window.onload = function() {
  setInterval(ping, 300000);
}

function ping()
{
   if (window.ActiveXObject)
   {
      httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
   }
   else
   {
      httpRequest = new XMLHttpRequest();
   }
   httpRequest.open("GET", "ping.txt", true);
   httpRequest.send(null);
}