ADSL (Asymmetric Digital Subscriber Line)

ADSL transmit high bit rate data in the forward direction to the subscriber, and lower bit rate data in the reverse direction to the central office, both on a single copper telephone loop. ADSL standards use discrete multi-tone (DMT) modulation [2]. DMT divides the
effectively bandlimited communication channel into a larger number of orthogonal narrowband subchannels. This allows for maximizing the transmitted bit rate and adapting to changing line conditions.

The analog information can be a standard POTS or ISDN signal. The maximum downstream digital transmission rate (data rate to the end user) can vary from 1.5 Mbps to 9 Mbps downstream and the maximum upstream digital transmission rate (from the customer to the network) varies from 16 kbps to approximately 800 kbps. The data transmission rate varies depending on distance, line distortion and settings from the ADSL service provider.

A block diagram for data transmission on an ADSL transceiver as below: