Design of a Deterministic Service Switch for Avionics Networks

Abstract

Avionics full-duplex switched Ethernet, with its capability of delivering deterministic latency at low deployment costs, represents a major advance for avionics communication systems. However, avionics full-duplex switched Ethernet does not eliminate contentions at network switches, which may result in an uncontrolled increase in end-to-end latencies, and hence limit the potential of this technology. The use of time to pace packet transmission and forwarding (that is, the adoption of pipeline forwarding) has been demonstrated to avoid contentions at switching nodes in wide-area communication networks, thus being potentially attractive also for avionics networks in general, and avionics full-duplex switched Ethernet in particular. However, questions might arise concerning the actual feasibility of such an approach in the avionics domain due to the possibly high costs required to deploy packet switches able to operate according to a very precise time schedule, which is necessary to respect the stringent delivery deadlines of avionics systems. This paper focuses on the development of a pipeline forwarding switch, showing how simple design guidelines allow a general-purpose symmetric multiprocessor architecture (such as modern personal computers) to offer deterministic and low latency delivery, thus being able to satisfy avionics requirements. The paper also describes a real implementation of a pipeline forwarding switch prototype, based on a dual-processor personal computer and the FreeBSD operating system.