BRI
BRI ISDN uses three separate channelstwo bearer (B) channels of 64Kbps each and a delta (D) channel of 16Kbps. B channels can be divided into 4 D channels, which allows businesses to have 8 simultaneous Internet connections. The B channels carry the voice or data, and the D channels are used for signaling.
The two B channels can be used independently as 64Kbps carriers, or they can be combined to provide 128Kbps transfer speeds.