ISDN

A telephone technology for simultaneous multiple uses

2 channels

Basic ISDN provides two high-speed connections on one ordinary telephone line.

2 uses

Each channel can carry voice or data.

An agent uses the two channels to simultaneously converse with a caller and access a database.

A supervisor or corporate database combines the two channels for data access four times as fast as a modem

23 channels

Primary Rate Interface (PRI) option supports 23 simultaneous voice or data connections on a single telephone line.

Integration

Distributed Call Center (DCC) uses ISDN to integrate computers and telephones. The public telephone network links callers, agents and supervisors, and databases.

Adaptability

ISDN is widely available, well defined, and compatible with all central office switches.

ISDN uses existing standards and technologies, and is growing in momentum.

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http://www.compuvar.com/doc-02-02.html-ssi

ISDN - How It Works

ISDN is an entirely digital connection, and so you really do get 64k per channel on each connection - in both directions.

Your ISDN adapter is in constant contact with the telephone company switch whenever it is switched on and initiated. This means that when you "dial" a number that information is processed by the switch immediately (no wait for a dial tone). Then the connection through to the destination number is established digitally also (no ringing tone or modem tones), so the whole process takes around 1 second, as opposed to 20-40 seconds with a modem.

You can use one or both of the ISDN B-channels for voice when you are not using it for data, giving you a much clearer connection because, at least between you and your destination's telephone company switch, the connection is digital.