What is ISDN? ISDN, which stands for integrated services digital network, is a system of digitizing phone networks which has been in the works for over a decade. This system allows audio, video, and text data to be transmitted simultaneously across the world using end-to-end digital connectivity. The original telephone system used analog signals to transmit a signal across telephone wires. The voice was carried by modulating an electric current with a waveform from a microphone. The receiving end would then vibrate a speaker coil for the sound to travel back to the ear through the air. Most telephones today still use this method. Computers, however, are digital machines. All information stored on the