Wide-area networks (WANs) are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations. Typically, a WAN consists of two or more local-area networks (LANs).
Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. A WAN connects computers at two sites in different regions or even different countries by transmitting data over a ``point-to-point'' link. A link is usually established over analog or digital telephone lines and, for worldwide connections, data may be relayed via communications satellites. A point-to-point link can also be established over a dedicated serial line if the hardware at each end is capable of maintaining sufficient signal strength over the distance between the systems.
Analog transmission requires the use of a modem to convert or ``modulate'' digital data into an analog audio form so it can be sent over a telephone line, and another modem at the receiving end to convert or ``demodulate'' the analog signal back into digital data. The bandwidth of an analog telephone line is usually 3000Hz (3000 cycles per second) but sophisticated encoding and compression techniques allow the transmission of data at up to 56.6kbps over suitably noise-free lines.
Digital transmission over ISDN (integrated services digital network) lines uses ...
The general type of WAN connections and network hardware that are used to interconnect offices are described.