Asymmetric Digital Subscriber Line Details

Asymmetric Digital Subscriber Line (ADSL) is a fast internet connection great for achieving fast download speeds. As the name suggests, "asymmetric" stands for the fact that most of the two-way bandwidth is dedicated to downstream (data received) while only a small fraction is reserved for upstream (the speed of data sent). On average, this translates as 8Mbps downlink and about 640Kbps upload speeds. This is perfectly suitable for individuals and businesses' everyday general needs, like sending emails, posting on social media, browsing the internet, or downloading multi-media content if the client's needs require relatively little upstream traffic.

To work properly, a client needs to have an existing telephone landline. A technician needs to connect an ADSL modem to the line. A microfilter is used to separate the frequencies of the phone line reserved for voice transmission (200 Hz to 3,300 kHz) from the frequencies used for the broadband connection (above 4,000 kHz). A technique called discrete multitone (DMT) splits the bandwidth into 256 subchannels. This effectively allows data transmission by automatically measuring the signal to noise level as soon as the modem is turned on and allocates the data flow accordingly.

Naturally, ADSL has its limitations. Its speed largely depends on the quality of the existing infrastructure. The better your telephone cables, the better your speed. Fiber-optic cables, when available, are the preferred choice of many. Advances in wireless technology offer parallel connectivity speeds. However, coverage and pricing can be inhibiting factors. Considering all the advantages and limitations of ADSL, it remains one of the best value for money products regarding internet connectivity.

Real World Example of Asymmetric Digital Subscriber Line

Several telephone and internet providers offer ADSL, but the quality of their cables differs. For example, both Century and Frontier Internet use fiber cables. Verizon also offers DSL and broadband services. The company promotes this option as useful for those who want to use the internet and a landline simultaneously, prefer a modem, and don't want to share Wi-Fi with their neighbors.

History of Asymmetric Digital Subscriber Line

ADSL can thank its conception to telecommunication companies wanting to enter the cable-television market in the early 1990s. ADSL technology takes advantage of the fact that traditional copper telephone lines use only about 0.3% of the total bandwidth to transfer voice across the network.

Considering the extensiveness of the traditional telephone network infrastructure built up over the years, it comes as little surprise that telecom companies sought to use the remaining frequencies. The original intention was to offer video-on-demand services. But due to the immaturity of the market and the increasing pressure to compete with cable-TV companies offering fast internet connections, ADSL was launched as a product offering broadband internet solutions making use of the client's existing landline.

The technology proved to be so popular and successful that it took just over a decade for ADSL to move from a conceptual phase to a widely available commercial product.

ADSL vs DSL

ADSL is just one of many types of digital subscriber line (DSL) connections. DSL is simply a digital connection made through both a phone line and a modem. DSL uses the unused wires in a telephone to function.