title: Reasons for asterisk HangupCause 'Unknown' and 'Normal Clearing'
body: <p>For some calls I am getting this HangupCause</p>
  
  <pre><code>X-Asterisk-HangupCause: Unknown.
  
  X-Asterisk-HangupCauseCode: 0.
  </code></pre>
  
  <p>And for some calls, getting this</p>
  
  <pre><code>X-Asterisk-HangupCause: Normal Clearing.
  
  X-Asterisk-HangupCauseCode: 16.
  </code></pre>
  
  <p>Have tried surfing but still having thoughts in mind.</p>
  
  <p>What are the reasons behind these <code>HangupCause</code>s?</p>