1. 1 How to Identify the Speed Limiting Factor of a TCP Flow E2EMON 2006 Vancouver Mark Timmer April 3, 2006 Co-authors: Pieter-Tjerk de Boer and Aiko Pras

2. 2 How to Identify the Speed Limiting Factor of a TCP Flow Motivation Related work Possible factors Overview: identifying the limiting factors One factor in-depth Measurement results Conclusions E2EMON, April 3, 2006 Contents

3. 3 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Motivation Surfnet: 1 Gbit 10 Gbit Upgrades still useful? Approach: Identify speed limiting factor

4. 4 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Related work Y. Zhang, L. Breslau, V. Paxson, and S. Shenker, “On the characteristics and origins of internet flow rates”, Proceedings of SIGCOMM’02 M. Siekkinen, G. Urvoy-Keller, E.W. Biersack, and T. En-Najjary, “Root cause analysis for long-lived tcp connections”, Proceedings of CoNEXT’05

5. 5 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Speed limiting factors of a TCP flow

6. 6 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Overview: identifying the limiting factors Data repository of packet traces Information directly available: –Arrival time –IP header (source, destination) –TCP header (port numbers, sequence number, acknowledgment number, size of receive window) Information calculated: –Number of outstanding bytes –Achieved throughput

7. 7 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Application layer limitations (1) Slow sender limitation Identification –Measure idle period percentage –Careful when receive window is empty Note: We only consider flows measured at the sending side

8. 8 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Application layer limitations (2) Slow receiver limitation Identification –Measure how often the receive window decreases

9. 9 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Application layer limitations (3) Application protocol limitation Identification –Measure how often an ACK contains data Note: We only consider flows sending data one-way

10. 10 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Network limitation (1) Limited by loss / retransmission ‘TCP Friendly formula’

11. 11 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow –Large buffers –Entire receive window stored –Injecting more packets more delay Network limitation (2) Limited by delay

12. 12 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow TCP buffers limitations The receive buffer limitation The send buffer limitation

13. 13 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Peaks In-depth: the receive window limitation

14. 14 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Measurement results Category% flows% bytes Undetermined20 – 4010 – 20 Network20 – 3030 – 40 Send buffer 0 – 10 Receive buffer10 – 1510 – 20 Slow sender20 – 3020 – 40 Slow receiver0 – 5 Application protocol 0 – 100 – 1

15. 15 E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow Conclusions Upgrading network still useful However, many flows limited by buffers Recommentations: –Perform statistical analyses –Develop tool to ‘fix’ TCP-buffer limited flows –Detect changes of limiting factor in time

16. 16 Questions? E2EMON, April 3, 2006 How to Identify the Speed Limiting Factor of a TCP Flow