difference between ${CDR(duration)} and ${CDR(billsec)} in asterisk dialplan

Question

I want to get the duration of the call but confused which variable to use

${CDR(duration)} or

${CDR(billsec)}

Here it is not clear from when ${CDR(duration)} records the time

So which should i use ${CDR(duration)} or ${CDR(billsec)} ?

Answer 1

Let say call come in and no answer for X second, after that answered, after that Y seconds speaks/play something and hang up.

So duration will be X + Y, while billsec(time to be billed) will be Y.

CDR(billsec) is answered time or time to be billed, without call setup time(post-dial delay).