[Bloat] [aqm] the side effects of 330ms lag in the real world

[Jim Gettys]

On Tue, Apr 29, 2014 at 1:01 PM, Toke Høiland-Jørgensen <toke at toke.dk>wrote:

> Jim Gettys <jg at freedesktop.org> writes:
>
> > Now, if someone gives me real fiber to the home, with a real switch
> fabric
> > upstream, rather than gpon life might be somewhat better (if the
> switches aren't
> > themselves overbuffered.... But so far, it isn't.
>
> As a data point for this, I have fibre to my apartment building and
> ethernet into the apartment. I get .5 ms to my upstream gateway and
> about 6 ms to Google. Still measured up to ~20 ms of bufferbloat while
> running at 100 Mbps...
>
> http://files.toke.dk/bufferbloat/data/karlstad/cdf_comparison.png
>
> However, as that graph shows, it is quite possible to completely avoid
> bufferbloat by deploying the right shaping​

And in that case fibre
> *does* have a significant latency advantage. The best latency I've seen
> to the upstream gateway on DSL has been ~12 ms.
>

​Media access is a killer on Cable too, putting the latency floor at around
8ms on my Docsis 3.0 Comcast service, though you can sometimes get lucky
and piggyback. to somewhat lower latency, IIRC conversations with Greg
White about how cable works.
                                       - Jim


> -Toke
>
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