ADSL Essay Research Paper Overview

ADSL Essay, Research Paper

Overview

Asymmetrical Digital Subscriber Line

(ADSL) uses the plain twisted pair wiring already carrying phone service

to subscribers’ homes to transmit video signals and high-speed data

to the home. ADSL uses adaptive digital filtering to overcome noise and

other problems on the line. Initially, the telephone companies hoped to

use ADSL to provide Video on Demand service in competition with cable

pay-per-view and neighborhood video rental stores. But ADSL can also offer

a wide range of other applications, including Internet service, work-at-home

access to corporations, and interactive services, such as home shopping

and home banking. In addition, ADSL could make at-home educational access

affordable for consumers.

Early Development

As early as 1991, Bellcore, the

research company associated with the seven regional Bell operating companies,

began touting ADSL to expand the transmission capacity of the copper-based

telephone networks. This was originally seen as the telephone companies’

answer to CATV’s encroachment into telephone service and their entree

into providing video on demand to telephone customers. Both the cable

companies and the telephone companies were itching to get into each other’s

businesses, but their networks were totally different, each with its own

strong points and shortcomings. The telephone companies had greater access

to homes in the United States (more than 90 percent), but the cable companies

had more bandwidth capacity going into homes. The telephone companies

were set up for two-way communication, but lost video quality over distance.

The cable companies had better quality but limited upstream capacity.

Both industries knew that their ultimate solution would be fiber-optic

networks connecting everyone, but realistically this was not possible.

Although fiber has been run by both cable companies and telcos over the

vast majority of their network, taking it from the curb to the customer’s

residence or business was the problem. The cost alone would run into the

billions, and nobody could afford to keep laying fiber in hopes that the

home they went to would use all of the capabilities fiber had to offer.

Enter ADSL. ADSL allows a standard copper telephone line to carry a high-speed

digital signal while simultaneously transmitting a voice conversation.

The asymmetrical part of the service refers to the fact that the high-speed

transmission of data is one-way, from the central office to the home or

business. Since most homes or small businesses only need the speed to

receive information, not transmit it, this works very well. And, initially,

ADSL permitted transmission at 1.5 megabits per second (Mbps) over copper

wire for up to 18,000 feet. The vast majority of small businesses and

residences easily fell within 18,000 feet of a telephone switching office.

Because of the poor initial success of the last great plan to use the

telephone companies’ copper wire, Integrated Services Digital Networks

(ISDN), ADSL was met with skepticism. Many telcos, as well as manufacturers,

originally developed a wait-and-see attitude before investing in the new

service. But, in 1993, a tiny California company called Amati

teamed up with Northern Telecom

to prove that ADSL could be used to send 6 Mbps of full-motion video down

a conventional telephone line. Suddenly the telephone companies had a

weapon, albeit an interim one, that could be used against the cable companies.

Big companies, like Bell Atlantic,

realized that ADSL could be used immediately to stay in the game, removing

the pressure to replace the copper wire with fiber. Instead of spending

time and money to bring hybrid fiber/coax (HFC) or fiber-to-the-curb (FTTC)

into a large area for an unknown number of users, the telcos could now

target specific users who were willing to pay for the equipment necessary

to make the service work.

ADSL Today

By 1994, ADSL development provided for 7 Mbps of downstream bandwidth

and up to 576 kbps of return bandwidth. This enabled the telcos to use

the copper wire paths to offer basic telephone service, ISDN, full-motion

video, and videoconferencing. AT&T

began its own development process using a carrierless amplitude and

phase (CAP) modulation alternative to the discrete multitone (DMT) developed

by Amati for ADSL. Although DMT appeared to be the best of the two alternatives,

CAP was available more quickly. Eventually, it was clear that either alternative

could be used by an operating company, they just couldn’t’t be mixed

in the same system.

The first trials of ADSL were relatively simple. There was a box at each

end of a conventional telephone line, that is, one in the customer’s

home/business and one in the phone company’s switching office. The

box

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