title: Send message from Server to Android device and vice versa
body: <p>I want to implement a chat application. But I have a few questions, which I could not solve by searching the internet.</p>
  
  <p>My requests are:</p>
  
  <ul>
  <li>Of course I can address each device individually from my server (makes sense for a chat app)</li>
  <li>I can create a time delay between sending and receiving a message</li>
  <li>The application should not require a registration (this is not a MUST, but would be nice)</li>
  </ul>
  
  <p>I wonder if GCM (Google Cloud Messaging) is the appropriate solution for me. I have not yet worked with it, so I would like to have some help. Will I run into troubles with this? And most important: Is a registration required?</p>