DIVA T/A ISDN Modem Reference Guide ◆ Page 4
What is ISDN?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.
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.
ISDN stands for Integrated Services Digital Networ k
“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 d ata
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” refe rs to the fa ct that IS DN is not si mply a point -to-point s olution lik e a leased line.
ISDN networks extend from the local telephone exchan ge to the remote user and include all
of the telecommunications and switching equipment in between . When you have ISDN, you
can make connections throughout the world to other ISDN equipment. If your ISDN
equipment includes analog capabilities, you can also connect to analog modems, fax
machines, and telephones, even though they may be connected to plain old telephone
service.
Benefits
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 fastes t analog modems. Compression can increase
throughput to around 250 Kbps.