Matrix Telecom SIMADO GBR42 System Manual page 93

Matrix
S/T reference point.
U-The reference point between NT1 devices and line-terminations
equipment in the local exchange. The U reference point is relevant
only in North America, where the NT1 function is not provided by the
local exchange. In other countries, the ISDN service providers provide
NT1 along with the services i.e. the U-interface is built in feature of
the service. The customer gets S/T interface.
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SIMADO GBR42 V1 System Manual 93