private void processGetReplica(Sim_event ev)
    {
        if (ev == null) {
            return;
        }

        Object[] data = (Object[]) ev.get_data();
        if (data == null) {
            return;
        }

        String filename = (String) data[0];         // get file name
        Integer sender = (Integer) data[1];         // get sender id

        // creates an object that contains the required information
        Object[] dataTemp = new Object[3];
        dataTemp[0] = filename;

        ArrayList list = (ArrayList) catalogueHash_.get(filename);
        if (list != null) {
            dataTemp[1] = (Integer) list.get(0);
        } else {
            dataTemp[1] = new Integer(-1);
        }

        // sends back the result to sender
        super.send(super.output, 0, DataGridTags.CTLG_REPLICA_DELIVERY,
            new IO_data(dataTemp, DataGridTags.PKT_SIZE, sender.intValue()) );
    }