Next we have the ICE lines, which is the mechanism chosen for NAT traversal in WebRTC. You can find a very didactic and comprehensive explanation of ICE here. ICE is complex enough to deserve its own post, but I will try to explain its SDP lines in an understandable way.
Next we have the relay candidates. Those candidates are obtained from a TURN server which must be provisioned when creating the peer connection. Note that the priority here is lower than the host and reflex candidates (2157334355 is higher) so the relay will be used only if “hole punching” is not working with host and reflex candidates. Just for your curiosity we used the open source rfc5766-turn-server project in this test.