Chapter 9: Planning for and Installing ISDN

Today, almost all NYNEX central offices have at least one digital, ISDN-capable switch installed. Plans indicate that by the end of the decade, virtually all switches throughout the NYNEX area will be either AT&T 5ESS or Northern Telecom DMS-100 systems - both digital switches designed to support the ever-growing range of advanced telecommunications services, including ISDN.

NYNEX is also implementing a Virtual ISDN program that allows users in areas not yet served by an ISDN switch to obtain ISDN lines "imported" from a nearby central office. While these remote Virtual ISDN connections may require a change in telephone numbers when a customer's local switch does become ISDN-ready, they can and do offer access to ISDN today..

In addition, NYNEX is working to overcome the technical restriction that limits ISDN connectivity to a distance of about 18,000 feet (slightly less than three and a half miles) from the user's local telephone switch. Using line boosters, that distance can be effectively doubled.

The goal of both these programs is to enable any individual or company in the NYNEX "footprint" to obtain ISDN by the end of 1995. Both programs do incur small additional installation and monthly charges.

ISDN is also being broadly implemented in many other areas of the United States. Through the long-distance ISDN services of the major interexchange carriers (IECs) such as AT&T, MCI or Sprint, dialed digital connections can now reach out to locations throughout the nation and the world. For international applications, many European and Pacific Rim countries also offer ISDN connections to most overseas commercial centers.

Which means that it is now increasingly practical to begin implementing even the most ambitious worldwide telecommunications strategies using the high-speed digital connections of ISDN to "close the loop" to user desktops around the globe.

Extending an Application with Switched 56

For applications that extend into areas still not served by ISDN, it is also possible to use universally available Switched 56 services offered by all regional and interexchange carriers. These are single-channel, dialed, data-only connections, capable of uncompressed data speeds up to 56Kbps.

All Switched 56 services are connected to the nationwide networks of the interexchange carriers, and thus to each other. The result: ISDN applications can be successfully extended through Switched 56 if they do not require voice, do not use two channels simultaneously, and do not depend on D-channel signaling.