Design Space Analysis of MoQ

Design Choice 1: Static Tree Topology versus Dynamic Mesh Topology

• Static Tree Topology

  

  • In traditional CDN network, each CDN site can be viewed as a relay. The media need to first go up to the root of the tree, then go down to another leaf node, traversing multiple (at least 3) relays if the CDN hierarchy is deep or the producer and the consumer is highly distributed.
  • [QUICR-arch] is similar to the tree topology of CDN with one improvement: the relay can shortcut the media transmission. If the producer and the consumer share a parent relay, the media will be forwarded in the relay instead of the root of the tree (called Origin in QUICR's term).

• Dynamic Mesh Topology

  

  • Another approach is to connect the relays in a dynamic mesh instead of a static hierarchy. Alibaba's low-latency live streaming network builds on a flat CDN overlay [LiveNet].
  • A centralized controller collects the latency between each relay periodically and calculates the optimal path (latency-wise) for each media stream dynamically. P - Relay 1 - Relay 4 - C, if there’s no congestion control between Relay 1 and Relay 4. If there’s, then P - Relay 1 - Relay2/3 - Relay 4 - C.

Design Choice 2: QUIC hop-by-hop versus end-to-end

1. Run the entire MoQ protocol inside QUIC encryption, including the media metadata which is needed by relay (see Figure 3). Thus the relay has to terminate the QUIC connection, decrypting the QUIC payload. This will require each relay node hold a valid CA certificate and run the CA verification process. Just like what the CDN node does nowadays.

1. Only encrypt the media content using QUIC encryption but leave the metadata to other mechanism (see Figure 4). In this way, the QUIC connection is from producer to consumer. The relay does not need to decrypt the QUIC, saving the computing power.