What is ISDN?

ISDN (which stands for Integrated Services Digital Network) is a system of digitising phone networks which allows audio, video, and text data to be transmitted simultaneously across the world using end-to-end digital connectivity. It is a faster, more reliable way of transmitting data than regular analogue modems.

ISDN allows multiple digital channels to be operated simultaneously through the same regular phone jack in a home or office. The change comes about when the telephone company's switches are upgraded to handle digital calls. Therefore, the same wiring can be used, but a different signal is transmitted across the line.

Previously, it was necessary to have a phone line for each device you wished to use simultaneously. For example, one line each for the phone, fax, computer, and live video conference. Transferring a file to someone while talking on the phone, and seeing their live picture on a video screen would require several expensive phone lines.

ISDN adds capabilities not found in standard phone service. The main feature is that instead of the phone company sending a ring voltage signal to ring the bell in your phone, it sends a digital package that tells who is calling (if available), what type of call it is (data/voice), and what number was dialled (if multiple numbers are used for a single line). ISDN phone equipment is then capable of making intelligent decisions on how to answer the call. In the case of a data call, baud rate and protocol information is also sent, making the connection instantaneous.