Syntax: Syntax relates to the structure or format of the data, meaning the order in which they are presented. For example; a simple protocol may expect the first 8 bits of data to be the address of the sender, the second 8 bits to be the address of receiver, and the rest of the stream to be the message itself.
Semantics: Semantics relates to the meaning of each section of bits. How is a specified pattern to be interpreted; and what action is to be taken based on that interpretation? For instance does an address identify the route to be taken or the final destination of the message?
Timing: Timing refers to two vital characteristics: when data should be sent and how fast they can be sent. For example if a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload the receiver and data will be largely lost.