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At your site, the BRI line takes the form of an RJ45 or RJ11 wall jack,
which in ISDN is called the U interface. RJ45 connectors have eight pins
and RJ11s have four or six pins. At the U-interface, you can plug an RJ11
connector into an RJ45 jack, and your line will work correctly.
The telephone company adds a line termination device at their end of the
BRI that adapts the line for ISDN.
B-channels and D-channels
Though BRI signals are transmitted over an ordinary pair of wires, BRI
typically contains three channels. The channels are created by complex
signaling techniques.
BRI is composed of two 64-kbps B-channels and one 16-kbps D-channel:
This
B-channels
D-channel
Physical View
Figure 2.5 ISDN BRI—Three Logical Channels Over One Pair of
The I-modem and ISDN
Does this
Carries (or "Bears") data or voice traffic
Sets up and tears down calls
Logical View
RJ45 Connector
Wires.
D-channel
D-channel
D-channel (16 Kbps)
B-channel (64 Kbps)
B-channel (64 Kbps)
2-3
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