title: How to use notification_key using GCM?
body: <p>Is there any GCM client and server php example which describes use of notification_key .Since my application needs push notification for user with multiple devices. But couldnot find any suitable example or way to implement this <a href="http://developer.android.com/google/gcm/notifications.html" rel="nofollow">http://developer.android.com/google/gcm/notifications.html</a>.</p>
  
  <p>Thanks,Please help.</p>