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MultiVOIP User Guide Cable Pinouts
357
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)
Ter mina l
Terminal
Terminal