Abstract In customer-intensive public services, the value provided by the service increases with the time which the servicer spends with the customer, and the waiting time of following customers have to extend on the other hand. Then how to maximize the social welfare? The M/M/1 model is introduced base on the ‘homogeneous customers’ and ‘two classes of customers with different unit-waiting-cost (UC)’, respectively. The results demonstrate that the optimal diversity policy is only to service the customers with low-UC; when the high-UC is increasing as the low-UC fixed, the social welfare of the optimal diversity policy will increase to maximum, and the social welfare of the policy servicing all arriving customers will decrease; the service provider should control the customer arriving rate in any scenarios when the potential arriving rate is higher than the threshold, otherwise the social welfare will decrease because of congestion.
