'Telephone-event' in RTP Payload
Hi,
I've been doing a lot of voice call troubleshooting lately, in particular in the RTP Streams and RTP Stream Analysis areas.
I have found that some calls have 'telephone-event' listed alongside the codec in the payload. (Sorry, I don't have enough points to upload a screenshot of this).
I have also noticed that I can't export the audio stream if the 'telephone-event' is present. When I try, I get the error' Codec is not supported, file is incomplete'. As far as I'm aware my files are not missing anything. If the telephone-event label is not present, I have no difficulties exporting the audio.
I would like to understand what the telephone-event in the payload means. I've tried searching, but I haven't found anything yet. Can anyone help me out?
Thanks
Comments
I think I have worked out part of the issue. Seems pretty obvious now.
The telephone-event is DTMF. That is, 'press 1 for service...' or something like that. When I looked at the flow sequence, I could clearly see 'RTP (telephone-event) DTMF One 1' as part of the flow.
Now to figure out why I can't export the audio...
Ok, Here's the next part. Hopefully it helps someone out.
Any time in-band DTMF is used, I can't export the audio to a file. I've found out how to resolve that. If we want to, we can filter for RTP events like DTMF using
rtpeventSo, all we need to do is filter these our before exporting, using
!rtpeventWhen they're filtered out, we can then export the audio to an .au file.Seems like this could be handled better but will leave to more experienced people to explain.
It can be recreated using SIP_DTMF2.cap from the Wiki Sample Captures