.) The local telephone companies use in band signaling right 230 The Telecom Handbook CHAPTER 10 Figure 10.10 BRI ISDN Telephone B CHANNEL PUBLIC B CHANNEL Telephone B CHANNEL SWITCHED B CHANNEL Computer NETWORK D CHANNEL D CHANNEL Computer on the same line as the transmission with POTS lines. Signals such as tones take up transmission time that could be more effi- ciently used for transmitting voice and data. There are two ISDN interfaces: Basic Rate Interface and Pri- mary Rate Interface. Basic Rate Interface (BRI) (Figure 10.10) is usually described as 2B+D. That means it has two bearer chan- nels and one data channel or D channel. The B channels carry the content of the call that may be voice, high speed data or video. Each B channel carries 64 kilobits per second. The D channel carries the call delivery information, such as the telephone num- ber of the calling party. The D channel carries 16 Kbps. The PRI (Primary Rate Interface) is described as 23B+D for a total of 24 channels, the same as a T-1. PRI is what happens when ISDN meets T-1. In addition to the ISDN service and compatible telephone and computer equipment you also need a Terminal Adapter and a Network Termination Device known as NT-1. Sometimes the NT- 1 is built into the terminal adapter. Applications for ISDN include the following: Ability to send and receive data rapidly makes it popular for credit card processing. Internet users do not have to wait a long time for graphics to appear on the computer screen. (ISDN for this application is being replaced by dedicated high speed lines such as DSL or Cable Modems) The Telecom Handbook 231 OUTSIDE LINES ANI (Automatic Number Identification) delivered on ISDN enables you to capture the telephone number of the person calling you, enabling you to accept, reject, ignore or redirect incoming calls. Desktop video conferencing is accomplished by bonding to- gether the 2 B channels to provide sufficient bandwidth for video transmission. DDS Circuits DDS Service (Dataphone Fixed Digital Service) is a basic d