protected abstract void makeKey( Request request ) throws IOException;
    protected abstract Request peekKey() throws IOException;
    protected abstract void doSend( Request request ) throws IOException;
    protected abstract void doRecv( Response response ) throws IOException;
    protected abstract void doSkip() throws IOException;

    public synchronized void sendrecv( Request request,
                    Response response,

    /**
     * @param request
     * @param response
     * @param params
     * @param timeout
     * @param firstKey
     * @return
     * @throws IOException
     */
    private <T extends Response> long prepareRequests ( Request request, T response, Set<RequestParam> params, long timeout ) throws IOException {
        Response curResp = response;
        Request curReq = request;
        long firstKey = 0;