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Sonata
Hand Held ISDN Tester—User Guide
A2-6 427869
Basic Rate
Basic Rate (BRI) consists of two B channels and one D
channel, known collectively as 2B+D.
Basic Rate access to the ISDN
The diagram below illustrates Basic Rate ISDN operation.
In this illustration, a 4 wire bus consisting of a transmit and
receive pair (known as the ‘S bus’), is connected to the NT1.
The S bus is terminated at the NT1 and the distant end, on
both the transmit and receive pairs. Connection to the bus is
usually made via 8-pin plugs which conform to ISO
Specification 8877. Over this bus pass the 2B+D channels.
Point-to-point and point-to-multipoint links
The S bus can operate in either point-to-point (PP) or point-
to-multipoint (PMP) mode.
• On a PP link, one TE is connected at the end of up
to 1km of cable.
• On a PMP link, up to 8 terminals can be connected
in parallel along the bus. The length of the bus is
limited to about 200m, depending on the cable.
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