title: how listening to a socket works
body: <p>If a client listens on a socket, at <a href="http://socketplaceonnet.com" rel="noreferrer">http://socketplaceonnet.com</a> for example, how does it know that there is new content? I assume the server cannot send data directly to the client, as the client could be behind a router, with no port forwarding so a direct connection is not possible. The client could be a mobile phone which changes it's IP address. I understand that for the client to be a listener, the server doesn't need to know the client's IP.</p>
  
  <p>Thank you</p>