var timerHit = 2 * 1000 * 60 ; // executes interval functions at each 2 minute(s)
var timerAliveObj = null;
function forceKeepAlive() 
{
    var imgAlive = document.getElementById("keepAliveImg");
    if(!imgAlive)
        return;
    var rndParam = Math.round(100*Math.random());
    imgAlive.src = String( imgAlive.src ).replace(/\?.*$/, '?xrand=' + rndParam);           
}
timerAliveObj = window.setInterval("forceKeepAlive()", timerHit);