Date: Thu, 21 Jul 2005 07:36:06 +0100 From: David Malone <dwmalone@maths.tcd.ie> To: Sam Pierson <samuel.pierson@gmail.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: Atheros, hardware access layer, collisions Message-ID: <20050721063606.GA33233@walton.maths.tcd.ie> In-Reply-To: <d9204e4c0507202003231add5a@mail.gmail.com> References: <d9204e4c0507202003231add5a@mail.gmail.com>
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On Wed, Jul 20, 2005 at 10:03:49PM -0500, Sam Pierson wrote: > I think there is still collision detection happening on the hardware > level. I think I have to disable the retransmission of frames > which are lost due to collisions. Here's my reasoning: In the lab, two > hosts are sending packets to the middle guy at the same time. > After examining the traffic on the middle guy, one packet will > arrive before the other one (sometimes in different order) and > the second packet comes 500-1200us after the first. From this, > I think some retransmission is happening because of collision, > since the results are seemingly random. Since introducing random delays before transmission and using carrier sensing are basic features of the 802.11 MAC, I'd be suprised if you can stop the hardware doing it. To reduce the effects as much as possible, you could try trying to reduce the number of retransmission attempts and changing the cwmin parameter to be small. Even if you do this, you'll still need to transmit the packets quite close to one another (probably within 20us) to avoid the carrier sense stuff kicking in. What effect are you trying to achieve? David.
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