title: Throttle number of requests across WCF services
body: <p>I have a WCF service load balanced across three different machines.  </p>
  
  <p>Let's say these services can process requests of types <strong>A</strong>, <strong>B</strong>, and <strong>C</strong>.   There are no limits to processing <strong>A</strong> or <strong>B</strong>.  However, we can only process 5 requests of type <strong>C</strong> at a time, so if a 6th request of type <strong>C</strong> comes in, it'll have to wait until one of the previous requests finish.  </p>
  
  <p>How can I make sure that only 5 requests of type <strong>C</strong> are being processed across all three machines?</p>