• data compression method, if any

• how the receiving device will indicate that it has received a message

There are a variety of standard protocols from which programmers can choose. Each has particular advantages and disadvantages; for example, some are simpler than others, some are more reliable, and some are faster.

From a user's point of view, the only interesting aspect about protocols is that your computer or device must support the right ones if you want to communicate with other computers. The protocol can be implemented either in hardware or in software.

Protocol Directory 
Site contains information on all known networking protocols from ATM to IPX and TCP/IP. Well laid-out with HTML and PDF versions of protocol information.

Yahoo!'s Internet Protocols Page
Yahoo!'s directory of Internet protocols.

Protocol Dictionary
Information on all network protocols, including a precise overview of the protocol, a detailed protocol format, related protocols and reference links.