title: How does a WCF server inform a WCF client about changes? (Better solution then simple polling, e.g. Comet or long polling)
body: <blockquote>
    <p>see also "<a href="https://stackoverflow.com/questions/22340/wcf-push-to-client-through-firewall">WCF push to client through
    firewall</a>"</p>
  </blockquote>
  
  <p>I need to have a WCF client that connect to a WCF server, then when some of the data <strong>changes</strong> on the server the clients need to <strong>update</strong> its display.</p>
  
  <p>As there is likely to be a firewall between the clients and the server.</p>
  
  <ul>
  <li>All communications must be over HTTP</li>
  <li><strong>The server can not make an (physical) outgoing call to the client.</strong></li>
  </ul>
  
  <p><em>As I am writing both the client and the server I do not need to limit the solution to only using soap etc.</em></p>
  
  <hr>
  
  <p>I am looking for built in surport for "<a href="http://en.wikipedia.org/wiki/Push_technology" rel="nofollow noreferrer">long polling</a>" / "<a href="http://en.wikipedia.org/wiki/Comet_(programming)" rel="nofollow noreferrer">Comet</a>" etc</p>
  
  <hr>
  
  <p>Thanks for the most informative answer from Drew Marsh on how to implement long polling in WCF.  However I thought the main “selling point” of WCF was that you could do this sort of thing just by configuring the channels to be used in the config file.  <em>E.g I want a channel that logically two way but physically incoming only.</em></p>