title: What is the primary usage of upstream messaging in GCM Cloud Connection Server?
body: <p>What is the usage of Cloud Connection Server that was announced at Google IO 2013?</p>
  
  <p>I'm interested to know whether I can use the upstream messaging feature to send specific messages to GCM server. For example, can I send a command to delete a GCM notification that is stored on the GCM server? Or is it only used to send custom messages? If so, why do we need it at all?</p>