From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kristian Evensen" Subject: Strange TCP behavior over HSDPA Date: Mon, 28 Dec 2009 13:56:22 +0100 Message-ID: <4b38aaf7.0f67f10a.0624.6a06@mx.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Return-path: Received: from mail-ew0-f219.google.com ([209.85.219.219]:51278 "EHLO mail-ew0-f219.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751322AbZL1M4Z (ORCPT ); Mon, 28 Dec 2009 07:56:25 -0500 Received: by ewy19 with SMTP id 19so1746559ewy.21 for ; Mon, 28 Dec 2009 04:56:24 -0800 (PST) Content-Language: no Sender: netdev-owner@vger.kernel.org List-ID: 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