Techopedia explains Basic Rate Interface (BRI)

ISDN has enabled the reliable transmission of data where multiple users can make use of the service lines at the same time. This network architecture is economical for small industries and homes where dedicated lines, modems and cabling expenses must be kept low. A bearer channel has a bit rate of 64 Kbps, whereas a data channel is 16 Kbps. Two bearer channels can be combined by channel bonding to give an aggregated data rate of 128 Kbps. B channels have dedicated bandwidth and transmit data via a formatted and circuit-switched channel, whereas D channels transmit data in the form of packets. The format of data communication in the D channel has become the basic type of frame relay.