G.dmt is an ITU standard for ADSL that uses the multitone procedure, Discrete Multitone (DMT), as modulation.
The procedure, which is described in the ITU-T G.992.1 standard, extends the usable bandwidth over existing copper twisted pairs to 8 Mbit/sdownstream and 1.3 Mbit/s upstream.
The DMT method occupies between 2 and 15 bits per channel. If the transmission conditions change, then the modem can swap bits between different channels. If the bit swapping function is deactivated, then the modem must adapt to the changed transmission conditions.