Playback through zap channel


I am using Asterisk-1.4.2.

I am trying to make asterisk auto-dial an external number. Basically, I want Asterisk to dial a number and play an announcment as soon as the callee pics up.

With SIP phones, everything works fine, but with Zap channel, I was encountering the problem, that Asterisk would detect the Answer event as soon as the connection was made(and not wait for the callee to pick up the phone, as it does in the case of SIP phone).

I figured out that using c option in Dial would solve my problem. So, now Asterisk detects the Answer event, after the callee has picked up the phone, and pressed the pound(#) key.

The command I am using is

exten => 502,n,Dial(Zap/2c/9795190920#,gM(try),)

However, I do not want that the callee press the pound key, Instead, I want Asterisk to automatically play an annoucement as soon as the callee picks up the phone,( waiting for the callee to press the pound key is very inconvenient).i.e I want Asterisk to detect the answer event, without the pound key being pressed.

How can I possibly do this?

Thanks for the help

1.4.2 is obsolete.

You need your network operator to provide answer supervision and you need an FXO card that supports it, and is configured to do so.

The most common form is probably line polarity reversal.

Thanks for your reply, I tried polarity reversal and now asterisk does’nt detect the answer event as soon as the zap connection was made, that’s ok, but the problem is that asterisk does’nt detect the answer event event if the calle pick up the phone.
So how can i solve that issue. Also can you explain what answer supervision is .

Thanks for your help

Get your network provider to provide line reversal answer supervision.

(There are probably ways using tone and speech detection algorithms, but getting proper answer supervision is going to be the easiest if you have a proper business phone line.)