title: Is STUN server absolutely necessary for webrtc when I have a socket.io based signaling server?
body: <p>My understanding about STUN server for webrtc is that when the clients are behind the NAT (in most cases, if not all), the STUN server will help the webrtc clients to identify their addresses and ports. And I also read some article saying that a signaling server is needed for webrtc clients. The signaling server could be a web server, socket.io, or even emailing a url. My first question would be: is the STUN server the signaling server?</p>
  
  <p>Actually now I built a very simple socket.io based service which broadcasts client's session descriptions to all other clients. So I believe the socket.io based server should have enough knowledge about the clients' addresses and ports information. If this is the case, why do we bother to have another STUN server?</p>