A client creates a subscription on a given channel. Remember, there is no support for wildcards, so a subscription is really tied to one and only one channel. The server will maintain the subscription state on behalf of the client until the latter closes the subscription (or its connection).
If there are messages in the log for this channel, messages will be sent to the consumer when the subscription is created. The server will send up to the maximum number of inflight messages as given by the client when creating the subscription.
When receiving ACKs from the consumer, the server will then deliver more messages, if more are available.
A subscription can be created to start at any point in the message log, either by message sequence, or by time.
The following pages describe all of the types of subscriptions.