[milankragujevic]

Yes, signaling is definitely centralized, before it was done by mega-peers. P2P contact does work behind NAT if it's a cone NAT. Symmetric NAT would require that the signaling server assign a forwarding server to handle data from and to each peer. In general CGNAT applications with cone NAT, UDP hole punching can be used to communicate between peers, organized by the signaling server.