1. 
   CSU-DSU
   channel service unit/digital service unit
   Found op http://foldoc.org/CSU-DSU
   
   
2. 
   CSU/DSU
   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 telec...
   Found op http://en.wikipedia.org/wiki/CSU/DSU
   
   

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