Bratiichuk, M.S., Chechelnitsky , A.A. and Usar, I.Y. 2020. M/M/1 retrial queueing model with variable service rate. Ukrains’kyi Matematychnyi Zhurnal. 72, 3 (Mar. 2020), 355-365. DOI:https://doi.org/10.37863/umzh.v72i3.813.