Timing problems.

Pablo Berra hostap at laufquen.com.ar
Tue Nov 19 09:20:31 EST 2002


Re: Timing problems.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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