Is the round-trip time correlated with the number of packets in flight?

ABSTRACT

TCP uses packet loss as a feedback from the network to adapt its sending rate. TCP keeps increasing its sending rate as long as no packet loss occurs (unless constrained by buffer size). Alternative congestion avoidance techniques (CATs) have been proposed to avoid such "aggressive" behavior. These CATs use simple statistics on observed round-trip times and/or throughput of a TCP connection in response to variations in congestion window size. These CATs have a supposed ability to detect queue build-up.The objective of this paper is to question the ability of these CATs to reliably detect queue build-up under real network conditions. For this purpose, the sample coefficient of correlation between round-trip time and the number of packets in flight is analyzed for 14,218 connections over 737 Internet paths. These coefficients of correlation were extracted from a set of tcpdump traces collected by Vern Paxson.The coefficients of correlation measured confirm that the correlation between RTT and window size is often weak.

REFERENCES

• 1: J. Andren, M. Hilding, and D. Veitch. Understanding end-to-end internet traffic dynamics. In Proc. IEEE Globecom Internet Mini-Conference, Sydney, Australia, pages 1118--1122, Nov. 1998.
• 2: Saad Biaz , Nitin H. Vaidya, Heterogeneous data networks: congestion or corruption?, 1999
• 3: S. Biaz and N. H. Vaidya. Distinguishing congestion losses from wireless transmission losses: A negative result. In IEEE 7th IC3N'98, Lafayette, LA USA.
• 4: Saad Biaz , Nitin H. Vaidya, Is the Round-trip Time Correlated with the Number of Packets in Flight ?, Texas A & M University, College Station, TX, 1999
• 5: Lawrence S. Brakmo , Sean W. O'Malley , Larry L. Peterson, TCP Vegas: new techniques for congestion detection and avoidance, Proceedings of the conference on Communications architectures, protocols and applications, p.24-35, August 31-September 02, 1994, London, United Kingdom
• 6: U. Hengartner, J. Bolliger, and T. Gross. TCP Vegas revisited. In IEEE Infocom'00, Mar. 2000.
• 7: V. Jacobson, Congestion avoidance and control, Symposium proceedings on Communications architectures and protocols, p.314-329, August 16-18, 1988, Stanford, California, United States
• 8: R. Jain, A delay-based approach for congestion avoidance in interconnected heterogeneous computer networks, ACM SIGCOMM Computer Communication Review, v.19 n.5, p.56-71, Oct. 1989 [doi>10.1145/74681.74686]
• 9: Jim Martin , Arne Nilsson , Injong Rhee, Delay-based congestion avoidance for TCP, IEEE/ACM Transactions on Networking (TON), v.11 n.3, p.356-369, June 2003 [doi>10.1109/TNET.2003.813038]
• 10: Jim Martin , Arne Nilsson , Injong Rhee, The incremental deployability of RTT-based congestion avoidance for high speed TCP Internet connections, Proceedings of the 2000 ACM SIGMETRICS international conference on Measurement and modeling of computer systems, p.134-144, June 18-21, 2000, Santa Clara, California, United States
• 11: Jitendra Padhye , Victor Firoiu , Don Towsley , Jim Kurose, Modeling TCP throughput: a simple model and its empirical validation, Proceedings of the ACM SIGCOMM '98 conference on Applications, technologies, architectures, and protocols for computer communication, p.303-314, August 31-September 04, 1998, Vancouver, British Columbia, Canada
• 12: Vern Edward Paxson, Measurements and analysis of end-to-end Internet dynamics, University of California at Berkeley, Berkeley, CA, 1998
• 13: V. Paxson. Private email, Jan. 1999.
• 14: W. Richard Stevens, TCP/IP illustrated (vol. 1): the protocols, Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 1993
• 15: Kishar Shridharbhai Trivedi, Probability and Statistics with Reliability, Queuing and Computer Science Applications, Prentice Hall PTR, Upper Saddle River, NJ, 1982
• 16: Zheng Wang , Jon Crowcroft, A new congestion control scheme: slow start and search (Tri-S), ACM SIGCOMM Computer Communication Review, v.21 n.1, p.32-43, Jan. 1991 [doi>10.1145/116030.116033]

INDEX TERMS

Primary Classification:
  C. Computer Systems Organization
  C.4 PERFORMANCE OF SYSTEMS

Additional Classification:
  C. Computer Systems Organization
  C.2 COMPUTER-COMMUNICATION NETWORKS
      C.2.2 Network Protocols

General Terms:
Documentation, Experimentation

Keywords:
TCP, congestion control, congestion predictors, congestion window size, correlation, roundtrip time