Hi there,
This is newly found that with all udp traffic filtered, SIP phone application doesn't have audio anymore.
With wireshark analysis, it seems that STUN protocol gets upset in advance of RTP messages. It turns into some unknown format although we only pipe it through. Only way to workaround is to bypass all rtp ports. But we cannot do that as it is a huge range.
Thanks in advance for any suggestion.
Attached the case with/without rtp range bypassed. That was tested with linphone SIP phone application.