Section 6.1: ISDN An Overview of Its Capability

The telephone companies have been revising their networks for a long time. The first objective was to automate long distance dialing, eliminating the need for an operator to place the call. This was accomplished in the 1950s through Direct Distance Dialing (DDD). The next objective was to provide a network which would provide end-to-end connectivity, access and service integration and standard interfaces and would allow customers to have more control over the services they needed. The Integrated Services Digital Network (ISDN) addresses these objectives.

ISDN provides a standard interface for all types of digital transmission. Digitized voice, low- and high-speed data, video, facsimile, and imaging can be sent over ISDN facilities, using a common pair of copper wire, coaxial cable, or fiber optics. ISDN provides end-to-end connectivity and digital transmission over the local loop.

ISDN is as much a concept as a technical solution. Talks about an integrated network began in the 1960s, as telephone companies began to research ways to consolidate their facilities. It had already become apparent that circuits riding on copper cable were in high demand, and the telephone companies needed a plan to consolidate their facilities before they ran out of copper.

ISDN as a concept implies that the whole public network is integrated. Integrated means that all transmissions, voice, data, and video, can use the same facility instead of using separate specialized circuits. Digital network means that all transmissions must be converted into a digital format so they...