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| Networks (ISDN) WHAT IS IT..? | ||||||||||||||||||||||||
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Integrated Services Digital Network (ISDN) ISDN stands for Integrated Services Digital Network - the name for digital telephone service that works over existing copper telephone wiring. There are several types of ISDN service, but the most appropriate type for individual computer users, and the type that this site focuses on, is the ISDN Basic Rate Interface (BRI). Basic Rate ISDN divides the telephone line into 3 digital channels: 2 "B" channels and one "D" channel, each of which can be used simultaneously. The B channels are used to transmit data, at rates of 64k or 56k (depending on your telephone company). The D channel does the administrative work, such as setting up and tearing down the call and communicating with the telephone network. With two B channels, you can make two calls simultaneously. Most of the world's existing telephone network is already digital. The only part that typically isn't digital is the section that runs from the local exchange to your house or office. ISDN makes that final leg of the network digital. Availability Unlike analog telephone service, ISDN service is not yet available everywhere. Your telephone company must have installed the necessary equipment in the central office that serves you. Because ISDN is a digital service, it is very sensitive to outside interference. You must be within a given distance of the telephone company equipment that serves you (typically 18,000 feet). Further, there can not be any other anomalies near the wiring that might interfere with the transmission. As a result, even if the equipment is installed at the central office, it is possible you will not be able to get ISDN due to line interference or your distance from the central office. To determine whether your particular wiring will support ISDN, the telephone company will perform what is known as a line qualification. Some telephone companies offer what is called "ISDN Anywhere", which means if you order ISDN, they will find a way to get it to you. In cases where the telephone company does not have the right equipment in the local central office that serves you, they can use "line extension" technology to serve you from another exchange. The use of line extension technology may significantly increase the cost of your ISDN service. Generally, ISDN has better availability in urban and suburban areas, and is harder to get in rural areas | |||||||||||||||||||||||
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