Return-path: Received: from smtp-out.google.com ([216.239.44.51]:53293 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753993Ab0IUAaO convert rfc822-to-8bit (ORCPT ); Mon, 20 Sep 2010 20:30:14 -0400 Received: from kpbe15.cbf.corp.google.com (kpbe15.cbf.corp.google.com [172.25.105.79]) by smtp-out.google.com with ESMTP id o8L0UBFj004508 for ; Mon, 20 Sep 2010 17:30:12 -0700 Received: from iwn35 (iwn35.prod.google.com [10.241.68.99]) by kpbe15.cbf.corp.google.com with ESMTP id o8L0Tuk8006662 for ; Mon, 20 Sep 2010 17:30:10 -0700 Received: by iwn35 with SMTP id 35so6041516iwn.23 for ; Mon, 20 Sep 2010 17:30:10 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1285020801.30653.5.camel@dcbw.foobar.com> References: <1285020801.30653.5.camel@dcbw.foobar.com> Date: Mon, 20 Sep 2010 17:30:09 -0700 Message-ID: Subject: Re: mac80211: Why probe after each scan? From: Paul Stewart To: Dan Williams Cc: linux-wireless@vger.kernel.org, Johannes Berg , Sam Leffler , "Berg, Johannes" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: But mac80211 also does beacon loss detection. I'd much prefer more aggressive (shorter timeout) beacon loss parameters (perhaps configured that way only after end-of-scan, although I believe in general the timeout is rather generous even for the normal case) than to require round-trips with the AP just to find out if it's there. For the most part, I think beacons do the job of AP presence detection fairly well. -- Paul On Mon, Sep 20, 2010 at 3:13 PM, Dan Williams wrote: > On Fri, 2010-09-17 at 20:01 -0700, Paul Stewart wrote: >> I found a small bit of behavior related in some vague way to >> connection monitoring: ?During the scan-completed notification >> (ieee80211_mlme_notify_scan_completed) we call >> ieee80211_restart_sta_timer() on all our interfaces, which in turn >> queues up the &ifmgd->monitor_work, which does a probe request of our >> AP. ?Why should we do a probe request of your associated AP every time >> a scan completes? ?Wouldn't the other active monitoring schemes (like >> beacon loss) be sufficient for a "scan finished" condition? > > One reason I can think of is to quickly determine whether your AP is > still around and active given that you may have just been off-channel > for a significant period of time. ?Not all drivers background scan yet. > But with any sane driver, you'd have already sent your "no longer in > powersave mode" NULL packet to the AP right after finishing the scan, so > perhaps the probe is redundant. > > Dan > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-wireless" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at ?http://vger.kernel.org/majordomo-info.html >