1. Iperf Quick Mode Ajay Tirumala & Les Cottrell

2. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Iperf QUICK Mode Problem – Current TCP apps cannot detect when they are out of slow-start Bandwidth measurement apps have to run for a considerable time to counter the effects of slow-start. Plot from Brian Tierney, LBL

3. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala

4. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Iperf Quick Mode Solution – Use Web100 to detect the end of slow-start – Measure bandwidth for a small period after slowstart (say 1s). – This should save about 90% of estimation time and traffic generated. Ideas evolved out of an email exchange between Tom Dunigan, Brian Tierney & Les Cottrell

5. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Detecting end of Slow-start Outline – Determine a sampling period for Congestion Window – Detect the absence of exponential increase every RTT – Handle pathological cases Connection may not get out of slow-start – Multiple slow-starts Connection may have a very small bandwidth-delay product. – E.g. localhost transfers, with latency in nano-seconds. – At present, it handles Reno and Vegas It should handle Net100/Floyd stacks with minor modifications.

6. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala The Quick mode Algorithm Initialize Iperf sockets and initialize Web100 connection for the for the Iperf socket. Start Web100 data collection thread – This will indicate when the connection is definitely out of slow- start Detect the end of slow-start in the data transfer thread – If congestion window does not stabilize, do NOT report QUICK mode results Measure bandwidth for 1s (or user specified time) after slow-start Only client requires Web100, can use unmodified iperf server

7. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Results Slow-starts can be – From 0.2 seconds for low-latency networks – Up to 5 sec for long haul high bandwidth networks. Maximum gains here by using Iperf in QUICK mode. – Unless, we use it in quick mode, we can never be sure that the connection is out of slow-start Performed tests on dialup links (as receiver) through hundreds of Mbits/s links with over 150ms RTT SLAC – CERN, 160ms Note 2 slow starts, 4 secs to reach stability

8. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Results SLAC-Japan 140ms * 350Mbits/s ~ 6MByte) SLAC-TRIUMF RTT 72 ms. congested link

9. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Results Differs with throughputs for running iperf for 20s by less than 10% Traffic reduction 92% Measure ment time reduced by 94%

10. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Web100 experiences A must use tool (We are fans) User-APIs can be improved Behaves well for a sampling time of 20ms.

11. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Possible areas to investigate Integrate with BW tests. Perform tests with slow-senders (e.g. dialup). Empirical estimates immediately after slow-start : – Using RTT and rate of increase of congestion window.

12. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Links Iperf Quick mode : – http://www-iepm.slac.stanford.edu/bw/iperf_res.html http://www-iepm.slac.stanford.edu/bw/iperf_res.html Documentation and results of tests with all IEPM-BW managed nodes available from this link.

13. Sep 12, 2002 Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala Other stuff… Miniperf is a small Iperf-like program written to – Monitor user-specified Web100 variable(s) – Allows setting window sizes and test times Can include parallel thread functionality – Generate graphs (rate based, sum based) – Generate HTML Created a single Iperf version to run on IPv4/v6 (Web100)/(no Web1000).

14. Thank you!!!