Current network situation with its limited resources and excessive users' demands reveals the potential necessity for revolutionary organization and management of these resources. Efficient and effective resource scheduling significantly reduces queuing delay which considered as crucial particularly for sensitive packets such as real-time application. This study investigates in the main four categories of scheduling mechanism; FCFS, Priority Queuing, Fair Queuing and Class Based Queuing. It proofs by using OPNET that Fair Queuing is the best in term of providing higher QoS for Realtime application.