static function instance( $transport = false, $forceNewInstance = false )
    {
        $ini = eZINI::instance( 'notification.ini' );
        if ( $transport == false )
        {
            $transport = $ini->variable( 'TransportSettings', 'DefaultTransport' );
        }
        $transportImpl =& $GLOBALS['eZNotificationTransportGlobalInstance_' . $transport ];
        $class = $transportImpl !== null ? strtolower( get_class( $transportImpl ) ) : '';

        $fetchInstance = false;
        if ( !preg_match( '/.*?transport/', $class ) )
                $fetchInstance = true;

        if ( $forceNewInstance  )
        {
            $fetchInstance = true;
        }

        if ( $fetchInstance )
        {
            $extraPluginPathArray = $ini->variable( 'TransportSettings', 'TransportPluginPath' );
            $pluginPathArray = array_merge( array( 'kernel/classes/notification/' ),
                                            $extraPluginPathArray );
            foreach( $pluginPathArray as $pluginPath )
            {
                $transportFile = $pluginPath . $transport . 'notificationtransport.php';
                if ( file_exists( $transportFile ) )
                {
                    include_once( $transportFile );
                    $className = $transport . 'notificationtransport';
                    $impl = new $className( );
                    break;
                }
            }
        }
        if ( !isset( $impl ) )
        {
            $impl = new eZNotificationTransport();
            eZDebug::writeError( 'Transport implementation not supported: ' . $transport, __METHOD__ );
        }
        return $impl;
    }