Return-path: Received: from smtp.nokia.com ([192.100.122.233]:39887 "EHLO mgw-mx06.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752798Ab0CQGHu (ORCPT ); Wed, 17 Mar 2010 02:07:50 -0400 Subject: Re: [RFC PATCHv2 0/2] mac80211: cfg80211: Roam trigger support From: Juuso Oikarinen To: ext Johannes Berg Cc: "linux-wireless@vger.kernel.org" In-Reply-To: <1268776349.8918.9.camel@jlt3.sipsolutions.net> References: <1268657751-1042-1-git-send-email-juuso.oikarinen@nokia.com> <1268776349.8918.9.camel@jlt3.sipsolutions.net> Content-Type: text/plain; charset="UTF-8" Date: Wed, 17 Mar 2010 08:02:52 +0200 Message-ID: <1268805772.10120.603.camel@wimaxnb.nmp.nokia.com> Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Tue, 2010-03-16 at 22:52 +0100, ext Johannes Berg wrote: > On Mon, 2010-03-15 at 14:55 +0200, Juuso Oikarinen wrote: > > To implement good performance WLAN roaming, it is not sufficient to start > > scanning for other available AP's only after the currently serving association > > is lost. > > > > The entity controlling the roaming will need to get indication of a > > deteriorating WLAN connection in order to start preparing for roaming already > > before the serving association is lost. This way, it can roam to a better AP > > perhaps even before the serving association becomes too bad in quality. > > > > These patches propose an implementation facilitating this using a simple RSSI > > threshold and hysteresis approach. > > > > These patches add a nl80211 interface for simply configuring a rssi threshold > > and hysteresis value to facilitate very basic connection quality monitoring. > > > > For the triggering, these patches currently rely on HW support, host based > > triggering is not implemented, but could be added later if needed. > > I'm curious. How does the HW/firmware do this? > In my testing on some hw, the beacon RSSI fluctuated wildly, so you'd > have to set the hysteresis pretty high. The HW/firmware can be configured with parameters related to averaging, which will smoothen the worst of the fluctuation at least between single frames. Still, there is the WLAN tendency of a very steep RSSI curve, so we'll probably end up with a relatively high hysteresis. Figuring out good values for the config is still to-be-done. -Juuso > johannes >