title: How does server locate GCM (Google Cloud Messaging) registration IDs
body: <p>I am trying to write an application which notifies a cellphone using GCM. I was able to implement basic functionality, but there is one question I'm still unsure of</p>
  
  <p>As I understand, the flow goes like this:</p>
  
  <ol>
  <li>Device start up</li>
  <li>Device registers, obtains registration id</li>
  <li>Server gets the knowledge of registration id on device</li>
  <li>Server is using it's API key + registration id to send payload to device</li>
  <li>Device receives payload.</li>
  </ol>
  
  <p>One thing which is unclear to me is: what is a proper methodology to implement step #3?</p>
  
  <p>I could not find any way to obtain a list of registered devices. Lets imagine, I am using GCM for a purpose of posting to a known device, and I could email that ID to myself and then register it on the server manually. But as I understand, it expires.</p>
  
  <p>So, it there an expectation that I have to keep re-registering and somehow notifying server every time it happens?</p>