ANSWEREDTIME and DIALEDTIME have the same value

Hi all,
How can I always get the same value for ANSWEREDTIME and DIALEDTIME?
They should have different values because the DIALEDTIME is the time from the caller starts dial the callee to end-conversation and the ANSWEREDTIME is the time from dial to answer. So the ANSWEREDTIME is always less than the DIALEDTIME. I have an asterisk IVR. When the callee picks up the phone, the IVR asks some questions before the call get connected. In my problem, the ANSWEREDTIME always equals the DIALEDTIME. I want to get the call-duration which is = DIALEDTIME - ANSWEREDTIME, but in my case it equals 0.
Did somebody experience this problem? please share a bit.