Protocols are sets of standards that networks must follow for proper functioning. Protocols are implemented in hardware or software. The International Standards Organization (ISO) has developed a model for network protocol design. This model is called the Open Systems Interconnection (OSI) model. Examples of LAN protocols are Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI). Examples of MAN protocols are E lines, Distributed Queue Dual Bus (DQDB), and Switched Multimegabit Data Services (SMDS). Examples of WAN protocols are Integrated Services Digital Network (ISDN), frame relay, Asynchronous Transfer Mode (ATM), and Synchronous Digital Hierarchy (SDH).
