A T card is used in the telephone office to provide service when it is relatively close to the telephone office. This is a 4 wire service (2 pairs).
An AIU (Access Interface Unit) is needed to extend ISDN service out a distance from the office. It provides a line code with higher voltages and a stronger signal. An NT1 device is needed on the terminal side to convert this line code back to a useful level. A 2B1Q off an AIU is the standard.