RFC 2833 compatibility: telephone-event other than 8000 #10
Description
RFC 2833 is good, but in the real world it is a point where not followed by. Particularly, it breaks compatibility with some Asterisk versions, which support only telephone-event/8000. I expect many others PBX do not support other frequencies.
We have to find the way to save the compatibility and correspondence RFC 2833 both.
Probably, include telephone-event/8000 in case the other side not support other frequencies (so, include it anyway). And while sending DTMF, if it wasn't accepted, try sending it with 8000 again (but I'm not sure about the feedback presence here).