modems :: essays research papers

Does the humble tele resound lines play a major quality in shaping the third millennium? Can a specified pair of thin copper wires twisted around each opposite transmit Internet data reliably and securely at blinding fast speed, making it possible to view extravagantly-quality moving images, sound and gigantic amounts of data on your personal computer screen or television? The answer is yes, as the growing success of digital subscriber line (digital subscriber line) applied science abundantly demonstrates. The capacity of a communications channel depends on its bandwidth and its signal-to-noise ratio. A voice connection through a conventional think network uses a bandwidth of about 3,000 hertz (Hz) from about 300 Hz to 3,300 Hz. An analog modem operating(a) at 33.6 kilobits per second (kbps) requires a slightly 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 advantag e of digital connections that circumvent some sources of noise in transmittings toward the end user. But these bit rates are far from the maximum possible on a twisted pair alone. One bring that limits bandwidth and signal strength is the steady attenuation of the signal as it travels conquer the line, with the higher frequencies being affected more severely. Greater capacity is consequently available if the lines are kept short. Originally, the Discrete Multitone approach was intended for move entertainment video over tele call back wires. Because such use relies generally on one-way transmission, most of the subchannels were devoted to the downstream signal, carrying about 6 Mbps, with about 0.6 Mbps available in the other direction. This asymmetric form of DSL has become known as ADSL, and the signal cryptanalytics is now a worldwide measuring stick. Although the video application has not yet borne fruit, asymmetric transmission fortuitously lends itself to browsing on t he World Wide Web. Over the past(a) 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 single phone line can simultaneously transmit voice and high-speed data. The newest commonplace of ADSL is G lite which is just for home users, a global standard that limits the data rates to 1.