So I finally could find a fix. Then problem is the ring_on and ring_off length as defined by wp_globals in ozmod_wanpipe.c For France (and I guess all other European countries), the ring on and off length shall be 1700ms and 3300ms. That correspond (at least for Europe) to the length of the ringing tone. So I was wondering I it would not be a good idea to take these values from the tones.conf file. I wonder if that is possible in wp_open_range function in ozmod_wanpipe.c. Could anybody indicate if there is any diagram of how each module in openzap calls the other, then that could be a good starting point (I dont really get the interactions/calls between ozmod_wanpipe.c and ozmod_analog.c). Also, I would need to know if this tone generation should apply to span types other than FXS. Thanks François