In information technology, a protocol is the special set of rules that end points in a telecommunication connection use when they communicate. Protocols exist at several levels in a telecommunication connection. There are hardware telephone protocols. There are protocols between each of several functional layers and the corresponding layers at the other end of a communication. Both end points must recognize and observe a protocol. Protocols are often described in an industry or international standard.

Common Layer 3 protocols in the OSI model used today are:

• AppleTalk
• IP
• IPX
• SPX

Common Layer 4 protocols in the OSI model used today are:

• UDP
• NetBIOS
• NetBEUI
• TCP

On the Internet, there are the TCP/IP protocols, consisting of:

• Transmission Control Protocol (TCP), which uses a set of rules to exchange messages with other Internet points at the information packet level.
• Internet Protocol (IP), which uses a set of rules to send and receive messages at the Internet address level.
• Additional protocols that are usually packaged with TCP/IP, including the Hypertext Transfer Protocol (HTTP) and File Transfer Protocol (FTP), each with defined sets of rules to use with corresponding programs elsewhere on the Internet.