Аннотация:We consider a multi-server queueing system in which primary customers arrive according to a regenerative flow. The system has m stochastically identical servers. Service times are independent identically distributed random variables and have an arbitrary distribution. An arriving customer finding one or more servers idle obtains service immediately. Customers who find all servers busy go directly to the orbit from which repeat attempts to get into idle server. Two classes of such systems are considered. For the first class the rate of retrial requests depends on the number of customers on the orbit and for the second class the rate is a constant.Based on the synchronization of the input flow and an auxiliary service process we establish the necessary and sufficient stability conditions for the models of both classes. Limit theorems for the number of customers on the orbit in the heavy traffic situation are established.Approaches to statistical analysis of the system parameters when the number of customers on the orbit is observed are presented. Some applications are also given.