Basic Rate ISDN uses digital transmission that divides its bandwidth into three channels. Two of these transmit data at 64 Kbps, and the third at 16 Kbps. The 64 Kbps channels can carry voice, data or images. The slower 16 Kbps channel carries signaling data.
A computer connected to an ISDN service can use both the 64 Kbps channels to have a 128 Kbps data stream.