var keepAlive = '../KeepAlive.aspx';
var ping_delay_seconds = 60;
var reqPing = createXMLHttpRequest();

function sendPing() {
        var str = "";       
        reqPing.open("GET", keepAlive);      
        reqPing.onreadystatechange = handlePingResponse;
        reqPing.send(null);
        return false;
    }

  
  function handlePingResponse() {
        if(reqPing.readyState == 4){
            var response = reqPing.responseText;
            //alert('Ping: '+response);
        }
    }

   function createXMLHttpRequest() {
        var xmlHttp;
        try {
          // Firefox, Opera 8.0+, Safari
          xmlHttp=new XMLHttpRequest();
        }
        catch (e) {
          // Internet Explorer
          try {
            xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
          }
          catch (e) {
            try {
              xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
            }
            catch (e){
              alert("Your browser does not support AJAX!");
              return false;
            }
          }
        }
        return xmlHttp;
    }

setInterval("sendPing()", ping_delay_seconds*1000);