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What is ISDN?

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Integrated Service Digital Network, or ISDN, is the original high-speed internet service. It sparked the high-speed internet development between service providers during the 1990's and, of course, revolutionized internet use. Much like its predecessor, the dial-up internet service, ISDN utilizes a phone line. In fact, it set the standard for telephone data service.

ISDN internet service was the improvement upon dial-up, and it also paved the way for DSL and cable-modem internet service thereafter. It can be considered the step of internet evolution that lies between dial-up and DSL/Cable. Modernizing internet use and bringing high-speed access inside the home, ISDN became the standard by which rival broadband internet service providers competed. Although ISDN internet service still exists, like the dial-up connection it is being replaced by faster and cheaper services that the broadband companies are providing. Regardless, broadband high-speed internet service is still compared with ISDN today since they both represent the standard of their times.

ISDN internet service is basically a telephone-based network system that operates by a circuit switch, or dedicated line. It can transmit data and phone conversations digitally over normal telephone wires. This makes it both faster and of higher quality than dial-up internet service. During the 1990's this revolutionized the way people did business. No longer would you have to miss a call in order to access your internet, or shut down the internet to make a telephone call. As such, ISDN internet service made video teleconferencing not only possible, but very popular at this time as well.

There are two different types, or lines, of ISDN internet service. The first is a basic rate ISDN line. Called a Basic Rate Interface (BRI), this line has two data, or bearer, channels that operate at 64 kbit/sec. Two or more ISDN-BRI lines can be combined as well, yielding speeds of 256 kbit/sec. Combining these lines is common for video conferencing use or for transmitting data at higher speeds. The second type of ISDN line is called a primary rate line, or Primary Rate Interface (PRI). This line had 23 bearer channels and has a total speed of 1,544 kbit/sec. It is used mostly for telephone communication rather than data transmission, particularly within companies that have large, private telephone exchange systems operating inside their business.

The advantages of having ISDN internet service definitely lies in the data lines themselves. Not only do you have constant data speed via these lines, each bearer channel runs at 64 kbit/sec with the ability to be combined to reach greater speeds. ISDN internet serviced also allows for multiple data transmission, so telephone calls and data downloading are no longer mutually exclusive. The disadvantages, however, is that the digital clarity of ISDN voice communication and its speedy data transmission come at an extra cost. ISDN is billed like a phone line, but with an added cost for service. And although its operational distance from the ISDN central office is greater than that for DSL, its terminal adaptor (similar to a modem) is more expensive than DSL or cable modems. While this equipment and service continue to remain costly, it is leaving the way open for other internet services, like broadband, to quickly replace ISDN's share of the marketplace.

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