Re: [Madwifi-devel] Adhoc mode packet loss

[Derek S. <de...@in...>]

Hi,

I think that to ensure the diversity does exactly the right thing, I 
sugguest that you hard code it.

  alter the if_ath.c file.
  After every call to ath_hal_reset(), put in a call to set the txdiveristy 
and rx diversity.
Further, go through and remove all places that switch antenna, so that the 
code is definately only using 1 antenna.

This improves the chance that something strange with diversity is not 
going on.

Interesting - you note that working on diversity has reduced the loss rate 
from 50% to 30%

=================
setup a second node with a radio in monitor mode and collect 
packets with tcpdump/wireshark. Look at the packets on air.
See what the receive power levels are, and look at the variation between 
packets.

=================
Slottime distance settings. If your links are long (> 300 meters), you 
will need to set the slottime to be longer
   ath_ctrl -d 5000

=================
Is there a combination you can use that reduces the loss rate - nodes 
closer together perhaps, different tx output power, different connections 
etc. In a previous letter you noted that with infrastructure mode you get 
no loss. This says it is not a connector/antenna/wrong_tx_power/distance 
problem.

=================
rts/cts - In some installations, it works best if these are off.

=====================================
rate control module.

Use Minstrel. Minstrel works. Minstrel is reliable, and works for days 
and days and days and days and days.

Felix Fietkau wrote in a letter to me on the topic of Minstrel:

>- I haven't heard a single case of minstrel being outperformed on 
>mac80211 by something else yet.
>
>- It seems like whenever somebody complains about low throughput with a 
>mac80211 the default answer has become 'try minstrel' ;)


===========================================================================
On Wed, 4 Feb 2009, Candy Yiu wrote:

> Thanks for the reply.
> I tried to disable the antenna diversity and set only antenna 1 for tx and
> rx.

> However, it seems to have 3 pkts loss for every 10 pkts. I am trying to 
> use 802.11a at freq 5.745G so that there is less traffic -> less 
> collision. I am not sure if the problem solve or not. Any clue?
>
> thanks again,
> Candace
>
> On Wed, Feb 4, 2009 at 1:52 AM, Derek Smithies <de...@in...> wrote:
>
>> Hi,
>>
>> My guess:
>>  Diversity is on.
>>  It is attempting to use both antenna connections, but you have just one
>> antenna connected.
>>
>> My experience in adhoc is that you should get packet loss below 1% for
>> hundred meter long links.
>>
>> Derek.
>>
>>
>> On Tue, 3 Feb 2009, Candy Yiu wrote:
>>
>>  Hi there,
>>>
>>> I am experiencing lots of packet loss in adhoc mode using madwifi.
>>> I am sending 100000 pkts using UDP between two nodes. It works
>>> just fine when it is using infrastructure mode. When I use adhoc mode,
>>> almost every other pkt is loss (50% in total).
>>>
>>> Any idea and help would be appreciate. thanks!
>>>
>>> --
>>> Candace YIU
>>> student, Computer Science
>>> Portland State University
>>> http://web.pdx.edu/~candy <http://web.pdx.edu/%7Ecandy>
>>>
>>>
>>>
>> --
>> Derek Smithies Ph.D.
>> IndraNet Technologies Ltd.
>> Email: de...@in...
>> ph +64 3 365 6485
>> Web: http://www.indranet-technologies.com/
>>
>>
>
>
> --
> Candy YIU
> student, Computer Science
> Portland State University
> http://web.pdx.edu/~candy
>

-- 
Derek Smithies Ph.D.
IndraNet Technologies Ltd.
Email: de...@in...
ph +64 3 365 6485
Web: http://www.indranet-technologies.com/