I have never been able to get UDP transport to work on these devices behind NAT. It is always my protocol choice due to the fact that it gets around most router issues. I am curious, has anyone been successful getting UDP behind a single NAT to work (with or without STUN)?


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TCP usually works far more reliably than UDP. They key with those things, if they are the same as SPA phones is in the advanced sip settings to enable "insert via rport" and "handle via rport".
I didn't have access to make network/router changes so I had to support UDP to get around that limitation.

I heavily use the ATA for faxing and both UDP and TCP are working really well with the mod_spandsp based t38 gateway. I would like to use TLS on these Cisco ATAs but it looks like you have to get a signed cert from Cisco to support this. I am also very concerned about the lack of HTTPS/TLS support for provisioning as this is a big red flag for me.

Really appreciated the insight.