MOQT defines all messages necessary to implement both simple publishing or
subscribing endpoints as well as highly functional Relays. Non-Relay endpoints
MAY implement only the subset of functionality required to perform necessary
tasks. For example, a limited media player could operate using only SUBSCRIBE
related messages. Limited endpoints SHOULD respond to any unsupported messages
with the appropriate NOT_SUPPORTED error code, rather than ignoring them.
Relays MUST implement all MOQT messages defined in this document, as well as processing rules described in Section 8.