Nortel Modular ICS 7.1, Инструкция по установке, Страница: 54 / 700

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/ Welcome to ISDN
Modular ICS 7.1 Installer Guide N0130943 02
Comparing ISDN to Analog
ISDN offers significantly higher bandwidth and speed than
analog transmission because of its end-to-end digital
connectivity on all transmission circuits. Being digital allows
ISDN lines to provide better quality signaling than analog
POTS (plain ordinary telephone) lines. Also ISDN out-of-
band data channel signaling offers faster call setup and tear
down.
While an analog line carries only a single transmission at a
time, an ISDN line can carry one or more voice, data, fax and
video transmissions simultaneously.
An analog modem operating at 14.4 K takes about 4.5 minutes
to transfer a 1 MB data file, while a 28.8K modem takes about
half that time. Using one channel of an ISDN line, the transfer
time is reduced to only one minute. If two ISDN channels are
used, transfer time is just 30 seconds.
When transmitting data, the connect time for an average ISDN
call is about three seconds per call, compared to about 21
seconds for the average analog modem call.
Type of ISDN service
Two types of ISDN services (lines) are available: Basic Rate
Interface (BRI) and Primary Rate Interface (PRI). Each line is
made up of separate channels known as B and D channels
which transmit information simultaneously.
• BRI is known as 2B+D because it consists of
2 B-channels and one D-channel.
• PRI is known as 23B+D because it consists of
23 B-channels and one D-channel.