The definition of ISDN

An integrated service digital network line can be simply looked at as a digital phone line. ISDN connections to the Internet can be four times faster than the fastest regular phone connection, and because it is a digital connection a modem is not needed. Any computer hooked up to ISDN will typically require other special equipment in lieu of the modem, however. Also, both phone companies and ISPs charge more for ISDN connections than regular modem connections.