Thinking about it further; its probably best to prioritise packets by
size (give small packets higher priority).

That way small but important packets like DNS queries and TCP
handshaking would not be obstructed by large upstream traffic like SMTP.

-----Original Message-----
From: Russell Fulton [mailto:r.fulton@auckland.ac.nz]
Sent: Thursday, 20 October 2005 1:03 p.m.
To: Philip D'Ath
Cc: ADSL List
Subject: Re: 128Kb/s Upstream Throttles 2Mb/s downstream

you can mitigate some of this by prioritising ACKs on the up link.
There has been quite a bit of discussion about doing this with OBSD's pf
firewall on the pf mailing list.

Russell

Philip D'Ath wrote:
> Ran into an interesting problem the other day.
>
> Had a business customer that was on full speed JetStream. They were
> forced to move to UBS like everyone else, but liked the speed, so
> decided to go for a 2Mb/s plan.
>
> They gave me a call the other day complaining their WWW browsing was
> very poor. Assumed it was related to the ISP, but decided to
> investigate further.
>
>
> 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.
>

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