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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.

A CSU/DSU is the equivalent of the modem for an entire LAN.[1]

WAN interface[edit]

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.


  1. ^ Microsoft Official Academic Course (2012). 98-366: MTA Networking Fundamentals. Hoboken, NJ: John Wiley & Sons. p. 151. ISBN 978-0-470-90183-0.