Pitfalls in the fluid modeling of RTT variations in window-based congestion control

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Deterministic delay differential equation models, where the packet traffic is modeled as a fluid, are widely used to study congestion control algorithms in the Internet. In this paper, we point out some pitfalls in such fluid modeling of window flow control algorithms. Specifically, we argue that the modeling assumptions used to capture the variability in the RTT (due to queue length fluctuations) may play a critical role in our ability to design stable algorithms. We study two scenarios to illustrate the dramatic impact of RTT modeling. We first consider TCP-Reno with RED, and show that assuming that the RTT is a constant (when it is actually time-varying) leads to conservative parameter choices, i.e., the system continues to be stable even with variable RTT. On the other hand, for the recently proposed Stabilized Vegas, we show the following result: while the network can be stabilized under the constant RTT assumption, there is no choice of parameters that would stabilize the system when the RTT variations are taken into account! Interestingly, such problems do not arise if the congestion-control mechanisms at the end-users are rate-based.

Original languageEnglish (US)
Title of host publicationProceedings - IEEE INFOCOM 2005. The Conference on Computer Communications - 24th Annual Joint Conference of the IEEE Computer and Communications Societies
EditorsK. Makki, E. Knightly
Number of pages11
StatePublished - 2005
EventIEEE INFOCOM 2005 - Miami, FL, United States
Duration: Mar 13 2005Mar 17 2005

Publication series

NameProceedings - IEEE INFOCOM
ISSN (Print)0743-166X


Country/TerritoryUnited States
CityMiami, FL


  • Congestion Control
  • RED
  • Round Trip Delay
  • Stabilized Vegas
  • TCP Vegas

ASJC Scopus subject areas

  • General Computer Science
  • Electrical and Electronic Engineering


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