From owner-freebsd-questions Mon Jul 29 5:43:19 2002 Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id EB22B37B401; Mon, 29 Jul 2002 05:43:07 -0700 (PDT) Received: from fnord.ir.bbn.com (FNORD.IR.BBN.com [192.1.100.210]) by mx1.FreeBSD.org (Postfix) with ESMTP id 84A0043E3B; Mon, 29 Jul 2002 05:43:07 -0700 (PDT) (envelope-from gdt@ir.bbn.com) Received: by fnord.ir.bbn.com (Postfix, from userid 10853) id C53333EC0; Mon, 29 Jul 2002 08:43:06 -0400 (EDT) To: Dan Pelleg Cc: freebsd-mobile@freebsd.org, freebsd-questions@freebsd.org Subject: Re: Thinkpad overheating when talking to a D-Link wireless AP References: <15666.52258.20053.339128@gs166.sp.cs.cmu.edu> From: Greg Troxel Date: 29 Jul 2002 08:43:06 -0400 In-Reply-To: Dan Pelleg's message of "Mon, 15 Jul 2002 09:20:34 -0400" Message-ID: Lines: 48 X-Mailer: Gnus v5.7/Emacs 20.7 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG The 802.11 specification (now freely available, but a bit hard to read - so I may be slightly off in terminology here since I don't have it handy) describes several ways an access point can operate. All of these are part of "BSS" mode and I believe are typically handled in firmware without the knowledge of the driver. The most basic is the Distributed Coordination Function (DCF), in which a station (STA) transmits frames to the AP after performing Clear Channel Assessment (basically listen for below-threshold energy in the channel). There are randomized backoffs for retransmission. This is basically a contention mechanism. Then, there is the Point Coordination Function (PCF), where the AP controls who gets to transmit. This is either associatied with or implemented by the "Contention-Free Period", where the AP controls who transmits. Basically the AP sends a packet to a station and lets the station send a reply packet with the ack. The AP can also poll stations to see if they have traffic. So an AP could run in a mode where most of the time is PCF, which can get much higher channel usage. This all interacts with power saving, which can work with both modes. (getting fuzzier) There is an announcement period where stations indicate that they have traffic (or the AP says what STAs it has traffic for), followed by time to exchange traffic. This enables a STA to shut down its receiver if the announcement traffic (from the AP) told it that there was no traffic for it. APs never shut down. I am pretty sure this works in both DCF and PCF. This is the basis of power saving mode - a STA informs the AP on association that it wants to be able to go into doze mode, and wakes up to hear the beacons from the AP. If there is no traffic for that STA, it goes back to sleep until the next beacon. I think the interval is on the order of multiple tens of milliseconds, and that this is an AP configurable value (in theory; not sure about particular APs). So, I would wonder if that AP either does not implement power-saving mode (I believe this is not optional, but I don't remember), or if it is configured off. Is your card in power-save mode, and does it get hot with the Lucent aps if you turn power-save mode off? If you really want to understand this, I recommend that you read the 802.11 spec (802.11b is just a 'Higher-rate PHY in the 2.4 GHz band' - the stuff above is in the base 802.11 document), but be warned that it is not easy reading. Then, try the dachd0den labs prism2dump, or get tcpdump.org tcpdump to decode 802.11 management frames, so you can see what's going on. Greg Troxel To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message