Protocols have uses in inter-process communications, they allow processes to cooperate and to perform tasks as a group.
Protocols consist of:
- Ordering of messages to be exchanged,
- Message formats,
- Acions taken on the transmission and/or receipt of a message or other event.
Ordered messages with precised data formats are similar to method calls, parametrized or not.
Protocols can be modelled as a Tree, with message leading from one processes state to another, depending on data passed. Process state change can result in sending more of messages - to one or more of processes. Or messages can be sent periodically, their type, timing, amount & targets depending on state.
Source: , .
See also if You wish or need ... : Conversation State.