title: How does a push server know where to send its notification to
body: <p>When I receive a notification on my phone, how was the push server able to communicate with the device?</p>
  
  <p>Is there a constant connection between client and server? As far as I know something like WebSockets will put a huge load on the server side with all these devices.</p>
  
  <p>Is it some kind of polling mechanism by the client? Seems still like a huge load of requests.</p>
  
  <p>Does the client keep the server up to date with his IP address? How comes no firewall blocks this request (like the one of the router when using Wifi)?</p>
  
  <p>Thanks!</p>