Understanding MOQ Architecture: Publishers, Relays, and Subscribers
A deep dive into the three-tier architecture that makes MOQ uniquely suited for scalable, low-latency media delivery.
The Three Pillars of MOQ
Media over QUIC introduces a relay-based architecture that fundamentally differs from both traditional CDN-based streaming (HLS/DASH) and peer-to-peer approaches (WebRTC). Understanding this architecture is key to grasping why MOQ is generating so much excitement.
Publishers
Publishers are the sources of media content. They encode media (video, audio, or other data) and send it to one or more relays using the moq-transport protocol over QUIC or WebTransport connections.
Key characteristics of publishers:
- They organize media into tracks (e.g., separate video and audio tracks)
- Each track contains groups of objects that represent independently decodable units
- Publishers announce available tracks via a catalog
- They can publish to any relay in the network
Relays
Relays are the backbone of MOQ's scalability story. They serve a similar function to CDN edge nodes but are purpose-built for real-time media:
- Fan-out: A relay receives media from a publisher and distributes it to multiple subscribers
- Cascading: Relays can connect to other relays, forming a tree topology
- Caching: Relays can cache recent groups for late joiners
- Priority handling: QUIC stream priorities enable intelligent bandwidth allocation
The relay model means that a single publisher can reach millions of subscribers through a cascade of relays, achieving both low latency and massive scale.
Subscribers
Subscribers connect to a relay and request specific tracks. The subscription model is flexible:
- Subscribe to all objects from the latest group onward (live edge)
- Subscribe to a specific range of groups (catch-up)
- Receive catalog updates to discover available tracks
Why This Matters
This architecture solves the fundamental tension in media delivery:
| Approach | Latency | Scale | Complexity |
|---|---|---|---|
| HLS/DASH | High (3-30s) | Excellent | Low |
| WebRTC | Low (<500ms) | Poor | High |
| MOQ | Low (<500ms) | Excellent | Medium |
By using QUIC's multiplexed streams and the relay model, MOQ achieves the best of both worlds. The protocol handles congestion control, prioritization, and reliability at the transport layer, while the relay architecture provides CDN-like scalability.