In the Integrated Services Digital Network (ISDN), the B-channel is the channel that carries the main data. (The “B” stands for “bearer” channel.)n ISDN, there are two levels of service: the Basic Rate Interface, intended for the home and small enterprise, and the Primary Rate Interface, for larger users. Both rates include a number of B- (bearer) channels and a D-channel. The B-channels carry data, voice, and other services. The D-channel carries control and signaling information.
The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate Interface user can have up to 128 Kbps service. The Primary Rate Interface consists of 23 B-channels and one 64 Kpbs D-channel in the United States or 30 B-channels and 1 D-channel in Europe.
I copy pasted below:
B channel (bearer) is a telecommunication term which refers to the ISDN CHANNEL in which the primary data or voice communicatoin is carried. It has a bit rate of 64 kbit/s in full duplex