DISA and g729


When i try to use DISA function with codec g729, it does not work, i think it’s because the second dial tone is recorded in other codec format and Asterisk can’t translate it in g729 because there is no license for g729.

How it the second dial tone generated ?
is it a file that we can add in g729 format or the tone is generated by the processor ?

Thanks for your help