Timing problems.

Pablo Berra hostap at laufquen.com.ar
Tue Nov 19 11:34:49 EST 2002


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I try this, but didn't work.
I suppose that the problems is that the sender doesn't receive the ACK in
time, and thinks that the packet is lost.
All RF are ok (good link quality, stable 11Mbit rate, >20 dB of system
operating marging), the ping response are excelent (I can send 1000 packets,
without loose anyone, with a delay time between 4 and 12 ms), but if I load
the link the things come very bad.
For example, with netperf the bandwidht is about 0.08 Mbits, getting a
little better with retransmissions set to 0, but below to 0.3 Mbits.
By the way, I have several <25 km links, and they works great with similar
configurations (speeds over 3.5 Mbit), I have this problem only with a 36km
and a 41km link.

This article explains the problem:
http://www.personaltelco.net/index.cgi/MaximumDistance

I found that StarOS solve this problem with the Agere cards, and Cisco has a
distance factor on they bridges to adjust the 802.11b timing.
I don't know if the ACK times are firmware or driver controlled, and if they
can be modified on Prism.

Does anybody have an idea?
Does anybody know a working >35km link with Prism and HostAP?
If the answer to the last one is no, does anybody know a working >35km link
and what hard/soft it use?

Thanks in advance!
Pablo.

----- Original Message -----
From: Jouni Malinen
To: hostap at shmoo.com
Sent: Tuesday, November 19, 2002 2:13
Subject: Re: Timing problems.


On Mon, Nov 18, 2002 at 10:30:02PM +0200, Vladimir Ivaschenko wrote:

> BTW, are there any 802.11b cards available which allow to change CIFS/DIFS
> intervals or to disable retransmissions with open source drivers?

I'm not aware of how these intervals could be changed in Prism2 cards,
but you should be able to setup retransmission limit with Host AP
driver. If you set the maximum number of retransmission to 0, there
should not be any retransmissions even if the frames are not
acknowledged. I haven't tested this thoroughly, but you can test it by
running 'iwconfig wlan0 retry 0'.

--
Jouni Malinen                                            PGP id EFC895FA
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