GID&quot;
  }
  &lt;/gcm&gt;
&lt;/message&gt;</pre>

<p>Here is the format of the ACK expected by CCS from 3rd-party servers in response to the above message:</p>

<pre>&lt;message id=&quot;&quot;&gt;
  &lt;gcm xmlns=&quot;google:mobile:data&quot;&gt;
  {
      &quot;to&quot;:&quot;REGID&quot;,
      &quot;message_id&quot;:&quot;m-123&quot;
      &quot;message_type&quot;:&quot;ack&quot;
  }
  &lt;/gcm&gt;
&lt;/message&gt;</pre>


<h2 id="flow">Flow Control</h2>

<p>Every message sent to CCS receives either 