What does an application layer protocol specify?

Show Answers

The categories of messages communicatedThe structure, syntax, and meaning of messagesGuidelines on the timing and manner of sending and receiving messagesAll of the above

Explanation

An application layer protocol encompasses the types of messages exchanged (A), the format, syntax, and semantics of these messages (B), as well as the rules governing when and how processes send and respond to messages (C), making option D the correct choice.