Trivial Comments related to the table at:
666 Table 2.1 Control packet types
Since the table includes a column for "Direction of flow", it's redundant to include "Client" or "Server" in the Description. In addition, the descriptions are not always consistent in style.
Suggestion:
Client request to connect to Server -> Connect(ion) Request
Client subscribe request -> Subscribe Request (This actually then matches the style of the unsubscribe request)