A B Channel is the bearer channels on an Integrated Services Digital Network (ISDN) Primary Rate Interface (PRI) T1 phone service. In a typical ISDN PRI configuration, there are 23 B channels (voice) and one PRI D channel (signaling, control, call data), this is known as a 23B+D configuration. ISDN PRI service is used by businesses to provide local and long distance voice service as well as other applications including video conferencing, fax, and dial-up. The PRI B channels provide the call capacity while the D channel provides increased efficiency through a PBX phone system by setting up and breaking down the PRI phone calls faster than a regular voice T1 or phone lines, providing robust features like Caller ID, Direct Inward Dialing (DID), and advanced call routing. PRI B Channels are also known as the Bearer Channels or Voice Channels.