Scripts for Bandwidth Measurement

The information available from active tests such as BWCTL can be enhanced by embedding them in scripts which collect TCP stats before and even during the BWCTL test.

UNIX/Linux Scripts

• BWCTL Script by Toby Rodwell (new version required for Linux 2.6.19) From an idea by Baruch Even (the Hamilton Institute) this script captures 'netstat' statisitics before and after a BWCTL run, and during the run periodically executes the command /usr/sbin/ss which shows socket state, including (importantly) the value for cwnd and ssthresh. Informal, non-rigorous testing indicates that in order to avoid reducing the achieveable throughput then (on a Pentium 4 3GHz, 512MB RAM device) the 'ss' command should not be run more frequently than every 0.1 or 0.2s
  • Scipt usage:- tcptest <target BWCTL server> <test duration in seconds> <'ss' check interval in seconds>
  • Example command:- tcptest sri.geant.net 60 0.2
  • Example results of script

– Main.TobyRodwell - 25 Jun 2006