ISDN stands for Integrated Service Digital Network, but it is most commonly called ISDN. This is one of the oldest high-speed digital access methods. It was used and at some places is still used by individual consumers and businesses to connect to the Internet. ISDN is a telephone data service standard which is used in the 90s before DSL was made available or came in to existence. ISDN was used even before the cable modem technologies became popular. Broadband service is always compared to ISDN for speed as ISDN was the standard high-speed access technology to form the baseline for the challenges to the broadband. Even today ISDN is used for comparisons after the introduction of new technologies.