Short form for "Basic Rate ISDN," which is a digital telephone service available to end users. Basic rate ISDN provides two digital "B" channels over a single twisted-pair line, along with two telephone numbers, and a signalling channel. Each "B" channel provides 64 kbps data rates with latencies close to DSL - 30 to 50 ms - and an ISDN router or terminal adapter could use Multilink PPP to combine both channels to get 128 kbps.

You may use an ISDN telephone to place voice calls, or a terminal adapter with analogue jacks to use regular phones to place calls. The more advanced terminal adapters, such as Motorola's BitSURFR series, can even automatically terminate digital calls to make room for an analogue call. This is especially useful when you use both digital channels to get 128 kbps service, and you don't want to miss calls in the meantime.

B-ISDN was more useful during the late 1990s when DSL and cable were only being tested. In Canada, B-ISDN service was available for roughly the same cost as two analogue telephone lines, though it was up to the customer to find an Internet provider or data provider on their own. Providers that supported v.90, K56Flex or X2 56k analogue modem technology supported ISDN callers transparently, whether they realized it or not.

Since 2000, B-ISDN lost popularity with the rise of cable and DSL Internet services, though you will still find ISDN customers using their connections with direct payment, direct debit or credit card readers. It is still possible in 2005 to use B-ISDN with 56k dial-up Internet providers, and it can be a suitable replacement for customers unable to use DSL or cable because of distance or location problems.

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