From owner-freebsd-mobile@FreeBSD.ORG Tue Oct 4 23:43:30 2005 Return-Path: X-Original-To: freebsd-mobile@freebsd.org Delivered-To: freebsd-mobile@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 5D9BD16A41F for ; Tue, 4 Oct 2005 23:43:30 +0000 (GMT) (envelope-from samuel.pierson@gmail.com) Received: from wproxy.gmail.com (wproxy.gmail.com [64.233.184.201]) by mx1.FreeBSD.org (Postfix) with ESMTP id E3A2343D45 for ; Tue, 4 Oct 2005 23:43:29 +0000 (GMT) (envelope-from samuel.pierson@gmail.com) Received: by wproxy.gmail.com with SMTP id 71so15870wra for ; Tue, 04 Oct 2005 16:43:29 -0700 (PDT) DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:reply-to:to:subject:mime-version:content-type:content-transfer-encoding:content-disposition; b=YrQjnNk+3kyEWjzIzAukGLDDiW66+NjJBCrKJ0f9YluegBohtl1oVgNoBtaHk1fQjU6JGK0biqLq8KWcwSfaDeMjrk/8lxvO5VfNKRG5VxtG8DEEIuk8xB5fLlhcM9rxbwkHldles97Ragkdzch2Gww0sfAo4TUYyMMGDDZ+paE= Received: by 10.54.114.10 with SMTP id m10mr64756wrc; Tue, 04 Oct 2005 16:43:29 -0700 (PDT) Received: by 10.54.144.19 with HTTP; Tue, 4 Oct 2005 16:43:29 -0700 (PDT) Message-ID: Date: Tue, 4 Oct 2005 18:43:29 -0500 From: Sam Pierson To: freebsd-mobile@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Subject: Different ACK response times in ath? X-BeenThere: freebsd-mobile@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Sam Pierson List-Id: Mobile computing with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 04 Oct 2005 23:43:30 -0000 Hi all, Recently I had to do some measurements and came up with some interesting results with the ath driver. I would take two machines associated to an AP and ping the second with the first. This produces four data frames: A --> AP : echo request AP --> B: echo request B --> AP: echo response AP -> A: echo response Each of these directed data frames results in an ACK packet being generated by the destination. I monitor all traffic using a passive third laptop, which also records elapsed time between frames (specifically between data frames and ACK packets). Under channel 11, which has a lot of traffic, I had these results: (times refer to elapsed time between data and ACK frames) Using an IBM TP T42: D-link DWL-G630: ~248us Netgear WG511T ~210us Using IBM TP X23: D-link: ~208us WG511T: ~210us internal prism 2.5: ~256us Apple Airport: ~250us Why would these values be different? Additionally, on channel 6 (with little traffic), when using one of the machines in hostAP mode: X24: netgear: 114us dlink: 109us airport: ~154us Shouldn't ACK packets be transmitted a constant delay after directed data frames have been received? Isn't this the way the 802.11 standard is defined? Why is the slower computer responding faster than the faster computers when the TPs are running the same drivers (and versions)? -- Sam