function ping( url, cb )
{
    if ( url.indexOf( "?" ) >= 0 )
    {
        url += "&rnd=" + Math.random();
    }
    else
    {
        url += "?rnd=" + Math.random();
    }
    
    var req = getXmlRequest();
    if ( req )
    {
        if ( cb )
        {
            req.onreadystatechange = function() { 
                if ( req.readyState == 4 ) { cb( req.responseText ); }
            };
        }
        
        req.open( "GET", url, true );
        req.send();
    }
}

function getXmlRequest()
{
    var r = null;
    if ( window.ActiveXObject )
    {
        r = new ActiveXObject( "Msxml2.XMLHTTP" );
        if ( r == null )
        {
            r = new ActiveXObject("Microsoft.XMLHTTP");
        }
     }
     else if ( window.XMLHttpRequest ) 
     {
        r = new XMLHttpRequest;
     }
     
     return r;
}