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Next generation wireless networks are expected to support multi-rate multimedia services, including wideband services, and to have smaller cell structures like micro/pico cells. Smaller cells increase the handoff traffic drastically and wideband services cause severe network fluctuations with their frequent handoffs. As a result, it is a challenge to provide stable QoS in wireless networks. In addition, some wideband services suffer from poor QoS under congestion, where wideband services have less chance of getting enough resources compared to narrowband services. We introduce a region, a logical cell, defined as a minimal set of cells, which enables stable call control in wireless traffic conditions. Then, we propose a two-level call admission control (CAC) mechanism, in which CAC is performed in a region as well as in a cell. The simulation results show that the proposed CAC mechanism not only guarantees QoS under any traffic conditions, but also improves the QoS. The CAC also achieves service fairness by reducing QoS differences among the services.