Ringing (180) No SDP To Progress(183) With SDP Transition => No Audio.

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Dear List

I am testing various early audio scenarios with different voice IC’s, phones and pbxes.

In Switzerland, when you operate a value added number, you have to announce the price of the call, usually in early audio, before the call is established.

In ‘dialplan’ terms this would be:

exten => XX,1,Ringing exten => XX,n,Wait(15)
exten => XX,n,Progress exten => XX,n,Playback(price-announce,noanswer)
exten => XX,n,Wait(5)
exten => XX,n,Answer I see the asterisk playing the early announcement audio in the rtp stream. Some devices (arris EMTA) calling the asterisk also do play it to the caller.

But!

Most other devices I have tested just keep playing the locally generated ringtone despite getting an 183 with SDP and the announcement is never to be heard by the caller.

If I do to force inband ringback tone, this works with all devices I
have tested so far.

exten => XX,1,Progress exten => XX,n,Ringing exten => XX,n,Wait(15)
exten => XX,n,Playback(price-announce,noanswer)
exten => XX,n,Wait(5)
exten => XX,n,Answer

Is anything wrong with the transition of ringing without SDP (to have the local device generating ringback tone) and then start sending early audio with 183?

-BenoƮt Panizzon-

I m p r o W a r e A G – Leiter Commerce Kunden

One thought on - Ringing (180) No SDP To Progress(183) With SDP Transition => No Audio.

  • Both orderings of Ringing and Progress are valid. It is up to the calling device to handle it. As you have seen, there is quite a difference in how devices handle it. I have even seen where the calling device needs Ringing before Progress to handle the call correctly. I think that case was because the device was converting ISDN to SIP. I do think that the devices that don’t stop local ringback in favor of the incoming RTP stream following the 183 are broken. Unfortunately it is something that is out of your control.

    Richard