[Freeswitch-users] Identify billable calls

I am using bridge application to connect to carrier gateways and using CDR csv module for billing. In my logic I am only billing calls which have billsec>0 now I wonder if this is correct way to find what calls are connected I mean may be some calls I am ignoring which were connected for less than 1 second?..Is that possible?...what is the sure shot way to filter connected calls?