Integrated Services Digital Network, a type of digital telephone service capable of operating at 128 Kbps, or up to 18 times the speed of standard dial-up modems. This service is available as an alternative delivery method for Internet access using standard telephone lines. ISDN service must be carried on fiber-optic cable, and the demand for high-speed Internet access is so high that most of the industrialized world is scheduled to have its existing telephone infrastructure upgraded to fiber-optic cable by the end of decade one.