How does the TURN server interact with other components if two clients are behind NaTs?
This is the primary purpose of the TURN server (when at least one client cannot form a direct connection because of a restrictive NAT). Direct P2P connections will be relayed through the TURN server. So this includes calls (voice and video) and file transfers. Whichever client is using the TURN server will send the TURN server’s IP address to their contact instead of their own IP address.
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On the subject of STUN and TURN servers, i found a high-level explanation done by Rob Braxman on odysee.com (odysee relies on LBRY, a bittorrent-ish like video sharing platform)