Patton electronics SmartNode Series Software Configuration Manual page 345

SmartWare Software Configuration Guide 27 • ISDN port configuration
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 inter-
faces 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 pro-
tocol 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 Mbps
transmission equipment which transports the PRI signal over copper (DSL), coax or fiber.
Introduction 343