Adtran Express XL Manual Do Utilizador

Chapter 1: Understanding ISDN and the Express XL/XLT

Express XL/XLT User Manual

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From the network, ISDN is delivered by a single 2-wire 2B1Q U-interface 
which is connected directly to the  Express XL/XLT.  ISDN network termina-
tion is designed into the Express XL/XLT, eliminating the need and expense 
of a separate NT1.  For network testing, the Express XL/XLT responds to NT1 
test commands from the telephone company central office (CO).

The Express XL/XLT has one RJ-45 jack, labeled ISDN BRI U on the rear panel 
for network connection (see Figure 1-7).  ISDN basic rate service divides a stan-
dard telephone line into three digital channels capable of simultaneous voice 
and data transmission.  The three channels are comprised of two bearer (B) 
channels at 64 kbps and one data (D) channel at 16 kbps, known as 2B+D.  

The  Express XL/XLT also supports a leased digital connection allowing data 
to be transferred at up to 144 kbps over a 2-wire facility using the same RJ-45 
jack.  This type of service is a permanent connection between endpoints and is 
sometimes referred to as a leased connection, a dedicated connection, a nailed-
up connection, or a private circuit.  Leased connection or leased line is used in 
this manual to represent these types of services. 

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