There's no TURN server set for this, but it shouldn't be hard to add one. There are NATs where you'd need one to relay all the traffic, but these seem to be relatively rare nowadays. If anyone has any actual statistics on these I'd appreciate it!
AT&T 5G uses Symmetric NAT. It's not rare if you have an iPhone or iPad with cellular. No way to do P2P without relaying traffic unless you want to "guess" the randomized port number, and, on that front, there are NAT-device-aware algorithms that can make that process faster.
We were promised IPv6 will make NAT's not necessary but I believe service providers use NATs not simply to conserve the IPv4 space but to actively discourage using the service to host your own servers.
They are zealously pushing the "ever increasing speeds" of questionable benefit for the user - what for? So that commuters could watch 8k 120fps video while on a bus? Or rather to gather all kind of sensor data in real-time, audio and video included, from their human oil wells? To strip off people's clothes with millimetre wave imaging?
But making it easy for people to run their own home/mobile servers, share and cooperate without govporate oversight is clearly not on their agenda.
Source: https://github.com/saljam/webwormhole/blob/8f707583d68173de3...
On command line it's an option and Google's is default. I'd like to make the signalling server also a STUN server at some point.
But way back in 2014 a Google employee does seem to have confirmed it's free to use, but comes without guarantees.
[1] https://groups.google.com/d/msg/discuss-webrtc/shcPIaPxwo8/F...