title: How GCM detects various devices with same app
body: <p>I am working on an android app and wants to use <code>GCM</code>. I have read about GCM from various blogs but i am not getting how GCM detects different devices. I know there is <code>registration id returned by the GCM server but we are sending project number as sender's id , then how GCM detects various android devices with that app</code>. Is there any MAC or IMEI number goes along with the sender's id or what?</p>
  
  <p>Any suggestion would be helpful......</p>