the URI query component is out of MoQT scope — producing afrind’s PR #1855 (“Exclude URI query component from MOQT scope,” Fixes #1835), while Will Law’s FETCH-pacing proposal (fetch_pacing_supported + logarithmic pacing_rate) continues as an external extension.
  • Consensus call on the draft-18 content closed (opened 2026-07-06, concluded 2026-07-24): co-chair Martin Duke ran a formal consensus call on the draft-17 → draft-18 diff, asking the WG to file any resulting issues “no later than 20 July” with “subsequent objections [facing] a higher bar.” He closed it out on-list July 24 14:14 UTC — “This concludes the consensus call on draft-18. Any issues with the -17/-18 diff should be in Github by now.” — formally settling the -18 baseline as the WG works the Path to WGLC. (This on-list thread was mistakenly dismissed as a fetch artifact in two prior wiki updates; it is verifiably real — message, corrected here.)
  • MOQT-over-QMux ruled out of the WG’s current charter (chairs + AD, June 17): the TLS+TCP fallback proceeds as an individual draft until a recharter, scoping the QMux-framing work out of the transport draft. See qmux.
  • AUTH design team (formed June 12) produced the WG’s first new draft since transport-18 — [[moq-c4m|draft-ietf-moq-c4m-01]] (Common Access Token authorization).

Open design questions

Substantive topics still being worked as this page is written:

  • Fill-fetch vs Joining FETCH: whether to replace Joining FETCH with unidirectional fill-fetch streams (PR #1673, revising Subscription-Fill #1642) — Cullen Jennings would keep Joining FETCH pending operational experience, and flags error-delivery, duplicate-object, and nested-FILL_PARAMETERS concerns. See joining-fetch.
  • SSTS (Sender-Side Track Switching): the “Algorithm Zero + IANA registry” extension design (PR #1638), meant to be validated by more than one algorithm before draft-19. At IETF 126 (July 20) the chairs called consensus to move SSTS into a separate draft, out of core transport (contested by Cullen Jennings; AD affirmed the chairs) — so it is now slated to leave the transport document. See switch-abr.
  • Range filters: re-adding location-based subscription filters (Mo Zanaty’s PR #1765). Slated to move into a separate draft per the contested IETF-126 consensus call — the least-wanted part of the draft-18→19 delta (Luke Curley won’t implement them; imquic ignores the property filters). In the interim, Mo Zanaty’s Location-Filter redesign to match the other filters’ shape merged Aug-13 (#1809, toward draft-20), while Suhas’s #1825 (July 22) — replacing the FORWARD parameter with Range-Filter-based pausing — stays OPEN.
  • Top Tracks Filter × SSTS/ABR interaction: how the Top-Tracks-Filter (PR #1830) actually combines with SSTS (or any ABR algorithm) is unresolved. Ian Swett’s July-27 list thread “Top Tracks and SSTS (or ABR in general)” (permalink) argues ABR is essential for the video-conferencing use case and asks four concrete mechanism questions the current design doesn’t answer: how to send the initial SUBSCRIBE_TRACKS (a Track-Property-Filter for the ideal resolution combined with Top Tracks?), how the focal viewport gets higher priority when deciding which feed to downswitch, how a client-pinned non-default feed is prioritized, and whether any demo (even simulated) shows the two working together. He notes Google Meet’s production solution is “sufficiently complex I can’t summarize it” and doubts MoQ will match it soon. Two implementers replied July 28 with a converging “discovery then selection” model: Yu You (Nokia) framed it as a two-step pipeline — the Top-N filter answers “what” (evaluate a namespace’s tracks by property value, promote the N highest, publisher subscribes upstream to all N) and SSTS answers “how” (apply the switching algorithm, e.g. a bandwidth threshold, to forward exactly one; the relay holds upstream to all N alternatives but sets downstream forwarding to 0 for the unselected, giving “Top-1 delivery” without overdelivery/congestion, and a demoted track leaves the switching set). Will Law (Akamai) cast Top Tracks as a discovery mechanism like SUBSCRIBE_NAMESPACE (clients assign the resulting tracks to switching sets via a SWITCHING_SET_ASSIGNMENT parameter on PUBLISH_OK), argued SSTS entry will lean on SUBSCRIBE_NAMESPACE + plain SUBSCRIBE more than dynamic Top-Tracks selection, and floated unifying the two as one filter framework — rename Top Tracks to TRACK-FILTERS, make SSTS parameters (rank, weight, throughput threshold) reserved track properties, and add a flag to “apply SSTS to the filtered tracks.” Still open; Swett’s demo-existence question (does any Top-Tracks + SSTS demo exist?) is unanswered.
  • Subgroup-start signalling: draft-18 shipped the FIRST_OBJECT bit (PR #1618), but the list debated alternatives (Subgroup ID == first Object ID; Luke Curley’s per-subgroup counter for cache-gap detection).
  • Compression layering: whether compression belongs at the transport, MSF/streaming-format, or Full-Track-Name layer, and hop-by-hop vs end-to-end semantics. See moq-dev.
  • 7-byte varint / non-minimal encodings: allowed since draft-17 (PR #1595), but flagged as a footgun in the draft-19 read-through.
  • PUBLISH_STATE_NOTIFY (formerly proposed as SUBSCRIPTION_STATE_UPDATE / PUBLISH_NOTIFY): afrind’s new strictly-informative control message to notify subscription state — PR #1820 MERGED 2026-08-13 into the editor’s copy (toward draft-20). Still open is the related question issue #1821 (Otto Hermann): what a subscriber is entitled to observe after an Object becomes unavailable — both touch draft-19’s clarified subscription-state destruction timing.
  • FETCH and REQUEST_ERROR encoding: Mathis Engelbart’s issue #1837 (July 31) raises an encoding question on FETCH and REQUEST_ERROR — a fresh WGLC-hygiene item on the editor’s copy (no PR yet).

ALPN Negotiation

MOQT negotiates the draft revision via the QUIC/WebTransport ALPN. Each revision maps to moqt-NN with wire version 0xff0000NN; the QUIC-multiplexed (qmux) transport prefixes the same token as qmux-00.moqt-NN. (The final RFC will use the bare moqt token.)

  • moqt-19 — draft-19 (0xff000013), the current published revision
  • moqt-18 — draft-18 (0xff000012); the Vienna interop target
  • moqt-17 — draft-17 (0xff000011)
  • moqt-16 — draft-16 (0xff000010)
  • moq-00 — draft-14 (legacy); the bare qmux-00 token (no suffix) likewise implies draft-14

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