kernel optimization for long distance download??

[Baruch Even]

2010/3/6 Shachar Shemesh <shachar at shemesh.biz>

>  Ohad Levy wrote:
>
> You would need to know what to sniff, e.g. if tcp dynamic window scaling is
> enabled.
>
>  I'll be interested in what you consider dirty tricks?
> AFAIK increasing the tcp window size (read: send more data for every ack)
> is not considered dirty trick at all, and is very efficient with good
> connections (low packet drop) and high latency.
>
>  Ohad
>
> The legal tricks are, mainly, two.
>

There are several things to note here, you should use a congestion control
algorithm that is better optimized for the long-fast-pipe case, the default
of the linux kernel is bic which is better than the reno/newreno case. But
you can also try cubic and htcp. Be sure to increase the default and maximum
send/receive windows to allow the window scale to be set high enough to make
use of the bandwidth. You should also ensure that you are running a
sufficiently new kernel as very old kernels (circa 2.6.16) had various bugs
in bic and/or sack processing that prevented them really hitting it to the
max.

Another approach is to use vegas/westwood and such congestion control that
do not work based on packet loss but rather go for delay, but they are
problematic in the normal Internet since there are losses and they interact
badly with such algorithms severely limiting their usefulness.

Baruch
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