Integrated Services Digital Network (ISDN) lines are also available from many local
telephone companies. ISDN is an upgraded phone line that can be used for faster
Internet access and for regular voice calls. Using one line, you can talk on the phone
while you’re surfing the Web. Like DSL, ISDN is all digital, which means that data
doesn’t have to be converted to an analog signal for transmission.
The ISDN service intended for residential use is Basic Rate Interface (BRI). On one
ISDN line, BRI provides two 64-Kbps channels, or B channels, and one 16-Kbps channel,
or D channel. The D channel is mostly used for signaling—for instance, to indicate that
the line is busy. The B channels are where the action is. When the two B channels are
combined, you have a 128-Kbps line to the Internet. That’s roughly twice the speed of
the fastest analog modem, 56 Kbps. If you want to talk on the phone or send a fax, your
Internet access drops down to one 64-Kbps B channel, while the other B channel is used
for voice. Integrated Services Digital Network (ISDN) lines, like DSL lines, are all-digital,
high-speed phone lines that provide a faster way to connect to the Internet.
To connect your computer to an ISDN line, you need an ISDN adapter, which is like
a modem. The cost of an ISDN line usually depends on the number of minutes of use.
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