There are always problems for newbies that do not know where to start for a new protocol learning.
I have been so suffered those sort of problems for a long time, after years of self studying I have found some golden rules:
1. The state machine, this is perfectly described how the protocol works.
2. The packet structure, this is perfectly described how the protocol communicates with the counterparts.
3. The roles (relationship), different roles functions differently, this described the relationship between different processes.
For any protocols, all those 3 golden rules have to be clearly understood.