Hierarchical AED Scheduling Algorithm for Real-Time Networks

Earlier studies have observed that in moderately-loaded real-time systems, using an earliest deadline policy to schedule tasks results in the fewest missed deadlines. However, when the real-time system is overloaded an earliest deadline schedule performs worse than most other policies. This is due to the earliest deadline giving the highest priority to the tasks that are close to missing their deadlines, thus delaying other transactions that might still be able to meet their deadline. In this research, an enhanced priority assignment algorithm is presented, called the Adaptive Earliest Deadline (AED), which features a feedback control mechanism that detects overload conditions and modifies packet priority assignments accordingly. Using a detailed simulation model, the performance of AED is compared and analyzed with Earliest Deadline First (EDF). Furthermore, an enhanced AED algorithm called the Hierarchical AED is proposed in a manner in which it obtains a better packet-serving performance by using the concept of priority based on Quality of Service (QoS) of network traffic rather than using a random priority assignment when doing the packet group assignment. Finally, the performance of Hierarchical AED scheduling algorithm is compared with both EDF and the AED scheduling algorithms under the same operating environment.