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ISDN |
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SDN (Integrated Services Digital Network) is a set of CCITT/ITU standards
for digital transmission over ordinary telephone copper wire as well as over
other media. Home and business users who install an ISDN adapter (in place
of a telephone modem) receive Web pages at up to 128 Kbps compared with
the maximum 56 Kbps rate of a modem connection. 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 in the United States and Europe. In many areas where DSL and cable
modem service are now offered, ISDN is no longer as popular an option as
it was formerly.
There are two levels of service:
the Basic Rate Interface (BRI), intended for the home and small enterprise,
and the Primary Rate Interface (PRI), for larger users. Both rates include
a number of B-channels and a D-channels. Each B-channel carries data, voice,
and other services. Each D-channel carries control and signaling information.
The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps
D- channel. Thus, a Basic Rate user can have up to 128 Kbps service.
The Primary Rate consists of 23 B-channels and one 64 Kpbs D-channel
in the United States or 30 B-channels and 1 D-channel in Europe.
ISDN in concept is the integration of both analog or voice data together
with digital data over the same network. Although the ISDN you can install
is integrating these on a medium designed for analog transmission, broadband
ISDN (BISDN) is intended to extend the integration of both services
throughout the rest of the end-to-end path using fiber optic and radio
media. Broadband ISDN encompasses frame relay service for high-speed data
that can be sent in large bursts, the Fiber Distributed-Data Interface (FDDI),
and the Synchronous Opical Network (SONET). BISDN is intended to support
transmission from 2 Mbps up to much higher, but as yet unspecified, rates.
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