[Freeswitch-users] Unanswered pstn outbound call via gateway detection

Hi I have originated outbound call to pstn number using gateway provider flowroute with originate command. I am using python ESL to achieve this. If the call is not answered by pstn user, then i need to post status to my webserver . Can anyone suggests me how i can detect whether the pstn call is answered or not? Thanks Tanim