The International Telecommunication Union(ITU-TS) standardized,interfacestandardof the ISD Ncircuit. As for transmission speed 144kbps.

In the same wayas other interface standard, it stipulates 1 physical circuit the plural hypothetical circuits (the channel) as gathering.

As for BRI, "the Bchannel "of 64kbps consists of 2 and "D channel" 1 of 16kbps. This system is called "2B+D" and so on.

The B channel mainly in sending and receiving of the data and sound,the D channel it is used in order to exchange the data for line control of arrival and departure trust and the like. Because2 theseB channels are independent, while someone using the telephone, another personconnectsto Internet, and so on method of using is possible.