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Appendix C. A brief ISDN glossary 229
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 subscriber equipment
to the ISDN network in the United States of America, Canada, Australia, and
New Zealand. In these countries, users might have to buy an NT-1 and supply
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 exists in Europe, it is not
available to the subscriber. The U interface has not been standardized in
Europe and varies from one telephone company to another. Thus North
American ISDN devices cannot 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.
• Warm insertion/removal - Denotes the installation or removal of a peripheral
device when the system is in suspend or hibernation mode (also called “sleep
mode”).
ISDNmst.fm Page 229 Wednesday, January 15, 2003 9:22 AM