ISDN stands for Integrated Services Digital Network - the name for digital telephone service that works over existing copper telephone wiring. ISDN is a high-speed, fully digital telephone service. This means graphics, audio, and video transfer much faster, and download time is substantially decreased. ISDN transmits data digitally and, as a result, is less susceptible to static and noise than analog transmissions.
Data connections are virtually error-free.
Analog modem connections must dedicate some bandwidth to error correction and retransmission. This overhead reduces the actual throughput, while an ISDN line can dedicate all its bandwidth to data transmission. In addition to raw speed, ISDN calls can be set up much faster than analog phone calls. Because ISDN is fully digital, the lengthy handshaking process of analog modems is not required.