MB> Wes Newell wrote in a message to Radek Stachowiak:
 WN> CSU/DSU- Channel Service Unit/Data SU. Most commonly used
 WN> with ISDN's. 
 MB> ISDN uses a Network Terminator, of which there are 
 MB> various types.  An NT-1, for example, is a basic 
 MB> electrical interface.  An NT-2 is practically a PBX.
 MB> CSU/DSU equipment is used on leased lines, which are 
 MB> generally unswitched.  There are two basic types in 
 MB> common use, one to connect to the four-wire ingress 
 MB> used with T1 and the other to connect to the two-wire 
 MB> ingress used with 56 kbps.
Not to be picky, but a T1 circuit falls under ISDN as a PRI (Primary Rate 
Interface), Just as a BRI (Basic Rate Interface) falls under ISDN. ISDN is 
not limited to just the BRI.
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