Large networks such as those that cover complete country or state are called 'wide area network' (WAN). In large, complex environments, the number of users and devices on a network can grow into the thousands and beyond. Long distance telephone systems are wide area networks. Cables of various types are used for interconnection. Radio links using microwave relay stations or satellites are also used. Mostly telephone networks are used for voice communication, but if modems are used, digital data can be transmitted over the telephone network. Internet is a WAN internetwork that includes large number of machines and millions of users worldwide.

In WAN short circuit errors, noise errors, atmospheric error are higher than any other type of networks. But most advance technologies of data transfer are used to minimize the error.