A wide area network(WAN)is a computer network covering multiple distance areas, which may spread across the entire world. WANs often connect multiple smaller networks, such as local area networks (LANs) or metro area networks (MANs). The world's most popular WAN is the Internet. Some segments of the Internet are also WANs in themselves. A wide area network may be privately owned or rented from servic providers, but the term usually connotes the inclusion of public (shared user) networks.

A virtual private network (VPN) riding on the public switched data network (PSDN) is often used by organizations for their private and secured communications. VPN uses encryption and other techniques to make it appear that the organisation has a dedicated network while making use of the shared infrastructure of the WAN.

WANs generally utilize different networking technologies and equipment than do LANs. Key technologies often found in WANs include SONET, Frame Relay, X.25, ATM, and PPP.

WAN technologies and protocols are mostly data link layer (layer 2) protocols which are defined by many organizations over time. The key organizations in this space are IETF for PPP, ITU-T for ATM, Frame Relay, ISO for X.25 and SONET etc.
Protocol Structure - Wide Area Network and WAN Protocols

The key WAN protocols are listed as follows:

IETF, ITU-T, ISO etc.