Issue 2 - 07/00 A3-7
Appendix 3—Introduction to ISDN
Basic Rate power
Power is provided across the network so that, in the event of a
mains failure, a basic telephone service is still provided.
Primary Rate
There are two variations of the Primary Rate Interface. In
Europe, primary rate comprises of 30 B channels and one D
channel, known collectively as 30B+D. In the U.S., the
primary rate standard comprises of 23 B channels and one D
channel, known collectively as 23B+D.
B Channels
The B channels contain user data at rates of up to 64kbps.
D Channel
The D channel is reserved for control and signalling data at
64kbps.
Primary Rate access to the ISDN
The Primary Rate Interface is point-to-point only; the
connection is simply between the network and a PABX or
similar piece of equipment. The line carrying the traffic is
either a 75 Ohm co-axial, a 120 Ohm twisted pair or a fibre
optic cable.
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