The U.S. standard for ISDN-PRI consists of 24 digital channels: 23 B channels and 1 D channel, commonly referred to as a 23B+D connection. ISDN-PRI provides a total bandwidth of 1.544 megabits per second and is designed for transmission over a North American - standard T1 line connection. The European standard for ISDN-PRI provides a total of 31 or 32 digital channels. Each of these channels is a 64 – kilobit per second B channel, except one that is the D channel for the entire group. In Europe, ISDN-PRI is designed for transmission over a European-standard E1 line connection. A PRI D channel can be used to control one or multiple T1 or E1 lines.
The following figure illustrates the main difference between BRI and PRI, which is the greater number of channels that allows PRI to provide higher bandwidth than the BRI service.
MHMiriam HarlineFigure 4.1 Comparison of ISDN-BRI to ISDN-PRI