From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ey0-f171.google.com (mail-ey0-f171.google.com [209.85.215.171]) (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 D4772200049 for ; Wed, 15 Jun 2011 14:11:11 -0700 (PDT) Received: by eydd26 with SMTP id d26so497585eyd.16 for ; Wed, 15 Jun 2011 14:35:05 -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=69ZAjma20GJAbStXaPawDIeBxjJk61vzT5sB3lqk640=; b=uc+AX/DdawD2eZOsQ7Ngm4DC0zhS6sPqjznJDh45muLO4l9X4VOBoJ1MaZXey4/Yip +lZ0Tcae0rqwLBxDb6OEYB2GkgHm6rnsMVHCJdxr2IS5DWIQ5FveR7lUhiM8tSbFv9iy eUZEO7VAwYeHNiStuuim5b9cbWadSedq13gM4= 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=R1dRAkd/iDdPI9x9EERkUIbqu2Orv8hFujZbJA/V1faFC7n5RKXF612PqfCQlWSbxh xbcoWd7jU/pnnCRuvvVTMTS5r4m1Y2h+cM3Z6PrIBs/1yWICFiDhc7YqpdfyUKBC4wSl yA9MNDTVRC2kKHnsBrLbMS7VbRQZGT+FO1pQ0= Received: by 10.213.7.139 with SMTP id d11mr62898ebd.43.1308173705045; Wed, 15 Jun 2011 14:35:05 -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 b19sm778471eec.8.2011.06.15.14.35.01 (version=TLSv1/SSLv3 cipher=OTHER); Wed, 15 Jun 2011 14:35:03 -0700 (PDT) Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: text/plain; charset=us-ascii From: Jonathan Morton In-Reply-To: Date: Thu, 16 Jun 2011 00:34:59 +0300 Content-Transfer-Encoding: quoted-printable Message-Id: <1286F6FC-3F03-4A5E-A21D-5FA940E31EFB@gmail.com> References: To: Dave Taht X-Mailer: Apple Mail (2.1084) Cc: bloat Subject: Re: [Bloat] wireless software retry with ECN? 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: Wed, 15 Jun 2011 21:11:12 -0000 On 15 Jun, 2011, at 9:43 pm, Dave Taht wrote: > When you have to retry sending a packet in swretry at a wireless > driver (mac802.11?) level, marking it as 'congested' seems to make = sense. >=20 > If you are going to make heroic efforts to deliver packets in the > first place, you might as well tell the receiver of your heroism. This actually makes sense, because one of the major causes of a packet = retry is noise - and other wifi networks sharing the same airspace (or = indeed other APs for the same network in the same large room) look a lot = like noise to the receiver. OTOH, a single retry might not be enough to justify this - it could be = due to burst noise or short-term fading (ie. the user walked behind a = pillar). But then again, a single ECN marked packet shouldn't have a = large effect on the TCP. On the gripping hand, due to the definition of ECN, this would require = that hardware does not retry (or, alternately, only retries once) any = packets that are not ECN enabled. This is because the ECN RFC says that = routers must drop packets which would otherwise have been marked if they = are not ECN enabled (and thus cannot be marked). Reducing TTL on each retransmission *sounds* like a good idea too, but = might require more detailed analysis. How many retransmits are = typically attempted by current hardware? Do we really want to reduce = the number of retries based on how far away in the internet they came = from? Do we really want to reduce the ability of heroically-transmitted = packets to reach their ultimate destination abroad? This isn't really = what TTL is designed for. - Jonathan