From owner-freebsd-mobile@FreeBSD.ORG Fri Mar 17 20:51:29 2006 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 A923216A41F for ; Fri, 17 Mar 2006 20:51:29 +0000 (UTC) (envelope-from kan.cai@gmail.com) Received: from zproxy.gmail.com (zproxy.gmail.com [64.233.162.195]) by mx1.FreeBSD.org (Postfix) with ESMTP id CF3CA43D48 for ; Fri, 17 Mar 2006 20:51:28 +0000 (GMT) (envelope-from kan.cai@gmail.com) Received: by zproxy.gmail.com with SMTP id 9so673057nzo for ; Fri, 17 Mar 2006 12:51:28 -0800 (PST) DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:mime-version:content-type; b=BanHG6fDwR6Y9Cccciu60GK++v90PrxhUJDrEewmeA5fRvSWN6/xygxCrjTzDvIJ2CuM27sYLruTCIvQzmvBLHtZZmeoG/vbFlcck8zF42gkNRF056ceUwBrOgd3HIq88oVDEoYOh6tesnSbtJl4AZ6C5TQP6/rXeVDTICrhbAQ= Received: by 10.37.14.56 with SMTP id r56mr4456033nzi; Fri, 17 Mar 2006 12:51:28 -0800 (PST) Received: by 10.36.38.14 with HTTP; Fri, 17 Mar 2006 12:51:27 -0800 (PST) Message-ID: <5365ea660603171251w330dcfbds316e73c83038aa3c@mail.gmail.com> Date: Fri, 17 Mar 2006 12:51:27 -0800 From: "Kan Cai" To: freebsd-net@freebsd.org, freebsd-mobile@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: Subject: Wireless sensing function is missing? X-BeenThere: freebsd-mobile@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Mobile computing with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 17 Mar 2006 20:51:29 -0000 Greetings all: I have been doing some 802.11 wireless experiments, and the reults seem t= o suggest that wireless sensing function is missing. In theory, a wireless device should back off when it senses some signals in the airspace, even if these signals are too weak to capture, just to avoid potential packet drops due to collisions. The experiment I did is to measure the UDP sending and recving rates by putting two wireless nodes on the verge of transmission range, and then putting rectangle garbage bins stuffed with books in front of one wireless node to absorb the signal. Here are the results: # of garbage bins Sending Rate Recving Rate 1 4.77Mbps 3.32Mbps 2 5.83Mbps 2.26Mbps 3 7.73Mbps 0.48Mbps 4 8.18Mbps 0.00Mbps The other wireless node is sending UDP packet at maximum rate 8.2Mbps. Even though the impact of interference weakens as I put more garbage cans= , the sum of the sending rate and receving rate as shown is about 8.1-8.2Mbps= , which suggests that it is not affect by those sensing signals. Otherwise, i= t would back off its transmissions until the network is idle. It can still receive some packets sent by another node, which indicates that it should b= e able to sense most of the signals although it might not be able to receive them. I wonder if this is true that sensing function is missing? If yes, is it supposed to be implemented in the driver or net80211 layer? Thanks in advance! cheers, --ken