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Common ISDN Problems
435
S reference point The S reference point is the interface between the
ISDN router (or other user equipment) and the NT2 or NT1. Note that
the user equipment is referred to as the TE1 or TA.
T reference point The interface between the NT1, or the local loop ter-
mination point, and the NT2, or customer site switching equipment, is
referred to as the T reference point. This point, along with the S reference
point, is within the customer premises, and faulty wiring may be the cause
of a problem within this context.
U reference point The U reference point is between the NT1 and the
LE. It is normally serviced on a single pair to reduce costs and simplify
installations.
Layer 1 S/T Interface This connection uses a physical connector of RJ-45,
as defined in ISO 8877. A straight-through pin configuration connects the
terminal end point (TE) to the network termination (NT). Table 8.2 reflects
the specific pinning.
T A B L E 8 . 2
The RJ-45 ISDN S/T Interface
Pin
Terminal End-Point (TE)
Network Termination (NT)
1
Power +
Power +
2
Power -
Power -
3
Transmit +
Receive +
4
Receive +
Transmit +
5
Receive -
Transmit -
6
Transmit -
Receive -
7
Power -
Power -
8
Power +
Power +
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