From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Long-term TCP connections suffer on high-latency links. Date: Thu, 29 Jul 2004 22:01:50 -0700 Sender: netdev-bounce@oss.sgi.com Message-ID: <4109D63E.5070006@candelatech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: To: "'netdev@oss.sgi.com'" Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org I have been running a TCP connection over a link with 2 seconds round-trip-time. It started off well, about 16Mbps in both directions (cwnd trained up to 2100 after a few seconds). After several hours of running, it is now doing only about 2.2Mbps in one direction, and 3.4Mbps in the other direction. I have watched the cwnd slowly increasing by one every 2-5 seconds (it is at 440 on one side and 655 on the other as I type). Occasionally, the cwnd drops in half or maybe even goes to zero. The un-acked packets is always == snd_cwnd. My suspicion is that for connections needing a cwnd of 2000 or so, the cwnd does not grow nearly fast enough after the connection has been established for a while. My naive suggestion would be to increase cwnd by a certain percentage instead of a fixed number (1). But, TCP has been around a long while, and surely other people have noticed things like this, so what am I missing? Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com