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).
What Do I Use It For?
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:
