Hi all

I have a question regarding Call Progress Monitoring. I've seen several ICs
that perform this function, but don't quite understand how they determine
call stages that don't have "TONES", like when the call is ANSWERED, and when
it is disconnected.

For example, do I simply watch for the "ringing" state to end, and assume that
means the call was answered? zarlink DAA and DTMF chips gives such output means one pin gives the frequency of dialing progress. I am confused with how to detect that the call is answered. one way is to watch the dialing frequency and when it is finished for some time then i can assume that the call has been answered and i can play the stored message for the receiver. if this is true there are are two considerations.

- how long should i wait to decide that the call is answered by watching the rininging frequnecy specially when the eruipment is to be used in differenct countries with possibly varying dial tone frequencies. like rrrrr.....rrrrr......rrrrr or rrrrrrrr...rrrrrrrr...rrrrrrrr or rrrr.......rrrr.........rrrr


- is it not possible that when my microcontroller is in the wait state to decide that the call is been answered.. the receiver will terminate the call because he think there is no one to speak.

So i want a very clean methods to detect that the call has been answered or hangup



I am using Zarlink MH88422 as DAA and 8880

thanks
Shahzad Aslam