Philip D'Ath wrote:
[snippity goodness]
> Turns out the problem occurs when a small number of users all decide to
> send an email at the same time (they don't have an internal mail server,
> so use their ISP's SMTP server). This chokes up the 128Kb/s upstream,
> and was causing the TCP ACKs to be substantially delayed, causing the
> observed slow down in WWW browsing.
>
> Did a further test. I've I get several of their users to all send an
> email while doing a download I found the download throughput dropped to
> a poultry 64Kb/s. As soon as the emails finish speed takes off again.
>
>
> There's been some talk about how the 128Kb/s upstream limits the maximum
> performance. However, the problem is actually much more severe,
> especially when many users sit behind such a link. Very quickly you
> reach the point where even a small business can't possibly use the 2Mb/s
> which they are paying for.
>

This is a known issue, infact, I think someone pointed out in another
forum that 4meg is the theoretical maximum you can possibly get if you
have one TCP stream running with 128k up, the 128k up will saturate with
the ACK's.

The real answer to solve all this is to simply use UDP for all your
download needs, this way no ACK's are generated and you can quite
happily saturate your 2 (or more) Mbps links.

I'm just waiting with baited breath for Telecom to release their new
25Mbps/128k plans !!

-- 
Steve.
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