Admission control is an important tool for resource management in systems that provide service to a heterogeneous set of customers. In these situations, it may be efficient to deny service to an arriving customer although there is available capacity, in order to preserve the service resource for anticipated future arrivals of customers of a higher priority class. Such models have wide applicability in telecommunications (calling center design and management, mobile telephony, etc.), revenue management and manufacturing management.

In this talk we consider a service system with many identical servers and no waiting buffer (loss system). Customers are classified into two types. The arrivals of the two types follow independent Poisson processes and the service times are exponentially distributed with generally class dependent service rates. Each customer generates a profit depending on his or her type. Upon arrival, the system manager must decide whether to accept the incoming customer or deny service. Customers arriving to a full system are lost. The objective is to find a dynamic policy of admission that maximizes the long-run expected average profit per unit time.

We show that the optimal admission policy has a threshold structure. In addition we discuss the issue of existence and identification of a preferred customer class, i.e., a class that is always admitted when there are free servers. Finally we consider extensions of the basic model to situations of random service profits and batch customer arrivals.