var iid;
function keepAlive(sessid){
    var http=createRequestObject();
    http.open("get","keepalive.php?sessid="+sessid,true);
    http.onreadystatechange=function(){
        if(http.readyState==4){
            if(!iid){
                iid=setInterval("keepAlive('"+sessid+"')",1000*60*7);
            }
        }
    }
    http.send(null);
}