Simple Integrated Media Access (SIMA) is a differentiated service scheme based on drop preference bits in every packet. The basic idea of the SIMA is to maximize the exploitation of network resources with a simple control scheme while keeping the ratios of QoS levels offered to different flows unchanged under changeable traffic conditions with a aid of novel charging scheme. This paper examines the potential problems of the SIMA concept and then proposes some possible solutions in order to enhance the service efficiency. The basic idea of Differentiated Services is to provide customers with different kind of service according to their needs and willingness to pay. Each IP packet carrying DiffServ traffic will be equipped with information how the network should treat the data packet. For this purpose, six bits in the header of IP packet are reserved for conveying DiffServ information. Simple Integrated Media Access (SIMA) introduces a complete scheme with detailed access node as well a...