Hi guys, I have updates on this issue.
I got help from a guy who knows FreePBX far, far better than me, and he was able to lock down what he thinks is the route of the issue. He used tshark to log the incoming calls, and then we looked at the contents of the packets, and found that an incorrect header was being sent. The header looked like this:
Frame 10: 972 bytes on wire (7776 bits), 972 bytes captured (7776 bits) on interface 0
Ethernet II, Src: Microsof_69:5d:04 (00:15:5d:69:5d:04), Dst: 02:cf:02:40:d1:00 (02:cf:02:40:d1:00)
Internet Protocol Version 4, Src: 192.168.40.15, Dst: 188.8.131.52
User Datagram Protocol, Src Port: 5060, Dst Port: 5060
Session Initiation Protocol (PRACK)
Request-Line: PRACK sip:email@example.com:5060 SIP/2.0
[Expert Info (Warning/Undecoded): Trailing stray characters]
Via: SIP/2.0/UDP 192.168.40.15:5060;rport;branch=z9hG4bKPj3aa9898c-52f9-4d2f-9878-74413cba334f
From: “” sip:firstname.lastname@example.org;tag=10391aa7-0bb6-4727-87cf-69252d5a965c
[Generated Call-ID: d31f0b7e-cc8e-493f-8067-fec68cc04d04]
CSeq: 2979 PRACK
RAck: 486003279 2977 INVITE
That SIP header is obviously incorrect, and in the majority of the other instances of the PRACK, it was sent back correctly.
Thus, he concluded that this is most likely a bug within FreePBX. It is worth noting that I was using a pjsip trunk; he recommended I move to sip instead, as it is more mature and unlikely to have this issue. I will be doing so, and then monitoring over a few days to see if the issue goes away.
Is this a known issue within FreePBX? Is there a setting I can set within the pjsip trunk that will resolve this issue?