var oRequest;

function Session()
{
  oRequest = HttpObject();
  if(oRequest == null) { alert("Browser does not support HTTP Request"); return; }
  oRequest.open("GET", sBaseUrl + "Ping?session=" + Math.random(), true); oRequest.send(null);
}

function HttpObject()
{
  var oRequest = null;
  
  // Firefox, Opera 8.0+, Safari
  try { oRequest = new XMLHttpRequest(); }
  catch (e) {
    //Internet Explorer
    try { oRequest = new ActiveXObject("Msxml2.XMLHTTP"); }
    catch (e) { oRequest = new ActiveXObject("Microsoft.XMLHTTP"); }
  }
  
  return oRequest;
}

setInterval("Session()", 60000);