private void handleModifyReservation(Sim_event ev)
    {
        int src = -1;   // the sender id
        boolean success = false;
        int tag = -1;

        try
        {
            // get the data
            ARObject obj = (ARObject) ev.get_data();

            // get the unique tag to send back to recepient
            int returnTag = GridSimTags.RETURN_AR_MODIFY;
            tag = returnTag + obj.getTransactionID();

            src = obj.getUserID();  // get the sender ID

            // check whether this resource can support AR or not
            success = checkResourceType(src, returnTag, obj.getTransactionID(),
                            GridSimTags.AR_MODIFY_FAIL_RESOURCE_CANT_SUPPORT,
                            "can't modify an existing reservation");

            // if this resource doesn't support AR then exit
            if (!success) {
                return;
            }
            else {
                ((ARPolicy) policy_).handleModifyReservation(obj, src, tag);
            }
        }
        catch (ClassCastException c) {
            success = false;
        }
        catch (Exception e) {
            success = false;
        }

        // if there is an exception, then send back an error msg
        if (!success && tag != -1)
        {
            System.out.println(super.get_name() + " : Error - can't modify an "+
                " existing reservation.");

            super.send(src, 0.0, GridSimTags.RETURN_AR_MODIFY,
                new IO_data(new Integer(GridSimTags.AR_MODIFY_ERROR),SIZE,src));
        }
    }