With ISDN standard, one of circuit grades logical forms the connected specification of
communications network. Those where it is used as the channel for communication are the B channel.Vis-a-vis this, the signal and the logical circuit does the communications control of the B channel in order which to offer addition functionare calledthe D channel.WithISDN standard, 1 physical circuit, is formed with combinationof the plural Bchannels and the D channel. As for transfer rate of B per 1 channels 64kbps.With ISDN service(INS net64)for the general home the B channel stopping, 2andthe D channel 1, with service (INS net1500) for the enterprise 23 B channelsand Dchannel 1 oven 1 physical circuit is formed.