ISDN Port Configuration
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Figure 24-1: ISDN Reference Points
The S reference point is on the subscriber interface. This is the typical 4-wire connection between an
ISDN phone and an ISDN PBX. Be aware that many ISDN PBX vendors use non-standard
proprietary 2-wire interfaces to connect the Terminals to the PBX.
The T reference point is on the trunk interface of a PBX. This is the standard 4-wire interface between
the PBX and the network termination unit (NTU) also known as NT1 in standard terminology. The
ISDN layer 2 protocol at this point is in point-to-point mode between the NTU and the PBX.
The 4-wire layer 1 specification S and T interfaces is foreseen for in-house installations and carries a
maximum of 150 meters.
The S/T reference point is on a point-to-multipoint S-Bus. Here several terminals are connected
directly to the same BRI NTU. The S and T reference points are “collapsed”. The NT2 is not
represented by any equipment unit.
The U reference point is on the transmission side of the NTU designed to carry the ISDN line over
the last mile. For basic rate interfaces this is typically a DSL technology working on legacy copper
pairs over a distance up to 12 kilometers. For primary rate lines, DSL, coax and fiber transmission is
in use. In most European countries the U interface is not accessible to the subscriber, the operator
always provides the NT1. In the US and some other countries the NT1 can be integrated into the
NT2, i.e. the PBX is connected directly to the U interface.
The V reference point is typically a y-wire interface between the line card of the public switch and
the 2 Mbit/s transmission equipment, which transports the PRI, signal over cooper (DSL), coax or
fibre.
24.1.2 Possible SmartNode Port Configurations
The SmartNode ISDN ports can be configured for connection to S, T, S/T and V interfaces. Refer to
Figure 24-2, which illustrates some of the possible network integration options.
Software Configuration Guide, Revision 1.03
Summary of Contents for SmartWare R2.00
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