What is ISDN?

Integrated Services Digital Network (ISDN) is fully digital telephone service, providing data, voice, and video channels over the existing phone network. While most of the current phone network is already digital, ISDN replaces the final analog section connecting the local exchange with individual houses or offices to create a fully digital connection.

Not only is ISDN much faster than a standard analog telephone connection, but also its multiple channels allow you to use several devices (such as a telephone, computer, and fax) simultaneously on the same line.

You usually obtain ISDN service from a telephone company and Internet service provider. There are two different classes of ISDN: Basic Rate Interface (BRI) and Primary Rate Interface (PRI).

Basic ISDN (BRI) is designed to meet the needs of most individual users and small networks. It is fairly inexpensive and can use existing phone wiring. It divides the telephone line into three channels: two 64Kbps bearer channels (B channels) and one 16Kbps D channel for setting up and managing calls. In some situations, the two bearer channels can function together as a single virtual channel, with a data transmission speed of 128Kbps.

PRI ISDN is designed for organizations with greater capacity requirements. It uses a full T1 line, transmitting at 1.544Mbps. It offers 23 B channels at 64Kbps, and one 64Kbps D (setup) channel.

Using ISDN service requires an NT-1 terminator to connect with the phone company's lines, and a terminal adapter (sometimes imprecisely called an "ISDN modem") to connect to the computer. Some adapters have integrated NT-1s. Connecting several networked computers to the ISDN line involves using an ISDN router to connect to your hub. Some ISDN routers incorporate NT-1s and/or hubs.

You can find out more about ISDN at: http://www.informatik.uni-bremen.de/~henker/dank/

Note: ISDN is declining in popularity and cost-effectiveness as broadband services such as cable modems and DSL become more available.

Also see:

• At IU, how do I connect to the Internet?