“…The waiting time distribution, the time a request spends in the orbit, is very complicated problem in the retrial queue system theory. Different approaches to the investigation of the waiting time can be found in Artalejo, Chakravarthy, Lopez-Herrero [1], Artalejo, Gomez-Corral [4], Choi, Chang [6], Falin, Artalejo [8], Gharbi, Dutheillet [14], Sudyko, Nazarov, Sztrik [27], Tóth, Bérczes, Sztrik [28], Zhang, Feng, Wang [29] for finite retrial group of sources and Chakravarthy, Dudin [7], Falin, Fricker [9], Falin [1,10,12], Gomez-Corral, Ramalhoto [15], Neuts [20], Nobel, Tijms [25], Lee, Kim, Kim [18] for infinite number of sources.…”