From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-iy0-f171.google.com (mail-iy0-f171.google.com [209.85.210.171]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id CC9D0200346 for ; Thu, 8 Dec 2011 04:46:27 -0800 (PST) Received: by iaen33 with SMTP id n33so4065615iae.16 for ; Thu, 08 Dec 2011 04:46:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=1mBKc8WhRAswD2D6CAonv7qxG4NuFVjOK3Y8UhtUYXU=; b=t/gaw4jeLgWfusWNKiruNmOBkMNBLYdhg70M572ixF9taiB+EELUcbUX9S8PdxiYTw uMJg5OhgtSJBwkrrm0CD5LlydckZFyqajshhXvi7h3pvP/Skv08Qxyft9XKSVbbXNDQB W+xoTd2F+ucs1Gw0+prIF4aIDUnPsHnJyXSdA= MIME-Version: 1.0 Received: by 10.50.140.1 with SMTP id rc1mr3852711igb.25.1323348387192; Thu, 08 Dec 2011 04:46:27 -0800 (PST) Received: by 10.231.204.83 with HTTP; Thu, 8 Dec 2011 04:46:27 -0800 (PST) In-Reply-To: References: Date: Thu, 8 Dec 2011 13:46:27 +0100 Message-ID: From: Dave Taht To: david@lang.hm Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: cerowrt-devel@lists.bufferbloat.net Subject: Re: [Cerowrt-devel] Coping with wireless-n [#305] X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 08 Dec 2011 12:46:28 -0000 On Thu, Dec 8, 2011 at 1:25 PM, wrote: > On Thu, 8 Dec 2011, Dave Taht wrote: > >> On Thu, Dec 8, 2011 at 12:51 PM, =A0 wrote: >>> >>> On Thu, 8 Dec 2011, Dave Taht wrote: >> >> >>> this puzzles me. >>> >>> splitting 2.4G and 5G into different different networks (broadcast >>> domains) >>> is a huge win. cince I can't find any open implementation fo band >>> steering, >>> this requires putting the two bands on different SSIDs. >> >> >> Oh, god no, I'm not dropping that. Having those split AND off the wired >> network is staying in... >> >>> but I don't understand why there is a big problem with G and N sharing >>> the >>> same SSID. >> >> >> Because you can fully FQ G, and if you do that to N, it messes up >> aggregation. > > > I don't recognize the term "FQ". Fair Queue http://info.iet.unipi.it/~luigi/qfq/ in this case. > > when you say it messes up aggregation, do you mean combining two channels > togeather for higher throughput or something else? No, the way the driver is structured it swallows as many packets as are aggregatable for a given destination, then ships them. If you instead try to do the right thing - which is to break up packet bursts into as tiny pieces as possible, aggregation goes to heck. What you want to do is aggregate fair queued packets for a given destination, at a size that will fit (up to 64 packets or 64kbytes) at the rate the wireless interface is running at. As a result nobody does FQ, nor AQM, on wireless n, where it is so desparately needed. > > I was assuming that if you are running a mized network you only use a sin= gle > channel for N. If you are using multiple channels for N they should be a > separate SSID, just from the fact that you are using two channels for N b= ut > only one for G (which one would be the question) One channel for both N and G in this case. Only one radio for 5ghz. > >>> >>> there is some >> >> >> Some? > > > some, but it's an unavoidable feature of wireless communication. You can > consider turning off some modulation types, but since the clients > automatically fall back to slower modulation types when there is a proble= m, > the result will be failed connections. To give you an idea, at 5ghz I'm capable with cerowrt at achieving 150Mbits with TCP - in the clean air here. At 2.4, it's rare I can get more than 20, and fairly often much less than t= hat. Any given test I run regarding wireless simply is not repeatable if I do it on 2.4ghz. I can usually 'hear' more than 30 access points at my apt, as another example. > > now, this may still be the right thing to do, because the failback to a > slower modulation type works well for weak signal situations, but in a hi= gh > density situation (which is basically every 2.4G deployment in the real > world nowdays), taking longer to send the same data just means that you a= re > more vunerable to another transmitter clobbering you, so it actually > decreases reliability. yes, minstrel rocks. > > David Lang > > >>> grief with having different speeds on the same channel, but >>> only in that the same amount of data will take longer to transmit >>> (causing >>> problems with predicting how long the queue is in terms of time as it >>> will >>> vary on the destintation), but even if you stick with G for example, it >>> can >>> transmit at 54, 48, 36, 24, 18, 12, 6, 1 Mb/s. adding N just adds some >>> higher speeds to this. If the devices are configured sanely, they shoul= d >>> be >>> transmitting the header for a G frame to reserve the air time and then >>> sending the N frame inside of that. this has a slight overhead compared >>> to a >>> pure N network, but it doesn't matter if the G network is on the same >>> SSID >>> or on a different one, the problem is sharing the airtime on the channe= l. >> >> >> It's a packet scheduler test more than anything else. >> >>> David Lang >> >> >> >> >> > --=20 Dave T=E4ht SKYPE: davetaht US Tel: 1-239-829-5608 FR Tel: 0638645374 http://www.bufferbloat.net