modems :: essays research papers

Does the humble telephone lines play a study role in shaping the third millennium? Can a mere pair of thin copper wires twisted around individually other transmit net profit data reliably and securely at blazing fast speed, making it possible to view high-quality moving images, go bad and vast amounts of data on your personal computer screen or television? The answer is yes, as the growing success of DSL (digital lecturer line) technology abundantly demonst place. The mental ability of a communications channel depends on its bandwidth and its signal-to- hoo-ha ratio. A voice connection through a pompous phone network employments a bandwidth of around 3,000 hertz (Hz) from about three hundred Hz to 3,300 Hz. An analog modem operating at 33.6 kilobits per second (kbps) requires a more or less wider bandwidth 3,200 Hz and needs a very good connection, one with a high signal-to-noise ratio. Modems operating at 56 kbps achieve their rates by taking advantage of digital connecti ons that circumvent some sources of noise in transmissions toward the end user. But these bit rates are furthermost from the maximum possible on a twisted pair alone. adept process that limits bandwidth and signal strength is the steady attenuation of the signal as it travels down the line, with the higher frequencies being affected more severely. Greater capacity is therefore available if the lines are kept short. Originally, the Discrete Multitone approach was intend for sending entertainment video everywhere telephone wires. Because such use relies principally on one-way transmission, most of the sub conduct were devoted to the downstream signal, carrying about 6 Mbps, with about 0.6 Mbps available in the other direction. This unsymmetrical contour line of DSL has become k instantlyn as ADSL, and the signal coding is now a worldwide standard. Although the video application has not yet borne fruit, asymmetric transmission fortuitously lends itself to browsing on the World Wid e Web. all over the past year ADSL has begun to be widely installed in telephone networks for always-on Internet access, typically operating at several hundreds of kbps or higher over phone wires up to about 5.5 kilometers in length. The beauty of ADSL, unlike the multilevel coding used in HDSL, is that the data can use channels operating above the voice frequency band, so a exclusive phone line can simultaneously transmit voice and high-velocity data. The newest standard of ADSL is G lite which is just for home users, a world-wide standard that limits the data rates to 1.