what is ADSL Concept, Features, Advantages and Disadvantages

What is ADSL?

We explain what ADSL is and the basics of this technology. In addition, what it is used for, its characteristics, advantages and disadvantages.

The ADSL serves as a digital data transmission channel and Internet connection.what is ADSL

ADSL (Asymmetric Digital Subscriber List) is a type of digital data transmission and Internet access technology consisting of transmission over symmetric copper telephone line pairs.

This is a method of Internet access through the telephone line (Switched Telephone Network, PSTN) that does not prevent regular use of the line for calls.

ADSL is a type of Broadband connection, whose name comes from the fact that the download (from the network to the computer) and upload (from the computer to the network) capacity are not coincident, but that the former is greater than the latter. After all, most Internet users receive more information than they broadcast.

For ADSL to work, it is necessary to have a telephone line and a modulation system that separates frequencies from voice and data, through the installation of discriminating filters (called splitters, microfilters or DSL filters) and an ADSL router provided by the company that provides the service.

This type of urban copper cabling was traditionally implemented, but in the late decades of the twentieth century were gradually replaced by fiberglass, a material that offered better conduction and performance, thus accommodating even better methods of transmitting digital information, such as cable modem or Ethernet.

What is ADSL for?

Like other digital transmission systems, ADSL serves as a digital data transmission channel and Internet connection.

This means that it is a virtually unlimited source of information and online services, with all that that implies. This method of connection was key in the massification of the Internet in homes and urban environments during the 1990s.

Characteristics of ADSL

In an ADSL connection, three independent transmission lines are established:

  1. Data transmission channel. Where the user’s information will be sent to the Internet (upload).
  2. Data reception channel. Where the information will be received from the Internet (download). It will be the widest of the three channels.
  3. Regular telephone service channel. Where the telephone calls will be transmitted.

This separation allows a differentiated handling of data and transmission impulses, and can even be improved in the versions known as ADSL2 and ADSL2+, which also receives a channel for the transmission of subscription television (cable TV) and high quality video (HD).

Advantages of ADSL

Each subscriber receives an independent and non-transferable service directly to their home.

It doesn’t occupy the telephone line. This represents an advantage when installing the service in homes and companies, as it allows the autonomy of both services, something impossible with the dialing method.

It employs traditional infrastructure. It does not require new and extensive investments or major works, as it takes advantage of traditional copper cabling.

Outperforms dial-up connection. It offers a much better speed/price ratio than dialing methods, which in addition to occupying the telephone line usually go to 56 kps, while ADSL can reach 4mbps (70 times faster).

Allows central and customized circuits. Because it uses telephone cables, each subscriber receives an independent, non-transferable service directly to their home or office.

Disadvantages of ADSL

  • It doesn’t operate on every phone line. It is not enough to have a telephone connection by copper cabling to use ADSL, as this technology has a limit of 3km of line length from the central transmitter.
  • It demands copper quality. In countries where this material is expensive or scarce the service may not be as inexpensive as in others.
  • It depends on external factors. The quality of the service is subject to the quality of the cables, the distance from the plant and fluctuations in the flow of the service.
  • It’s far inferior to fiber optics. Fiber optic connections far outperform ADSL in stability and speed.


The VDSL or VHDSL (Very High-bit-rate Digital Subscriber Line) is a type of broadband Internet connection with a much higher performance than ADSL, representing its evolution or superior step.

This technology consists of the use of four channels for data transmission: two for unloading and two for loading, substantially increasing the transmission power of the service.

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