In early phases DSL was most commonly known as digital subscribers loop but since it has gained lots of popularity it is now known as digital subscribers line. The basic function of DSL is that it provides digital data to pass through the lines of telephone. DSL has this unique property that it can be used with the telephone line without disturbing it. This unique property is due to the fact that DSL usually uses very high frequency while the ordinary telephone operates at a low frequency as compared with the DSL. The performance of DSL depends upon two things:

1. What service level is adopted?
2. What is the condition of line?

The working of DSL is basically in two very simple steps. DSL divides the frequencies that are used in a telephone in to two parts. First is the ISP data which is carried through the higher frequency and the second which is most important is the voice which is carried over through the low frequency. This is the only reason the DSL modem and the telephone lines can be used together. The basic working of the DSL is as follows:

  • First of all DSL modem is attached to the customer’s phone line.
  • Now the telephone company connects the other part of the telephone line to what is called as DSLAM.
  • When the DSL modem is switched on it does a self test.
  • It normally checks the connection between the DSL modem and the sender.
  • In the last phase the DSL modem tries to synchronize with the DSLAM.

The basic function of the DSL modem is that it converts the digital data into small voltage signals that can be used in the phone lines. In very few cases some DSL do require some sort of filters to be installed. These filters are installed at the telephones near the customer residence. There are lots of digital subscribers technologies like:

  1. ISDN
  2. HDSL
  3. SDSL
  4. ADSL
  5. ADSL2
  6. ADSL++

DSL carries a download speed from around 256kbit/s to almost around 28000kbit/s and it varies.DSL is the latest technology that is being used for high speed connectivity and optimum performance.