A CSU/DSU (Channel Service Unit/Data Service Unit) is a digital-interface device used to connect data terminal equipment (DTE), such as a router, to a digital circuit, such as a Digital Signal 1 (DS1) T1 line. The CSU/DSU implements two different functions. The channel service unit (CSU) is responsible for the connection to the telecommunication network, while the data service unit (DSU) is responsible for managing the interface with the DTE.
DSL and cable modems are CSU/DSUs because they convert from one type of digital signal to another. A CSU/DSU is the equivalent of the modem for an entire LAN.
Video CSU/DSU
WAN interface
The WAN Interface Card (WIC) may contain an integrated CSU/DSU that can be inserted into a router slot. An example of a WIC is the 1-port 56/64-kbit/s DSU/CSU WIC (WIC-1DSU-56K4) by Cisco Systems.
Maps CSU/DSU
References
Source of article : Wikipedia