DSL: Digital Subscriber Line

DSL is fast and widely available, but it's not fastest, and still not widespread

By
Bradley Mitchell
Bradley Mitchell
Writer
  • Massachusetts Institute of Technology
  • University of Illinois
An MIT graduate who brings years of technical experience to articles on SEO, computers, and wireless networking.
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Updated on January 28, 2020

Digital Subscriber Line technology offers high-speed internet service for homes and businesses. It competes with cable and other forms of broadband internet. The technology behind DSL means your network and telephone service share the same phone line without disrupting either your voice or network connections.

DSL Speed

Illustration of a DSL and Cable store next to each other with posters extolling their services
 Lifewire / Jo Zixuan Xiuan

Basic DSL supports maximum download data rates ranging between 1.544 Mbps and 8.448 Mbps. Actual speeds vary in practice depending on the quality of the copper phone line installation involved and the length of the phone line needed to reach the service provider's premise equipment (sometimes generically called the central office).

Symmetric vs. Asymmetric DSL

Most types of DSL service are asymmetric—also known as ADSL. ADSL offers higher download speeds than upload speeds, a tradeoff that most residential providers make to better match the needs of typical households who generally do much more downloading. Symmetric DSL maintains equal data rates for both uploads and downloads.

Residential DSL Service

Well-known DSL providers in the United States include AT&T (U-Verse), Verizon, and Frontier Communications. Many smaller regional providers also offer DSL. Customers who subscribe to a DSL service plan pay a monthly or yearly subscription and must agree to the provider's terms of service. Most providers supply compatible DSL modem hardware to their customers if needed, although the hardware is generally available through retailers.

Business DSL Service

Besides its popularity in homes, many businesses also rely on DSL for their internet service. Business DSL differs from residential DSL in several key respects:

  • Symmetric DSL is typically used as businesses tend to generate higher volumes of outgoing traffic than a typical home.
  • Providers often sell higher tiers of service to their customers including higher data rate plans, premier customer support options, or bundling of other products.

Business-class DSL may be selected by landlords. Normally, residential-class DSL limits concurrent device access. For example, U-Verse technically doesn't allow more than four connections, and the more people or devices using a residential service, the slower the service for all users becomes.

Problems with DSL

DSL service only works over a limited physical distance and remains unavailable in many areas where the local telephone infrastructure does not support DSL technology.

Although DSL has been a mainstream type of internet service for many years, the experience of individual customers can vary greatly depending on the location, provider, quality of telephone wiring in their residence, and other technical factors.

As with other forms of internet service, the cost of DSL varies from region to region. An area with few providers may be more costly because of the lack of competition.

DSL does not perform nearly as fast as fiber internet connections. Some high-speed wireless options offer competitive speeds.

Because DSL lines use the same copper wire as wired telephone service, all wired phones in the home or business must use special filters that connect between the phone and the wall jack. If these filters aren't used, the DSL connection may be adversely affected.

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