ISDN is a digital, worldwide public standard for sending voice, video, data or packets over the public switched telephone network (PSTN). It enables customers to transmit voice, data and video with one or two pairs of wires. As previously mentioned, there are two “flavors” of ISDN: basic rate (BRI), and primary rate (PRI), which are defined in Table 6.3.
Both types of ISDN have these important characteristics:
Digital connectivity to achieve consistent, high-quality voice.
Out-of-channel signaling— Calls are set up quickly; each voice/data channel uses all of the bandwidth for user data. The signaling channel is available for packet service such as alarm monitoring.
A switched service— Users pay long distance ...