Scheduling is the dynamic process of allocating a shared resource to multiple parallel users in order to optimize some desirable performance metrics. Metrics of interest include: maximization of system throughput, minimization of packet delay and jitter, and the provision of fairness. Scheduling is a key mechanism in RRM and operates in the medium access control (MAC) layer. Only three things can happen to the transmission medium of a multiuser network: resource hogging, resource clogging, or equitable resource sharing. Without a MAC protocol, the desirable third option can hardly occur. In the following we discuss some general aspects of OS, propose a generalized OS design framework, discuss future trends of OS, and list some open issues in OS design.