Integrated Services Digital
Integrated Services Digital Network (ISDN) is
comprised of digital transmission and data-transport services
offered by telephone carriers. ISDN involves the digitization
of the telephone network, which permits voice, data, text, graphics,
music, video, and other source material to be transmitted over
existing telephone wires. Home and business users who install
an ISDN adapter replacing a telephone modem receive surfing speed
up to 128 Kbps compared with the maximum 56 Kbps rate of a modem
ISDN requires adapters at both ends of the transmission so your
access provider also needs an ISDN adapter. ISDN is generally
available from your phone company in most urban areas. ISDN applications
include high-speed image applications, additional telephone lines
in homes to serve the telecommuting industry, high-speed file
transfer, video conferencing and voice service. In many areas
where DSL and broad band services are now offered, ISDN is no
longer as popular an option as it was formerly.
There two types of services associated with ISDN service. These
two levels of service are known as the Basic Rate Interface (BRI),
intended for the home and small enterprise, and the Primary Rate
Interface (PRI), for larger users. BRI and PRI both interfaces
include a number of B-channels and D-channels. Each D-channel
carries control and signaling information and each B-channel carries
data, voice, and other services.
ISDN BRI Service
The ISDN Basic Rate Interface (BRI) service offers two B channels
and one D channel (2B+D). BRI B-channel service operates at 64
kbps and is meant to carry user data; BRI D-channel service operates
at 16 kbps and is meant to carry control and signaling information,
although it can support user data transmission under certain circumstances.
Thus, a Basic Rate user can have more than 128 Kbps service.
ISDN PRI service
ISDN Primary Rate Interface (PRI) service offers 23 B channels
and 1 D channel in North America and Japan, yielding a total bit
rate of 1.544 Mbps. ISDN PRI in Europe, Australia, and other parts
of the world provides 30 B channels plus one 64-kbps D channel
and a total interface rate of 2.048 Mbps.
ISDN in concept is the integration of both analog or voice data
together with digital data over the same network. The broadband
ISDN (B-ISDN) is capable of providing all these integrated services
(voice, data, video, etc.) through a single interface just like
ISDN was supposed to but it will do it a lot faster than ISDN
could. B-ISDN is intended to support transmission from 2 Mbps
up to much higher, moving faster than ISDN, but it is still quite
a ways off.
ISDN has been very slow in coming. In fact, many people consider
them to be out of date already. ISDN is available now in many
places, but it is not widely used. Further most of the products
and services that people have forecast for ISDN are still not
available. For this reason many people say that ISDN also stands
for "It Still Does Nothing".
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is ISDN (Integrated Services Digital Network)?
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