var objXHttp;

function aggiorna_sessione()
{
  var url = "ajax_sessione.php?r=" + Math.random()*12345;
  objXHttp = GetBrowser(SChange);
  objXHttp.open("GET", url, true);
  objXHttp.send(null);
}

function SChange()
{
 if (objXHttp.readyState == 4)
 {
  //var OP = document.getElementById();
  //OP.innerHTML = objXHttp.responseText;
 }
}

function GetBrowser(BrowserName)
{
 if (navigator.userAgent.indexOf("MSIE") != (-1))
 {
  var XmlClassName = "Msxml2.XMLHTTP";
  if (navigator.appVersion.indexOf("MSIE 5.5") != (-1));
  {
   XmlClassName = "Microsoft.XMLHTTP";
  } 
  try
  {
   OggettoobjXHttp = new ActiveXObject(XmlClassName);
   OggettoobjXHttp.onreadystatechange = BrowserName;
   return OggettoobjXHttp;
  }
  catch(e)
  {
   alert("Errore: l'ActiveX non verrą eseguito!");
  }
 }
 else if (navigator.userAgent.indexOf("Mozilla") != (-1))
 {
  OggettoobjXHttp = new XMLHttpRequest();
  OggettoobjXHttp.onload = BrowserName;
  OggettoobjXHttp.onerror = BrowserName;
  return OggettoobjXHttp;
 }
 else
 {
  OggettoobjXHttp = new XMLHttpRequest();
  OggettoobjXHttp.onload = BrowserName;
  OggettoobjXHttp.onerror = BrowserName;
  return OggettoobjXHttp;
 }
}

function timeout_sessione() {

aggiorna_sessione();

window.setTimeout("timeout_sessione()", 60000);

}
timeout_sessione();