ISDN – Integrated Services Digital Network
ISDN is a type of digital phone/data and internet service that preceded ADSL (asynchronous digital subscriber line) and has for the most part been superceded by it.
Normal telephone lines carry analog signals that must be amplified and converted to digital signals by the phone company. This process introduces not a slight lag time, but also distortion in the signal. Dial-Modems and telephone are examples of equipments that use analog signals.ISDN makes use of digital signals running along existing copper lines to increase the data throughout, reduce line noise and enhance signal quality. In the mid 1990s, ADSL was very expensive not widely available. Companies and individuals wanted a faster way to connect to the internet; but the technology behind dial-up modems had reached its threshold. ISDN became a viable alternative to provide speeds of up to 128 kilobits per second, versus the standard connection of 30-53 kbps with a dial-up modem.
The most common type of ISDN service for internet onnection is the Basic Rate Interface, ISDN BRI. This technology creates two B-channels on the existing copper lines of 64 kbps each, along with a single 16 kbps D-channel for the hone line. This separates data channel from the voice channel, allowing telephone or fax use while online.
While ISDN is inexpensive and about twice as fast as dial-up service. It has been largely replaced by affordable DSL service. An inexpensive ADSL service offers speeds up to 384 kbps, while more expensive versions are improving in speed all the ime. As of fall 2005, standard ADSL speeds range between 1.5 and 3.0 mbps, or 1536-3072 kbps. Although isdn may not be the best choice for packet-switching networks like the internet, it is till likely used for professional audio and broadcast applications where digital clarity with integrated services is specifically required. Small businesses that often used two voice lines, such as phone and fax, and only require limited internet connectivity, say, an hour or less per day , may prefer an isdn. Isdn might also be a better choice of high-speed connections to ntranets for video conferencing, or to remote networks other than the internet.
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Communication Engineering, Seminar reports | Admin September 25, 2009