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”).
Appendix C. A brief ISDN glossary 229
