Comparative performance analysis of directed flow control for real-time SCI

The distributed nature of routing and flow control in a register-insertion ring topology complicates priority enforcement for real-time systems. Two divergent approaches for priority enforcement for ringbased networks are reviewed: a node-oriented scheme called Preemptive Priority Queue and a ring-wide arbitration approach dubbed TRAIN. This paper introduces a hybrid protocol named Directed Flow Control that combines nodeand ring-oriented flow control to yield greater performance. A functional comparison of the three protocols as implemented on the Scalable Coherent Interface (SCI) is presented, followed by performance results obtained through high-fidelity modeling and simulation.