10.61.3. Generation (Example) 
ADD-ACTDA:TYPE=STN,STNO=37278,FEATCD=VARRING, RNGTIME=10;
The ring time in seconds can also set via the service
menu (not valid fro Anate) at the device itself:
Service Menue > Destinations > Call Forwarding > FWD-VAR-RNA-BOTH > Ringing
duration until forwarding
Enter the number of seconds and safe your new settings.