From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ew0-f43.google.com (mail-ew0-f43.google.com [209.85.215.43]) (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 DDCFD2004FD for ; Sun, 29 May 2011 06:54:40 -0700 (PDT) Received: by ewy20 with SMTP id 20so1518351ewy.16 for ; Sun, 29 May 2011 07:10:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:subject:mime-version:content-type:from :in-reply-to:date:cc:content-transfer-encoding:message-id:references :to:x-mailer; bh=NPFVcsSabifd1crGNAL50rq6O2koQNFSeJlv8lKELmQ=; b=dnbwqq/TWzBnFOIEpv2CIJdInfTe7P/dVh28AYqmmUXL/KHygdTbR8mfKHPnAefHsH 88KAzkDV/cr9/Bx1plLgh9rYtvgL3KSJZ+RBQCS0eb7OG6xbmrMNIp/CJ5psEcTqEfWI 5/6p5wWgVldFOz4fhXzzX7UXH+RwrcgQGeGSY= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:mime-version:content-type:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to:x-mailer; b=FVzm9xv359QA0yE8Me3sSAHhLcY8V9bc7ntguueWZ2P690JupGC0jQQH3We68yfrv4 uzwS1Fo46tcaQg4c0nD8hRXGdUuVCA02IIJ3yr4zOvmqfQogbKIWBDRsSEUYf3jmU3f9 8ck1q0pV4mlPPsMCNSJEUbfdnUx9mW7iEKA/A= Received: by 10.14.1.71 with SMTP id 47mr1456435eec.128.1306678225258; Sun, 29 May 2011 07:10:25 -0700 (PDT) Received: from [192.168.239.42] (xdsl-83-150-84-172.nebulazone.fi [83.150.84.172]) by mx.google.com with ESMTPS id m14sm2559162eeh.12.2011.05.29.07.10.23 (version=TLSv1/SSLv3 cipher=OTHER); Sun, 29 May 2011 07:10:24 -0700 (PDT) Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: text/plain; charset=us-ascii From: Jonathan Morton In-Reply-To: Date: Sun, 29 May 2011 17:10:20 +0300 Content-Transfer-Encoding: quoted-printable Message-Id: References: To: Dave Taht X-Mailer: Apple Mail (2.1084) Cc: bloat Subject: Re: [Bloat] tiny monsters: multicast packets X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 29 May 2011 13:54:41 -0000 On 29 May, 2011, at 4:23 pm, Dave Taht wrote: > In my last 2 months of travel, I have seen multicast packets, such as = ARP, DHCP, MDNS, and now babel, all failing far, far, far more often = than is desirable. I have seen DHCP fail completely for hours at a time, = I've seen ARP take dozens of queries to resolve.=20 And the irony is that the lower speed is specifically chosen for = multicast in order to make sure all clients in range can hear them = reliably. Broadcast packets are not supposed to be large ones, but = wireless framing must add a lot of fixed overhead. Given that the AP surely knows which hosts are attached to it at any = given time, and what link rate they are currently sustaining, surely a = saner design would have been either: 1) Broadcast the packet at the lowest link rate for all known attached = hosts. 2) Unicast the packet to each attached host in turn, at that host's = current link rate. The latter sounds wasteful, but would still be a win on 802.11g in = compatibility mode. It also turns the AP into a star-topology hub, so = hosts would send their broadcast packets by unicast to the AP, which = would repeat them. But presumably the brokenness is now baked firmly into the standard, and = is therefore inescapable. So the workaround is to isolate the broadcast = domains of wired networks and wireless networks by making the home = router into... a router. Wireless on one subnet, wired on another, and = so ARP between the two turns into ARP to the router alone - much more = scalable. I should check whether my Airport Base Station already supports that. - Jonathan