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Chapter 1: Understanding ISDN and the Express XL/XLT
18 Express XL/XLT User Manual 61200.070L1-1
ISDN Connection
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.
Figure 1-7
Express XL/XLT Rear Panels
PHONE 10BT
1200070L2
POWER
1200070L1
POWER
ISDN
BRI U
MAINTENANCE
10BT
ISDN
BRI U
MAINTENANCE
TO TO
NIC HUB
TO TO
NIC HUB