ADSL is a technology developed to be able to pass computer data through telephone lines.
The high frequency bands of ADSL are those not used by the telephone (300 - 3400 Hz), multiplexing and modulation techniques are implemented.
However, using the high frequencies of the telephone line implies the use of a filter on both sides of the line so that there is no disturbance.
The streams are asymmetric, which means that in ADSL, a subscriber can send data (uplink) at a lower rate than it can receive (downlink).
ADSL has made it possible to obtain speeds 10 to 500 times higher than previous Internet access techniques, thus offering providers the possibility of offering services other than Internet access, as is the case with Triple-Play offers.
Subscribers whose telephone line is not unbundled can, at best, only benefit from a speed of 2 Mbps, which is not enough to pass audio/video streams.
The speeds proposed by ADSL are ideal rates, because ADSL is very sensitive to the attenuation of telephone lines.
Thus, the longer a line will be between a subscriber and his telephone exchange, the less the speed he will be able to obtain via ADSL will be. Similarly if the line is damaged, or if it has electronic devices.