Appendix C: A Brief ISDN Glossary
ISDN PC Card – 17 Appendix C: A Brief ISDN Glossary
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Supplementary
Services
Additional ISDN capabilities that are only avail-
able in Euro ISDN. Some of them are standard
convenience features, others are only are avail-
able upon request. Supplementary Services in-
clude Calling Line Identification (CLI), Call For-
warding (CF), Closed User Group (CUG), etc. Your
telephone company can provide more informa-
tion on Supplementary Services.
T carrier
system
The T carrier system, introduced by the Bell Sys-
tem in the U.S. in the 1960s, was the first suc-
cessful system that supported digitized voice
transmission. The original transmission rate
(1,544 Mbit/s) of the T1 line is in widespread use
today in enterprise connections to the Internet. A
higher multiplex level, the T-3 line, providing
44,736 Mbit/s, is also commonly used by Internet
service providers. Another commonly installed
service is fractional T1, which is the rental of some
portion of the 24 channels in a T1 line, with the
other channels going unused. The T carrier system
is entirely digital. The T1 (or T-1) carrier is the most
commonly used digital line in the United States,
Canada, and Japan. The T1 digital stream consists
of twenty-four 64-kbit/s channels. The T1 system
also uses 8,000 framing bits.
U interface
The reference point for connecting ISDN subscrib-
er equipment to the ISDN network in the USA,
Canada, Australia, and New Zealand. In these
countries, users may have to buy an NT-1 and sup-
ply it with power. The NT-1 is necessary in order to
connect European ISDN terminal equipment, such
as the IBM International ISDN PC Card, in these
countries. Note: Although the U interface also ex-
ists in Europe, it is not available to the subscriber.
The U interface has not been standardized in Eu-
rope and varies from one telephone company to
another. Thus North American ISDN devices can-
not be connected to the S/T interface of European
ISDN lines. Furthermore, European ISDN terminal
equipment cannot be directly connected to the U
interface, only to an NT-1.
Glossary
