ADSL

ADSL router with Wi-Fi (802.11 b-g)

D-Link DSL-10MF-NZ and DSL-11MF-NZ 20080103

Lantiq XWAY VRX288 V1.1

ADSL frequency plan

ADSL spectrum Fritz Box Fon WLAN

Asymmetric Digital Subscriber Line (ADSL) is a type of Digital Subscriber Line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL) by providing significantly faster download speeds than upload speeds. This is advantageous for typical home and small office internet access, where downloading information is much more common than uploading.

Overview

ADSL works by utilizing frequencies that are not used by a voice telephone call. A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service and voice calls at the same time. Data transmission rates can vary depending on the specific form of ADSL, the quality of the telephone line, and the distance from the distribution frame, typically located at the telephone company's central office.

Technology

The technology behind ADSL involves the division of the available bandwidth of a single telephone line into two or three frequency bands. The lowest band allows for telephone calls, while the higher bands handle upstream and downstream internet traffic. The division of bandwidth into separate channels allows for the simultaneous use of the phone line for voice calls and internet access.

ADSL Standards

Several standards define the specifics of ADSL technology, including:

• ANSI T1.413 – An early ADSL standard used primarily in North America.
• G.dmt (ITU-T Recommendation G.992.1) – A more widely adopted standard that includes support for "splitterless" ADSL, often referred to as "ADSL Lite."
• G.lite (ITU-T Recommendation G.992.2) – A simplified version of ADSL, without the need for splitters.
• ADSL2 (ITU-T Recommendation G.992.3) – Offers improved performance and longer reach compared to its predecessors.
• ADSL2+ (ITU-T Recommendation G.992.5) – Extends the bandwidth used for downstream data transmission, providing higher data rates.

Deployment

ADSL is widely used across the globe, with the highest penetration in regions where the infrastructure of copper telephone lines is extensive. Its deployment is often seen as a cost-effective way for telecommunications companies to provide high-speed internet access using existing telephone lines, avoiding the need for costly infrastructure upgrades.

Advantages and Disadvantages

The primary advantage of ADSL is its use of existing telephone lines, which allows for a relatively easy and inexpensive deployment by service providers. However, the quality and speed of ADSL service can be affected by the distance from the central office, with performance degrading the further the distance. Additionally, ADSL speeds, while suitable for many applications, may not meet the requirements of bandwidth-intensive activities.

Future of ADSL

With the advent of fiber-optic technology and the increasing demand for higher bandwidth, the role of ADSL is changing. Many service providers are gradually transitioning to Fiber to the Home (FTTH) or Fiber to the Cabinet (FTTC) technologies, which offer significantly higher speeds. However, ADSL remains a vital part of the internet access landscape, particularly in areas where the deployment of fiber is not yet economically viable.