Responsive, deterministic IEEE 802.5 token ring scheduling

Abstract

This paper presents a novel approach for scheduling the IEEE 802.5 token ring. This approach not only guarantees deadlines for synchronous class messages, but also dramatically reduces asynchronous class response times. Further, highly responsive guaranteed service is introduced for alert class asynchronous messages. Conventional use of the IEEE 802.5 token ring standard guarantees synchronous communication services using Time Domain Multiplexing (TDM) techniques while relegating asynchronous class message services to background status. The result is poor responsiveness. Further, the TDM schedules tend to be fragile and difficult to modify and extend. This paper presents an algorithmic-based scheduling approach that supportsa priori schedulability determination for arbitrary synchronous message sets without the costly development, testing, and tuning of TDM schedules. This capability allows the IEEE 802.5 standard to support dynamic, adaptive, and reconfigurable run-time environments where the inflexibility of TDM would be prohibitive. Advanced real-time scheduling theory is applied to the IEEE 802.5 token ring standard and dramatically enhances asynchronous class messages' responsiveness while still maintaining guaranteed service for the synchronous class. The result is a highly responsive real-time ring that can form the backbone of predictable, stable, and extendible real-time systems.