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Cable Pinouts MultiVOIP User Guide
540
ISDN Interfaces: “ST” and “U”
The MVP410ST and MVP810ST are ISDN-BRI voip units that use an S/T
outlet interface. You will need an NT1 device to connect these units to any
network equipment that has the “U” ISDN interface. In the UK, and in many
European countries, the telco supplies an NT1 device for ISDN-BRI service.
An ISDN Basic Rate (BRI) U-Loop consists of two conductors from the telco
central office to the customer premises. The equipment on both sides of the U-
loop accommodates the extensive length of the U-loop and the noisy
environment in which it may operate. At the customer premises, the U-loop is
terminated by an NT1 (network termination 1 ) device. An NT1 device makes
an end-user’s 4-wire terminal equipment compatible with the telco’s 2-wire
twisted pair ISDN-BRI line.
The NT1 drives an S/T bus. The S/T bus is usually made up of 4 wires, but in
some cases may be 6 or 8 wires.
“S” and “T” refer to connection points in the ISDN specification.
When a PBX is present, S refers to the connection between the PBX and the
terminal. (“Terminal” can mean any sort of end-user ISDN device: data
terminals, telephones, FAX machines, voip units, etc.)
Point T refers to the connection between the NT1 device and customer supplied
equipment. Terminals can connect directly to the NT1 device at point T, or
there may be a PBX (private branch exchange, i.e., a customer-owned
telephone exchange). The figure below shows “S” and “T” connection points
in an ISDN network.
Te lco
Central
Office
Point “S”
Point “T”
4-8 Wires
Point “S”
4-8 Wires
Point “U”
2 Wires
Point “S”
NT1
NT2
(PBX)
Terminal
Terminal
Terminal