The primary role of admission control in quality of service enabled networks is to control the amount of traffic injected into the network so that congestion is avoided and certain performance requirements are met. We consider engineered and provisioned IP differentiated services networks able to support realtime traffic and we address the placement of admission control at the traffic aggregation points of the network, and the granularity of the admission control logic. Regarding the first issue, we show that sophisticated admission control schemes that take into account statistical multiplexing gains need only be employed at the first traffic aggregation points. Further downstream, peak rate admission control will suffice. With respect to the second issue, we propose a framework for admission control, which involves a combined approach of traffic descriptor and measurement-based techniques.