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While you've heard of ISDN, there's a good chance you're unsure whether you need it - or even what, exactly, it is. Even though ISDN is globally available, it's so new that understanding it may require a little investigation.

In simple terms, ISDN is a replacement for plain old telephone service, which was never designed to meet the needs of the information age. ISDN uses the same wiring that currently serves homes and businesses. You get ISDN service from the same companies who provide telephone service, and you use it to connect telephones, computers, and fax machines. The difference is that you get much faster, much more dependable connections for voice, data, fax, and even video - all through a single line. There is no other technology that comes close to delivering such communications benefits today.

International ISDN standards were established about 10 years ago. Since then, telephone companies throughout the world have raced to upgrade their equipment to ISDN standards. As ISDN service availability has spread, many millions of computer users have turned to ISDN, and new users are coming on board even faster.

What is the meaning of "ISDN"

ISDN stands for Integrated Services Digital Network.

"Integrated Services" refers to ISDN's ability to deliver two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of most people's complete communications needs, without forcing the purchase of multiple analog phone lines at a much higher transmission rate.

The "Digital" in ISDN refers to its purely digital transmission, as opposed to the analog transmission of plain old telephone service. If you're using a modem for Internet access at this moment, your Internet service provider's modem has converted this site's digital content to analog signals before sending it to you, and your modem converts those signals back to digital when receiving (the same thing happens with every keystroke and mouse click you transmit). When you connect with ISDN, there is no analog conversion. ISDN transmits data digitally, resulting in a very clear transmission quality. There is none of the static and noise of analog transmissions that can slow transmission speed.

"Network" refers to the fact that ISDN is not simply a point-to-point solution like a leased line. ISDN networks extend from the local telephone exchange to the remote user and include all of the telecommunications and switching equipment in between.

Benefits of ISDN

While ISDN accommodates telephones and fax machines, its most popular advantage is in computer applications. You can plug an ISDN adapter into a phone jack, like you would an analog modem, and get a much faster connection with no "line noise."

The most common ISDN service, Basic Rate Interface (BRI), provides two 64 Kbps channels per line. When the two channels are bonded in a single connection, you get a speed of 128 Kbps, which is about four times the actual top speed of the fastest analog modems. Compression can increase throughput to around 250 Kbps.

Telecommuters, for example, benefit immensely from ISDN. Whether you access the corporate LAN in the evenings or maintain a full-time, remote home office, ISDN is the next best thing to being there. E-mail, database access, and file transfers improve dramatically, making it seem like you're locally attached to the LAN.

Internet access is another great application for ISDN. Compared with even the fastest modem access, ISDN makes Web graphics appear almost immediately, and can reduce download times by over 75%. ISDN can even provide advantages over shared, higher-bandwidth office connections; PC Magazine advises that an ISDN connection can deliver better performance than a T1 shared among users on a LAN. And in many markets, it's actually cheaper than an isolated analog business line.

Such large-scale file transfer applications as medical imaging, insurance and law enforcement imaging, and the preparation of printed materials are additional arenas where ISDN proves highly beneficial. With the dramatic reduction in file transfer time, ISDN makes even multi-megabyte files available to recipients within minutes, not hours.

Videoconferencing is an emerging ISDN application that's growing fast in popularity, and ISDN is currently the only practical way of making it happen.

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