If the subscriber is aware of a namespace of interest, it can send SUBSCRIBE_NAMESPACE to publishers/relays it has established a session with. The recipient of this message will send any relevant ANNOUNCE, UNANNOUNCE or PUBLISH messages for that namespace, or more specific part of that namespace.
A publisher MUST send exactly one SUBSCRIBE_NAMESPACE_OK or SUBSCRIBE_NAMESPACE_ERROR in response to a SUBSCRIBE_NAMESPACE. The subscriber SHOULD close the session with a protocol error if it detects receiving more than one.
The receiver of a SUBSCRIBE_NAMESPACE_OK or SUBSCRIBE_NAMESPACE_ERROR ought to forward the result to the application, so the application can decide which other publishers to contact, if any.
An UNSUBSCRIBE_NAMESPACE withdraws a previous SUBSCRIBE_NAMESPACE. It does not prohibit original publishers from sending further ANNOUNCE or PUBLISH messages, but relays MUST NOT send any further PUBLISH messages to a client without knowing the client is interested in and authorized to receive the content.