Using these settings, users can configure ring or tone frequencies
based on parameters from local telecom. By default, they are set to
North American standard.
Frequencies should be configured with known values to avoid
uncomfortable high pitch sounds.
Syntax: f1=val,f2=val[,c=on1/off1[-on2/off2[-on3/off3]]];
(Frequencies are in Hz and cadence on and off are in 10ms)
ON is the period of ringing (“On time” in ‘ms’) while OFF is the
period of silence. In order to set a continuous ring, OFF should be
zero. Otherwise it will ring ON ms and a pause of OFF ms and then
repeat the pattern. Up to three cadences are supported.