Hi,

Lately I encounter quite interesting problem on my network.
I have 512/512 kbit/s link from my isp and everything seems to be fine
when I'm uploading I have something about 512kb/s when I'm testing
download I have about 512kbit/s :). This works fine both on Windows XP
and Gentoo. Problem starts when I'm testing up/down simultaneously then I
have down ~500 and up ~ 200 kbit/s on widnows and ~500/500 on gentoo.
I wonder where is the difference between Windows and Linux and if there
is any chance to solve this problem.

Thanks in Advance

Pozdrawiam
Mroofka

On Mon, 18 Aug 2008 12:28:16 +0000 (UTC), Szymon Turkiewicz wrote:
> Hi,
>
> Lately I encounter quite interesting problem on my network.
> I have 512/512 kbit/s link from my isp and everything seems to be fine
> when I'm uploading I have something about 512kb/s when I'm testing
> download I have about 512kbit/s :). This works fine both on Windows XP
> and Gentoo. Problem starts when I'm testing up/down simultaneously then I
> have down ~500 and up ~ 200 kbit/s on widnows and ~500/500 on gentoo.
> I wonder where is the difference between Windows and Linux and if there
> is any chance to solve this problem.

Sounds like a driver issue. I'd look for a driver update for Windows.

--
* John Oliver http://www.john-oliver.net/ *

Dnia Mon, 18 Aug 2008 17:30:30 +0200, John Oliver napisał(a):

> On Mon, 18 Aug 2008 12:28:16 +0000 (UTC), Szymon Turkiewicz wrote:
>> Hi,
>>
>> Lately I encounter quite interesting problem on my network. I have
>> 512/512 kbit/s link from my isp and everything seems to be fine when
>> I'm uploading I have something about 512kb/s when I'm testing download
>> I have about 512kbit/s :). This works fine both on Windows XP and
>> Gentoo. Problem starts when I'm testing up/down simultaneously then I
>> have down ~500 and up ~ 200 kbit/s on widnows and ~500/500 on gentoo. I
>> wonder where is the difference between Windows and Linux and if there
>> is any chance to solve this problem.
>
> Sounds like a driver issue. I'd look for a driver update for Windows.

I'm almost sure this is not the problem. I've made tests on few different
notebooks and on WindowsXP and Windows2000.

Pozdrawiam
Szymon Turkiewicz

Szymon Turkiewicz wrote:
> Dnia Mon, 18 Aug 2008 17:30:30 +0200, John Oliver napisał(a):
>
>> On Mon, 18 Aug 2008 12:28:16 +0000 (UTC), Szymon Turkiewicz wrote:
>>> Hi,
>>>
>>> Lately I encounter quite interesting problem on my network. I have
>>> 512/512 kbit/s link from my isp and everything seems to be fine when
>>> I'm uploading I have something about 512kb/s when I'm testing download
>>> I have about 512kbit/s :). This works fine both on Windows XP and
>>> Gentoo. Problem starts when I'm testing up/down simultaneously then I
>>> have down ~500 and up ~ 200 kbit/s on widnows and ~500/500 on gentoo. I
>>> wonder where is the difference between Windows and Linux and if there
>>> is any chance to solve this problem.
>> Sounds like a driver issue. I'd look for a driver update for Windows.
>
> I'm almost sure this is not the problem. I've made tests on few different
> notebooks and on WindowsXP and Windows2000.
>

How are you testing the speed? If you are using tcp connections, then
for every transferred packet there is an acknowledge packet going in the
opposite direction. There is also normally other traffic in both
directions - things like DNS lookups and transfer handshakes. If
windows is badly prioritising the packets so that all the bandwidth in
one direction is completely filled with data packets, the other
direction could quickly be stalled because the small but critical
handshaking packets are delayed. You can read about this sort of thing
on webpages about bittorrent clients - they normally recommend that you
limit download and upload bandwidth to slightly lower than your full
rate to avoid this sort of stalling.

Szymon Turkiewicz wrote:
> Hi,
>
> Lately I encounter quite interesting problem on my network.
> I have 512/512 kbit/s link from my isp and everything seems to be fine
> when I'm uploading I have something about 512kb/s when I'm testing
> download I have about 512kbit/s :). This works fine both on Windows XP
> and Gentoo. Problem starts when I'm testing up/down simultaneously then I
> have down ~500 and up ~ 200 kbit/s on widnows and ~500/500 on gentoo.
> I wonder where is the difference between Windows and Linux and if there
> is any chance to solve this problem.

As David already said it's generally bad for tcp when you have bulk
traffic in both directions as the acks get delayed in the queue.

The main difference between Linux and XP/2K TCP is that by default Linux
uses window scaling and XP/2K don't. This means that XP/2K won't ever
have more than 64k unacked data in transit. There are no doubt other
differences as well and what exactly is happening for you will depend on
things like buffer sizes in modem/at ISP, how far away the other end of
the connection is and what settings that server uses.

Andy.

>> Hi,
>>
>> Lately I encounter quite interesting problem on my network. I have
>> 512/512 kbit/s link from my isp and everything seems to be fine when
>> I'm uploading I have something about 512kb/s when I'm testing download
>> I have about 512kbit/s :). This works fine both on Windows XP and
>> Gentoo. Problem starts when I'm testing up/down simultaneously then I
>> have down ~500 and up ~ 200 kbit/s on widnows and ~500/500 on gentoo. I
>> wonder where is the difference between Windows and Linux and if there
>> is any chance to solve this problem.
>
> As David already said it's generally bad for tcp when you have bulk
> traffic in both directions as the acks get delayed in the queue.
>
> The main difference between Linux and XP/2K TCP is that by default Linux
> uses window scaling and XP/2K don't. This means that XP/2K won't ever
> have more than 64k unacked data in transit. There are no doubt other
> differences as well and what exactly is happening for you will depend on
> things like buffer sizes in modem/at ISP, how far away the other end of
> the connection is and what settings that server uses.

Hi,


I've found problem. I've upgraded kernel from 2.6.19 to 2.6.23 on router
and there was a change in IMQ.

2.6.19
4: imq0: <NOARP,UP,10000> mtu 1500 qdisc hfsc qlen 30
2.6.23
4: imq0: <NOARP,UP,10000> mtu 16000 qdisc hfsc qlen 11000

after setting mtu and qlen like in 2.6.19 kernel problem disappeared. now
I have 60/60kB in tests.

Thanks for your time and advices.

Now I would like to learn which exactly is qlen and how it could be used
to tune my routers but this is another topic :)

Pozdrawiam
Mroofka