title: How to achieve callbacks in WCF service?
body: <p>I have to create a WCF service that handles following tasks:</p>
  
  <ol>
  <li>Register the notification sent from multiple client through WCF service.</li>
  <li>The WCF service in turn sends ( Callback) the notification to the multiple client.</li>
  </ol>
  
  <p>The WCF service also want to listen a datachange notification from another database server.</p>
  
  <p>Can a WCF service is treated as a Listener that listen and send notifications for each request.</p>