DSL

The DSL (Digital Subscriber Line) technology allowed the fast growth of the Internet and popularisation of on-line services. The classic modem connection (dial-up Internet access) provides the 56 kbps speed. It also blocks the voice calls, so you cannot browse the Internet or call at the same time. At the beginning, the DSL technology has provided the Internet links with throughputs between 1 Mbps and 2 Mbps. Therefore, this solution was 20 times faster than the classic modem connection. The DSL uses the higher frequencies than the POTS (Plain Old Telephone Service), i.e. voice calls, so it is possible to use the Internet and to call at the same time.

This Internet access solution is very well thought out. It uses the normal telephone line, so the provider does not have to install any new cables. This ensured the success and popularity of the DSL technology. In order to use the Internet and the analogue phone at the same, it is required to install special filter which separates the digital data form the call.

The modern versions of the DSL technology provide aggregated speeds up to 250 Mbps, because it uses much wider bandwidth and advanced modulation and coding techniques. However, higher throughput requires also better quality cables and shorter distances.

The DSL is one of the most popular Internet access technique and it is estimated that this is the dominant technology for broadband access with over 360 million subscribers worldwide. This is the reason why the DSL is constantly being improved and a lot variants of the DSL technology was developed over the years. However, the most popular implementations are ADSL (Asymmetric Digital Subscriber Line) and VDSL (Very-high-bit-rate Digital Subscriber Line).

Advantages of DSL :

  • Here are some advantages of DSL:
  • The speed is much higher than a regular modem
  • DSL doesn't necessarily require new wiring; it can use the phone line you already have.
  • DSL doesn't necessarily require new wiring; it can use the phone line you already have.

But there are disadvantages :

  • A DSL connection works better when you are closer to the provider's central office. The farther away you get from the central office, the weaker the signal becomes.
  • The connection is faster for receiving data than it is for sending data over the Internet.
  • The service is not available everywhere.

In this article, we explain how a DSL connection manages to squeeze more information through a standard phone line -- and lets you make regular telephone calls even when you're online.

Telephone Lines

If you have read How Telephones Work, then you know that a standard telephone installation in the United States consists of a pair of copper wires that the phone company installs in your home. The copper wires have lots of room for carrying more than your phone conversations -- they are capable of handling a much greater bandwidth, or range of frequencies, than that demanded for voice. DSL exploits this "extra capacity" to carry information on the wire without disturbing the line's ability to carry conversations. The entire plan is based on matching particular frequencies to specific tasks.

To understand DSL, you first need to know a couple of things about a normal telephone line -- the kind that telephone professionals call POTS, for Plain Old Telephone Service. One of the ways that POTS makes the most of the telephone company's wires and equipment is by limiting the frequencies that the switches, telephones and other equipment will carry. Human voices, speaking in normal conversational tones, can be carried in a frequency range of 0 to 3,400 Hertz (cycles per second -- see How Telephones Work for a great demonstration of this). This range of frequencies is tiny. For example, compare this to the range of most stereo speakers, which cover from roughly 20 Hertz to 20,000 Hertz. And the wires themselves have the potential to handle frequencies up to several million Hertz in most cases. ­

The use of such a small portion of the wire's total bandwidth is historical -- remember that the telephone system has been in place, using a pair of copper wires to each home, for about a century. By limiting the frequencies carried over the lines, the telephone ­system can pack lots of wires into a very small space without worrying about interference between lines. Modern equipment that sends digital rather than analog data can safely use much more of the telephone line's capacity. DSL does just that.

A DSL internet connection is one of many effective communication tools for keeping employees in touch with the office.