How to correctly limit bandwith usage with Java netty?

For a download client that I developed in Java using the netty nio lib I also implemented a bandwith limitation feature. Technically I do so via a GlobalTrafficShapingHandler object. Based on this class' JavaDoc I initialize the nio client pipeline as follows:

...
trafficHandler = new GlobalTrafficShapingHandler(
        new HashedWheelTimer(), 0, 0, 1000);
execHandler = new ExecutionHandler(
        new OrderedMemoryAwareThreadPoolExecutor(20, 0, 0));
...

public ChannelPipeline getPipeline() throws Exception
{
    // create default pipeline
    ChannelPipeline pipeline = pipeline(); 

    // traffic shaping handler
    pipeline.addLast("global-traffic-shaping", trafficHandler);

    // SSL support
    if(useSSL)
    {
        SSLEngine sslEngine = createSSLEngine();
        pipeline.addLast("ssl", new SslHandler(sslEngine));
    }

    // memory executor
    pipeline.addLast("memory-executor", execHandler);

    // business logic
    pipeline.addLast("data-processing", 
        new NettyNioClientHandler(
            nettyNioClient, localer, logger, ncMgr, username, useSSL));

    return pipeline;
}

And during runtime I then set the max. download speed via

public void setDlSpeedLimit(long limit)
{
    if(limit < 0)
        return;

    trafficHandler.configure(0, limit * 1000L);
}

Ok, so basically the netty nio functionality works fine and fast. When I set the max. download speed in the application, I can also see that the bandwidth usage is indeed capped at a max. level. I monitor the bandwith usage via

trafficHandler.getTrafficCounter().getLastReadThroughput();

However, unfortunately the max. speed I monitor is not to what I have set it before, not even close. For example, I originally (w/o limit) have a download speed of about 2000 kb/s, then I set the limit to 300 kb/s as described above, but the real download speed is then varying from 700-900 kb/s.

So my problem in this case is: I can see that the traffic shaper is doing something, but not as I wanted it to. Do I miss something here, any step in the pipeline initialization for example?

Thanks in advance for your help!

Ok, so it seems there are not other ideas.
The only thing that helped me a bit was to increase the timing counter to 5-10 sec.

Cheers!