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Chapter 1. Understanding ISDN and the Express 4110/4120
1-16 Express 4110/4120 User Manual 61200176L3-1
Rear Panel
The Express 4110/4120 has one RJ-49C jack, labeled ISDN, on the rear
panel for network connection (see Figure 1-13 on page 1-17 and Figure 1-
14 on page 1-17). The OFF/ON switch block is for factory default and
firmware downloading. With switch 1 in the up or OFF position, the
Express 4110/4120 will go immediately into a download mode when
power is enabled. Switch 1 must be in the down or ON postition in order
to boot up normally. Switch 2 in the up or OFF position will force the
entire configuration to be factory defaulted.
ISDN Connection
From the network, ISDN is delivered by a single 2-wire 2B1Q U-interface
which is connected directly to the Express 4110/4120. ISDN network ter-
mination is designed into the Express 4110/4120, eliminating the need
and expense of a separate NT1. For network testing, the Express 4110/
4120 responds to NT1 test commands from the telephone company cen-
tral office (CO).
The Express 4110/4120 has one RJ-49C jack, labeled ISDN, on the rear
panel for network connection (see Figure 1-13 on page 1-17 and Figure 1-
14 on page 1-17). ISDN basic rate service divides a standard telephone
line into three digital channels capable of simultaneous voice and data
transmission. The three channels are comprised of two bearer (B) chan-
nels at 64 kbps and one data (D) channel at 16 kbps, known as 2B+D.
The Express 4110/4120 also supports a leased digital connection allowing
data to be transferred at up to 128 kbps over a 2-wire facility using the
same RJ-49C jack. This type of service is a permanent connection between
endpoints and is sometimes referred to as a leased connection, a dedi-
cated connection, a nailed-up connection, or a private circuit. Leased con-
nection or leased line is used in this manual to represent these types of
services.