Advanced real-time scheduling using the IEEE 802.5 token ring

An approach for scheduling the IEEE 802.5 token ring for hard real-time applications is presented that not only guarantees deadlines for synchronous class messages, but also greatly reduces asynchronous class response times. Highly responsive guaranteed service is introduced for alert class asynchronous messages. Conventional use of the IEEE 802.5 token ring provides synchronous communication services using time-domain multiplexing (TDM) while relegating asynchronous class message services to background status. An algorithmic-based scheduling approach is presented that supports a priori schedulability determination for arbitrary synchronous message sets without the costly time-line development, testing, and tuning associated with TDM techniques. This capability allows the IEEE 802.5 to support dynamic, adaptive and reconfigurable run-time environments where the inflexibility of TDM would be prohibitive. Advanced real-time scheduling applied to the IEEE 802.5 token ring greatly enhances the responsiveness of asynchronous class messages while still maintaining guaranteed service for the synchronous class