General AIMD congestion control

  • Authors:
  • Y. R. Yang;S. S. Lam

  • Affiliations:
  • -;-

  • Venue:
  • ICNP '00 Proceedings of the 2000 International Conference on Network Protocols
  • Year:
  • 2000

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Abstract

Instead of the increase-by-one decrease-to-half strategy used in TCP for congestion window adjustment, we consider the general case such that the increase value and decrease ratio are parameters. That is, in the congestion avoidance state, the window size is increased by /spl alpha/ per window of packets acknowledged and it is decreased to /spl beta/ of the current value when there is congestion indication. We refer to this window adjustment strategy as general additive increase multiplicative decrease (GAIMD). We present the (mean) sending rate of a GAIMD flow as a function of /spl alpha/, /spl beta/, loss rate, mean round-trip time, mean timeout value, and the number of packets acknowledged by each ACK. We conducted extensive experiments to validate this sending rate formula. We found the formula to be quite accurate for a loss rate of up to 20%. We also present a simple relationship between /spl alpha/ and /spl beta/ for a GAIMD flow to be TCP-friendly, that is, for the GAIMD flow to have approximately the same sending rate as a TCP flow under the same path conditions. We present results from simulations in which TCP-friendly GAIMD flows (/spl alpha/=0.31, /spl beta/=7/8) compete for bandwidth with TCP Reno flows and with TCP SACK flows, on a DropTail link as well as on a RED link. We found that the GAIMD flows were highly, TCP-friendly. Furthermore, with /spl beta/ at 7/8 instead of 1/2, these GAIMD flows have reduced rate fluctuations compared to TCP flows.