ADSL - Asymmetric Digital Subscriber Line

ADSL is a type of Digital Subscriber Line (DSL) Internet service commonly used in homes. The 'A' in ADSL refers to the unequal distribution network bandwidth between downloads and uploads: ADSL connections provide comparatively more bandwidth for downloads than for uploads. ADSL is designed to support the typical home user who frequently downloads large amounts of data from Web sites and online networks but uploads relatively less often. ADSL works by allocating a majority of the available phone line frequencies for communication of downstream traffic. In other respects, ADSL possesses all of the characteristics one associates with DSL, including high-speed service, an "always on" combination of voice and data support, and availability and performance that is limited by physical distance.
ADSL allows more data to be sent over existing copper telephone lines (POTS), when compared to traditional modem lines. A special filter, called a microfilter, is installed on a subscriber's telephone line to allow both ADSL and regular voice (telephone) services to be used at the same time. ADSL requires a special ADSL modem and subscribers must be in close geographical locations to the provider's central office to receive ADSL service. Typically this distance is within a radius of 2 to 2.5 miles. ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).

What Are the Different Types of DSL Technology?

All types of DSL Internet service can be categorized as either asymmetric or symmetric.
 
In a symmetric computer network, all devices can transmit and receive data at equal rates. Asymmetric networks, on the other hand, support disproportianately more bandwidth in one direction than the other. Digital Subscriber Line (DSL) technology exists in both symmetric and asymmetric forms. Asymmetric DSL (ADSL) offers much more bandwidth for downloads by sacrificing bandwidth available for uploads. Conversely, symmetric DSL (SDSL) supports equal bandwidth in both directions. Internet services for home normally provide ADSL as typical Internet users tend to download much more data than they upload. Business networks more commonly use SDSL. Besides DSL networking, the terms "symmetry" and "asymmetry" also apply to network design in more general ways.

Asymmetric DSL

Asymmetric types of DSL connections provide more network bandwidth for downloading (from the Internet service provider down to the subscriber's computer) than for uploading in the other direction). By reducing the amount of bandwidth available upstream, service providers are able to offer relatively more bandwidth downstream.

Asymmetric DSL technology is popular in residential DSL services as home Internet users predominately use downstream bandwidth. Typical asymmetric DSL services support 5 Mbps for downloads and 1 Mbps for uploads.

Common forms of asymmetric DSL include:

ADSL (and G.Lite)
RADSL
VDSL

Symmetric DSL

Symmetric types of DSL connections provide equal bandwidth for both uploads and downloads.

DSL - Digital Subscriber Line

 DSL is a high-speed Internet service like cable Internet. DSL provides high-speed networking over ordinary phone lines using broadband modem technology. DSL technology allows Internet and telephone service to work over the same phone line without requiring customers to disconnect either their voice or Internet connections.

DSL technology theoretically supports data rates of 8.448 Mbps, although typical rates are 1.544 Mbps or lower.

DSL Internet services are used primarily in homes and small businesses. DSL Internet service only works over a limited physical distance and remains unavailable in many areas where the local telephone infrastructure does not support DSL technology.

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