请问关于30B+D...

各位高手，能具体说一下30B+D的具体吗？

B channels B channels are the bearer channel. They are used to carry voice or data information and have speeds of 64 kbps.Since each ISDN line (BRI or PRI) has more than one B-channel, more han one transmission can occur at the same time, using a single ISDN line. D channels The standard signaling protocol is transmitted over a dedicated data channel called the D-channel. The D-channel carries call setup and feature activation information to the destination. This channel has speeds of 16 kbps (BRI) and 64 kbps (PRI). Data information consists of control and signal information and packet-switched data such as credit card verification.