title: Chat application for Android using Firebase but without storing data in firebase
body: <p>We are developing one application using google classroom APIs where we are building relationship between teacher and student.</p>
  
  <p>Now, we need to add another feature which is basically one to one chat communication between Teacher and student. For this, I was thinking for XMPP or FCM. We have our own server implementation where users(Teachers and students) data are already present and maintained.</p>
  
  <p>But I have few questions on this:</p>
  
  <ol>
  <li>If I am going to use FCM based chat, do I need to authenticate the user against FCM? I am already using FCM for notification sending purpose.</li>
  <li>In some tutorials I have seen that, they are storing the conversations and user data in FCM database. Can I store them in my backend database without storing in FCM database.</li>
  <li>If i try with XMPP, I am getting many client side code and I can use smack API. But I am not understanding about the server side implementation. Is there any good tutorial or github link present?</li>
  </ol>
  
  <p>P.S. I am not going to use any existing chat sdk which has a pricing model. So, I need the suggestion based on the above.</p>
  
  <p>Thanks,
  Arindam.</p>