is a circuit-switched telephone network system that transmits both data and voice over a digital line. You can also think of it as a set of communication standards to transmit data, voice, and signaling. These digital lines could be copper lines. The basic advantage of ISDN is to facilitate the user with multiple digital channels. ISDN provides high data rate because of digital scheme which is 56kbps. ISDN network lines are able to switch manifold devices on the single line such as faxes, computers, cash registers credit cards readers, and many other devices.