From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarek Poplawski Subject: Re: Strange TCP behavior over HSDPA Date: Tue, 29 Dec 2009 08:30:50 +0000 Message-ID: <20091229083050.GA7209@ff.dom.local> References: <4b38aaf7.0f67f10a.0624.6a06@mx.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: Kristian Evensen Return-path: Received: from mail-fx0-f225.google.com ([209.85.220.225]:59343 "EHLO mail-fx0-f225.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751229AbZL2Ia6 (ORCPT ); Tue, 29 Dec 2009 03:30:58 -0500 Received: by fxm25 with SMTP id 25so5077061fxm.21 for ; Tue, 29 Dec 2009 00:30:56 -0800 (PST) Content-Disposition: inline In-Reply-To: <4b38aaf7.0f67f10a.0624.6a06@mx.google.com> Sender: netdev-owner@vger.kernel.org List-ID: On 28-12-2009 13:56, Kristian Evensen wrote: > Hello, > > I have a laptop running Ubuntu 9.04 with the 2.6.32.2-kernel and the machine > connects to the internet using HSDPA. When transferring files (from the same > server) using TCP I notice that the connection often experience severe drops > in throughput. Often, it takes over a second for the (fast) retransmission > to arrive. > > First I thought this might be due to poor network conditions, but when > testing tunnels (L2TP and PPTP) I noticed that the throughput was more > stable and the average higher. It seems like the retransmission is sent and > arrives quicker than without tunnels. The drops last for a shorter period of > time and does not affect the performance that much. Based on my > understanding of the tunneling protocols, they offer no reliability for data > and according to my ISP UDP and TCP packets are treated equally. > > I have performed several experiments (adjusting the MTU, MSS and running the > tests from different places) trying to figure out why tunnels perform better > than without tunnels, but I have not been able to come up with an answer. > The different experiments all give the same result. So my question is, has > anyone experienced anything similar or have an idea as to why the tunnels > perform better? > > The HSDPA-modems I have used are the Huawei E220 and Sierra Wireless Aircard > 880u. If anyone is interested in looking at the packet dumps, they can be > found here [1] and here [2]. [1] is without tunnels and a typical packet > loss is shown at packet 1705, while [2] is without tunnels and a typical > packet loss is shown at 3381. > > Thanks in advance for any help, > Kristian > > [1] - http://heim.ifi.uio.no/~kristrev/hsdpa-captures/loss_hsdpa.pcap > [2] - http://heim.ifi.uio.no/~kristrev/hsdpa-captures/loss_hsdpa_tunnel.pcap The most obvious difference seems to be the SACK option used in [2], so maybe something on the route breaks it (without tunnels). Jarek P.