Abstract. The paper considers the retrial queueing system M /M /1 /0 with combined discipline of service, namely, a customer from the orbit is served in its turn, but in case of a free channel an arrival from the original flow is serviced immediately. The author obtained the expressions for state probabilities as well as the ergodicity conditions. The system is compared with the Lakatos type system.

Keywords: queueing system, retrial queueing system, orbit, cycling-waiting queueing system, combined discipline of service, stability condition of system.