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The analytical framework for optimizing TCP retransmission algorithm based on adjustment of its EWMA parameters

Grabowski Michał, Janowski Robert

International Journal of Electronics and Telecommunications

2024

Vol. 70, No. 1

253--260

In this paper we derive mathematical description of TCP (Transmission Control Protocol) retransmission probability based on Jacobson’s smoothing algorithm that belongs to EWMA (Exponentially Weighted Moving Average) category. This description is parametrized on the probability density function (pdf) of RTT (Round Trip Time) samples and α, β – two primary parameters of Jacobson’s algorithm. Although it is not a close form expression, it is formulated as an effective algorithm that let us to explicitly calculate the values of RTO (Retransmission Time Out) probability as a function of α, β and the pdf of RTT samples. We achieve the effectiveness of this approach by applying smart discretization of the state space and replacement of continuous functions with discrete approximate equivalents. In this way, we mitigate the cardinality of discrete distributions we deal with that results in linear (n+m) instead of multiplicative (n⋅m) growth of computational complexity. We provide the evaluation of RTO probability for a wide set of α, β parameter values and differently shaped Normal and Laplace pdfs the RTT samples are taken from. The obtained numerical results let us to draw some conclusions regarding the choice of optimal values of α, β parameters as well as the impact of pdf the RTT samples are taken from.

Which control chart is the best for the particleboard industry: Shewhart, CUSUM or EWMA?

Kurt Rifat, Karayilmazlar Selman

Drewno : prace naukowe, doniesienia, komunikaty

2021

vol. 64, nr 208

95--117

In this study, control charts were prepared using data received from a particleboard manufacturer to determine the factors that impair quality, and the most suitable control charts for the company were specified accordingly. The study material consisted of the tensile strength values of boards taken from a factory over three months. Shewhart, CUSUM and EWMA control charts were used for variable quantities to achieve the targeted quality level. It was concluded from the research that interdependent and independent evaluation of the data observed during particleboard manufacturing was required; therefore, the combined use of CUSUM and Shewhart control charts was proposed.