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A CSU/DSU (Channel Service Unit/Data Service Unit) is a digital-interface device used to connect a Data Terminal Equipment device or DTE, such as a router, to a digital circuit, such as a T1 line. The CSU/DSU implements two different functions. The CSU is responsible for the connection to the telecom network while the DSU is responsible for handling the interface with the DTE. A CSU/DSU is the equivalent of the modem for an entire LAN.[1]

WIC (WAN Interface Card)[edit]

The WIC (WAN Interface Card) 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) from 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.