Reliable NAT traversal is what propelled Skype to fame and billions back in the day, and was later codified by the VoIP folks at the IETF into STUN/ICE and TURN

Reliable NAT traversal is what propelled Skype to fame and billions back in the day, and was later codified by the VoIP folks at the IETF into STUN/ICE and TURN. WebRTC is basically a VoIP client with JS API built into the browser.