Isdn connection – ADTRAN L128 User Manual
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Chapter 1: Understanding ISDN and the Express L128/L128T
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Express L128/L128T User Manual
61202.070L1-1
ISDN Connection
From the network, ISDN is delivered by a single 2-wire 2B1Q U-interface
which is connected directly to the Express L128/L128T. ISDN network termi-
nation is designed into the Express L128/L128T, eliminating the need and ex-
pense of a separate NT1. For network testing, the Express L128/L128T
responds to NT1 test commands from the telephone company central office
(CO).
The Express L128/L128T has one RJ-45 jack, labeled ISDN, 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 L128/L128T 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 L128/L128T Rear Panel
1
O
ISDN
OFF
ON
2
1
EIA232
10 BASE T
POWER
1
2
3
4
TO
HUB
TO
NIC
1
O
ISDN
OFF
ON
EIA232
10 BASE T
POWER
1
2
3
4
TO
HUB
TO
NIC
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