All the new OS's (IE Windows7) automatically adjust TCP window size. Personally I've never found those website speed test to be that accurate on fast connections (over 15Mbps full duplex). The only way to really confirm bandwidth is by running IPERF. Robert Glover wrote:
Adjust your TCP window size.
-----Original Message----- From: "Murphy, William" <William.Murphy@uth.tmc.edu> Date: Thu, 29 Apr 2010 10:53:01 To: nanog@nanog.org<nanog@nanog.org> Subject: Edu versus Speakeasy Speedtest
I work for an Edu with multi-gigabit Internet connectivity and I get questions from users saying "Why am I only getting 14Mb when I run this speed test?" I have got to believe that the various Internet speed tests (Speakeasy or dslreports) are rate limited to prevent someone from shutting them down. I am able to get 300-400Mb running from a PC inside my network to NDT servers located on Internet2, so that tells me my border and internal network is healthy. Can someone on this list shed some light regarding reliability and accuracy of these various speed tests especially for an Edu with lots'o bandwidth? Thanks.
Bill Murphy
University of Texas Health Science Center - Houston