QMux - QUIC Multiplexing over TCP

A fallback transport mechanism for moq-transport when UDP/QUIC is unavailable.

Problem

Some environments block UDP traffic (corporate networks, certain mobile networks), making QUIC unavailable. Safari also lacks WebTransport support, requiring an alternative.

Solution

QMux provides QUIC-like multiplexing over TLS+TCP, enabling MOQT to work over TCP connections. luke-curley uses QMux for Safari support.

ALPN Negotiation

QMux versions are indicated in the ALPN string:

• qmux-00.moqt-17 - QMux version 0, MOQT draft-17
• qmux-00.moqt-16 - QMux version 0, MOQT draft-16
• qmux-00 alone implies draft-14 (legacy, technically incorrect)

When qmux-01 comes out, it would double the ALPN permutations. Luke’s qmux library automatically adds/strips the prefix for supported versions.

Design Discussion

alan-frindell (2026-03-15): “I sort of think the right answer is to use moqt-16, and define that TLS+TCP moqt-16 ⇒ qmux-00” - generated 19 replies.

Deployment

• Meta’s moxygen relay at fb.mvfst.net:9449 supports both QMux TLS/TCP and QUIC
• WebSocket proxy available at wss://fb.mvfst.net:9450 proxying to TLS on port 9449

Related

• moq-transport - Main protocol
• interop-endpoints - Relay endpoints supporting QMux