A slot swapping protocol for time-critical internetworking

This paper proposes an architecture and communication protocol called the Slot Swapping Protocol which is used to interconnect, by means of a backbone, different subsystems that generate and consume real-time data. The proposed communication architecture fits well into the general Computer Integrated Manufacturing (CIM) model, thus representing an appealing solution for FieldBus interconnection in factory automation systems. Inspired by the concept of session swapping, the Slot Swapping Protocol makes a step forward in slotted rings by including explicit time constraints in traffic scheduling, as it assigns a dynamic priority to slots and uses an Earliest Deadline First-based swapping policy. The paper describes the communication protocol, discusses three slot swapping approaches and presents a set of experiments characterizing the protocol's ability to meet traffic deadlines in several working conditions.