If you have the means to pull a trace you might want to check to see if the sender is using the UPDATE with SDP method as a keep alive. I ran into this recently. It was causing faxes to our fax server to dump after 3 min (which was the session timer). Fixed it by tweaking the SBC to retranslate the UPDATE message as a re-invite. I've fought FOIP issues for about the last ten years. Seems like you'll get a good signalling scheme in place then some DSU (Dipshit user) who insists that it has to be your problem because their proctologists office that is trying to send the test results says so. The fact that you can send and receive to 99.999 percent of the would means nothing to this "expert". Voice band data devices need to go extinct.
END OF RANT.

Last edited by aswipay; 02/20/20 05:52 PM.