At 12:40 20/10/2005, 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.

This is a good example of the not-so-obvious limitations of 128Kbit upstream.

Assuming that the 128Kbit limit is here to stay for the forseeable
future the only choice is to do QoS on on the upstream traffic and
give prioritization to acks, and for good measure do something like
sfq as well to avoid any one stream from hogging the available bandwidth.

As a workaround you could insert a device that can do QoS and traffic
shapping between the ADSL router and the lan, and there are some that
can even do this in bridging mode such as the Cyberguard's which
makes it transperant to the existing network setup.

Regards,
Simon

-- 
This message is part of the NZ ADSL mailing list. 
see http://unixathome.org/adsl/ for archives, FAQ, 
and various documents. 
To unsubscribe: send mail to majordomo@lists.unixathome.org 
with "unsubscribe adsl" in the body of the message