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ISDN stands for integrated services digital network. Voice and data
are carried by bearer channels (B channels) occupying a bandwidth of
56 - 64 KBps (the latter being the standard). A data channel (D
channel) handles signaling at 16 or 64 KBps, depending on the service
type. |
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Two types of ISDN service are basic rate interface (BRI) and primary
rate interface (PRI). BRI consists of two 64 KBps B channels and one
16 KBps data channel for a total bandwidth of 144 KBps. PRI is
intended for users desiring greater bandwidth. It consists of 23 64
KBps B channels plus on 64 KBps D channel for a total bandwidth of
1536 KBps. In Europe, PRI consists of 30 64 KBps B channels and on 64
KBps D channel for a total bandwidth of 1984 KBps. It is also
possible to support multiple PRI lines with one 64 KBps D channel
using non-facility associated signaling (NFAS). |
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ISDN's greatest challenge to being accepted as a viable connection to
the Internet is it's price. The first item is the ISDN modem. Some
ISDN modems run as high as $400, but most are around $200 - $250.
ISDN providers usually have to install some additional wiring, but at
least they can utilize the standard phone lines that are already
there. Service rate charges come from both the telephone company and
the Internet service provider (ISP). The service rates can vary for
the phone company where they charge a monthly fee plus 1-2 cents per
minute. That does not sound like a lot, but, if you wanted 24/7
service, that runs roughly $650 / month. |
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