From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Heffner Subject: Re: [PATCH] make _minimum_ TCP retransmission timeout configurable Date: Wed, 29 Aug 2007 18:52:48 -0400 Message-ID: <46D5F8C0.4080801@psc.edu> References: <5640c7e00708291432q6acde704od52247647a6b453@mail.gmail.com> <20070829.144656.104048365.davem@davemloft.net> <46D5F32F.2070502@hp.com> <20070829.153503.18295527.davem@davemloft.net> <46D5F7C8.8090806@psc.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: rick.jones2@hp.com, ian.mcdonald@jandi.co.nz, netdev@vger.kernel.org To: David Miller Return-path: Received: from mailer1.psc.edu ([128.182.58.100]:56445 "EHLO mailer1.psc.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758315AbXH2Wwx (ORCPT ); Wed, 29 Aug 2007 18:52:53 -0400 In-Reply-To: <46D5F7C8.8090806@psc.edu> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org John Heffner wrote: >> What exactly causes such a huge delay? What is the TCP measured RTO >> in these circumstances where spurious RTOs happen and a 3 second >> minimum RTO makes things better? > > I haven't done a lot of work on wireless myself, but my understanding is > that one of the biggest problems is the behavior link-layer > retransmission schemes. They can suddenly increase the delay of packets > by a significant amount when you get a burst of radio interference. It's > hard for TCP to gracefully handle this kind of jump without some minimum > RTO, especially since wlan RTTs can often be quite small. (Replying to myself) Though F-RTO does often help in this case. -John