This is what I am getting from NexVortex.
The issue at hand remains the SDP offering from the Cisco. I looked at the last outbound attempt, and it is still sending an invalid media mapping via the m= header. See the example below:
2022-11-22 12:54:25 -0500 : 147.0.29.51:5060 -> 104.219.163.73:5060
INVITE sip:xxxxxxxxxx@nexvortex.com:5060;transport=UDP SIP/2.0
Contact: "Fax #2"<sip:xxxxxxxxxxx@XXX.xx.xx.xx:5060;transport=UDP>
To: <sip:xxxxxxxxxx@nexvortex.com>
From: "Fax #2"<sip:xxxxxxxxxxx@xxx.xx.xx.xx:5060>;tag=0_3705435581-798620795
Call-ID: 3705434516-798620793X
CSeq: 1 INVITE
Session-Expires: 90;Refresher=uas
Min-SE: 90
User-Agent: Mitel-3300-ICP 20.4.1.34 Mitel Border GW(MBG/11.4.0.247 TUG/4.15.0.155-01)
P-Asserted-Identity: "Fax #2"<sip:xxxxxxxxxxx@xxx.xx.xx.xx:5060;transport=UDP>
v=0
o=- 6437 6437 IN IP4 xxx.xx.xx.xx
s=NSTREAMING
c=IN IP4 xxx.xx.xx.xx
t=0 0
m=audio 20212 RTP/AVP 0 8 18 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
m=image 0 udptl 0
a=rtpmap:0 PCMU/8000
m=image 0 udptl 0 is not a valid media mapping supported by any of the upstream carriers networks we have tried to route to.
It doesn't appear to be valid per the RFC either. Can you send calls without this image codec mapping?