On 10/30/2012 02:24 PM, Felix Fietkau wrote:
On 2012-10-30 2:00 PM, Mathias Kretschmer wrote:
On 10/30/2012 01:43 PM, Felix Fietkau wrote:
On 2012-10-30 1:07 PM, Simon Wunderlich wrote:
From: Mathias Kretschmer <mathias.kretschmer@xxxxxxxxxxxxxxxxxxx>
According to 802.11-2007 17.3.8.6 (slot time), the slot time should
be increased by 3 us * coverage class. The code only increased the
ack timeout, which is fixed by this patch.
We have noticed in our long shot scenario that we see less collisions
with this patch.
At some point I had the slot time increase in the driver, but noticed a
massive throughput degradation on 10-20 km links. Leaving the slot time
alone and changing only the ACK timeout fixed this. What distances did
you test?
about 11km. did you test UDP (unidirectional) or TCP (bidirectional) throughput ?
I always use TCP, because UDP tests are too unrealistic to estimate real
performance.
bidirectional UDP traffic (iperf or preferably mgen) is a good indicator for
problems, because there's no flow control that backs off. depends on the use case,
of course.
The larger slot time will increase the channel access overhead which should impact
unidirectional throughput.
With bidirectional traffic, the larger slottime should help to minimize collisions
on loaded links. Overall this seems to increase the net throughput for us,
especially in higher access categories (smaller backoff windows).
When I ran the test, the throughput degradation was so big that the
links became almost useless. It was a long time ago, so maybe this was
caused by another bug that has been fixed since. I will run another test
with this patch in a current version...
we will also test this again. Currently, I can't access those links.
Cheers,
Mathias
- Felix
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