What is ISDN?
ISDN [I*SD'N] n. 1. Integrated Services Digital Network. 2. A digital telephone service that provides fast, accurate data transmission over existing copper telephone wiring. 3. The way fast way to go online.
The Basics
ISDN is based on a number of fundamental building blocks. First, there are two types of ISDN "channels" or communication paths:
- B-channel
The Bearer ("B") channel is a 64 kbps channel which can be used for voice, video, data, or multimedia calls. B-channels can be aggregated together for even higher bandwidth applications.- D-channel
The Delta ("D") channel can be either a 16 kbps or 64 kbps channel used primarily for communications (or "signaling") between switching equipment in the ISDN network and the ISDN equipment at your site.
These ISDN channels are delivered to the user in one of two pre-defined configurations:
- Basic Rate Interface (BRI)
BRI is the ISDN service most people use to connect to the Internet. An ISDN BRI connection supports two 64 kbps B-channels and one 16 kbps D-channel over a standard phone line. BRI is often called "2B+D" referring to its two B-channels and one D-channel. The D-channel on a BRI line can even support low-speed (9.6 kbps) X.25 data, however, this is not a very popular application in the United States.
- Primary Rate Interface (PRI)
ISDN PRI service is used primarily by large organizations with intensive communications needs. An ISDN PRI connection supports 23 64 kbps B-channels and one 64 kbps D-channel (or 23B+D) over a high speed DS1 (or T-1) circuit. The European PRI configuration is slightly different, supporting 30B+D.BRI is the most common ISDN service for Internet access. A single BRI line can support up to three calls at the same time because it is comprised of three channels (2B+D). Two voice, fax or data "conversations," and one packet switched data "conversation" can take place at the same time. Multiple channels or even multiple BRI lines can be combined into a single faster connection depending on the ISDN equipment you have. Channels can be combined as needed for a specific application (a large multimedia file transfer, for example), then broken down and reassembled into individual channels for different applications (normal voice or data transmissions).
ISDN offers the speed and quality that previously was only available to people who bought expensive, point-to-point digital leased lines. Combined with its flexibility as a dial-up service, ISDN has become the service of choice for many communications applications. Popular ISDN applications include:
- Internet access
- Telecommuting/remote access to corporate computing
- Video conferencing
- Small and home office data networking
Why Should I Use ISDN to Access the Internet?
More and more people are discovering that ISDN is the right Internet answer.
As the Internet becomes more and more information-intensive with graphics, sound, video and multimedia, your ability to take advantage of these new resources depends on the speed of your Internet connection. Can your existing connection handle these large files quickly and cleanly? Does it take forever to download files? Are your downloads frequently aborted because of transmission errors?
With ISDN, your Internet access is:
- Even faster
By combining your two B-channels you have access to up to 128 kbps -- more than four times as fast as a 28.8 kbps modem on a standard phone line. And ISDN's digital technology assures you the cleanest connection to the Internet so you won't be slowed down by re-transmissions because of old analog technology.
- More efficient and economical
ISDN brings increased capabilities, reduced costs and improved productivity to organizations both large and small. When you're looking for something on the Internet, you can get there faster. You can be more productive because you aren't waiting as long to get to that next website or download that large file.
For More Detailed Information on ISDN
Please check out the following ISDN resources:
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