Adsl The Signal On Your Line example essay topic
Modems operating at 56 kbps achieve their rates by taking advantage of digital connections that circumvent some sources of noise in transmissions toward the end user. But these bit rates are far from the maximum possible on a twisted pair alone. One 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 Multi tone approach was intended for sending entertainment video over telephone wires. Because such use relies principally on one-way transmission, most of the sub channels 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 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 Wide Web 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 ADSL, 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 standard of ADSL is G lite which is just for home users, a global standard that limits the data rates to 1.5 Mbps downstream to the consumer and about 0.5 Mbps upstream. By limiting the speed G. lite is able to operate reliably on more than 70 percent of unaltered phone lines and lowers costs and power usage. Home computers containing G. lite-ready circuitry are already being sold.
ADSL has a number of advantages over systems that use a cable television network. With ADSL the signal on your line is not shared with other users. Where as cable modems are, which work over a giant network (party line) when someone else is receiving data, someone could be listening in on your data signal. Where as telephone wires, on the other hand, are physically secure. The backbone networks for ADSL carry composite signals for a few hundred consumers at 155 Mbps and up.
A television channel has an effective throughput of only about 24 Mbps, greatly limiting its effectiveness under heavy use by hundreds of cable modems. The ADSL traffic also benefits from a statistical economy of scale-for example, 1,550 people sharing a backbone of 155 Mbps will experience better performance than 240 sharing 24 Mbps. Although cable networks cover 90 percent of the homes in the U.S., they do not serve many businesses. Telephone networks are ubiquitous.
Moreover, for effective use of cable modems the cable operator must invest billions to upgrade the cable network with fiber optics and two-way transmission equipment; ADSL, on the other hand, takes advantage of the same kind of telephone pairs that Alexander Graham Bell used in the 19th century. Web Sites web web web.