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

Michał Grabowski, Robert Marek Janowski


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.

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Postel, J., (1981), Transmission control protocol, IETF RFC 793.

Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., Schooler, E., (2002), SIP: Session Initiation Protocol. IETF RFC 3261.

Postel, J., (1980), User Datagram Protocol, IETF RFC 768.

Shelby, Z., Hartke, K., Bormann, C., (2014), The Constrained Application Protocol (CoAP), IETF RFC 7252, 2014.

Rathod, V. J. and Tahiliani, M. P., (2020a), Geometric Sequence Technique for Effective RTO Estimation in CoAP, In IEEE International Conference on Advanced Networks and Telecommunications Systems (ANTS), New Delhi, India, 2020, pp. 1-6, doi: 10.1109/ANTS50601.2020.9342748.

Rathod, V. J., Krishnam, S., Kumar, A., Baraskar, G., Tahiliani, M. P., (2020b), Effective RTO estimation using Eifel Retransmission Timer in CoAP," In IEEE International Conference on Electronics, Computing and Communication Technologies (CONECCT), Bangalore, India, 2020, pp. 1-6, doi: 10.1109/CONECCT50063.2020.9198559.

Loukili, A., Wijesinha, A. L., Karne, R. K., Tsetse, A. K., (2012), TCP's Retransmission Timer and the Minimum RTO, In 21st International Conference on Computer Communications and Networks (ICCCN), Munich, Germany, 2012, pp. 1-5, doi: 10.1109/ICCCN.2012.6289266.

Psaras, I., Tsaoussidis, V. (2007), The TCP Minimum RTO Revisited. In: Akyildiz, I.F., Sivakumar, R., Ekici, E., Oliveira, J.C.d., McNair, J. (eds) NETWORKING 2007, Ad Hoc and Sensor Networks, Wireless Networks, Next Generation Internet. NETWORKING 2007. Lecture Notes in Computer Science, vol 4479. Springer, Berlin, Heidelberg.

Ma, L., Barner, K. E., Arce, G.R., (2006), Statistical analysis of TCP's retransmission timeout algorithm, IEEE/ACM Transactions on Networking, 14, 2, (April 2006), 383-396.

Ma, L., Arce, G., Barner, K., (2004), TCP Retransmission Timeout Algorithm Using Weighted Medians, IEEE Signal Processing Letters, vol. 11, No. 6, June 2004 pp. 569-572.

Janowski, R., Grabowski, M., Arabas, P, (2020), New Heuristics for TCP Retransmission Timers. In: Burduk, R., Kurzynski, M., Wozniak, M. (eds) Progress in Computer Recognition New Heuristics for TCP Retransmission Timers Systems. CORES 2019. Advances in Intelligent Systems and Computing, vol 977. Springer, Cham.

Nikzad, N., Jamshidi, K., Bohlooli, A., Faqiry, F. M., (2022), An accurate retransmission timeout estimator for content-centric networking based on the Jacobson algorithm, Digital Communications and Networks, Volume 8, Issue 6, 2022, Pages 1085-1093, ISSN 2352-8648,

Jacobson, V., Congestion avoidance and control, (1988), In Proc. SIGCOMM'88, Stanford, CA, Aug. 1988, pp. 314-329.

Pereyra, M. C., Ward, L. A., (2010), Harmonic Analysis. From Fourier to Wavelets, Student Mathematical Library, 2010, ISBN 978-0-8218-7566-7.


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