Hello, Pix! Our activities is not stoped even in the weekend:)
Start DTMF message is initiated by depression of a key button in mobile phone in speech call. Stop DTMF message is initiated by release key button in the phone. Start DTMF message contains the digit value (0-9,*-A,#-B). A digit value corresponds a certain combination of frequency pair:
for example, 1= 697Hz+1209Hz,#=941Hz+1477Hz etc. The digit value from Start DTMF message is converted in MSC to dual frequency signal and sent on traffic channel. And so on. Also Start-Stop message may be transfered automatically within timing restriction for DTMF (70 ms – tone, 65 ms – pause). See also 23.014 about DTMF in PLMN.