WANS are connected over serial lines that operate at lower speeds than LANs. Some of the WAN terms are:
1. Modems: Modems connect to public telephone circuits through dial-up.
2. CSU/DSU: Stands for Channel Service Unit / Data Service Unit. CSU/DSUs are used for connecting to Central Office of a Telephone switching company and provides serial WAN connections.
3. Multiplexors (mux): Multiplexors combine two or more signals before transmitting on a single channel. Multiplexing can be done by sharing "time" or "frequency".
4. CPE stands for Customer Premise Equipment. It is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication circuit at the demarcation point.
5. Demarc: Demarcation point between carrier equipment and CPE.
Typical WAN interfaces, that one come across frequently are:
EIA 232, EIA 449, EIA 530, V.35, and X.21. The Cisco router serial interface will be a 60-pin D-shell connector. This in turn is connected to service provider equipment, usually through a CSU/ DSU. Therefore, appropriate conversion cable need to be used when interfacing with a WAN device such a CSU/DSU. CSU/ DSU in turn is connected to the service provider through the cable supplied by the service provider.