Publish-Subscribe Dynamics
In addition to designing the system avionics network can be architected to focus on data rather than devices. Systems that use point-to-point data transfer through message passing or other mechanisms tend to be brittle and can break when data, code, or devices change. Specifically, point-to-point data transfers mean each instrument has to have knowledge of another instrument’s specific needs, its data, and its interfaces. This inherent awareness of the data endpoints represents a significant issue in the maintenance of individual applications and the system in general over the life of the avionics platform. Instead, by focusing on data definition, it is possible to abstract both code and instruments away from the details of the network endpoints, providing the foundation of a robust and scalable system. This is done by employing a publish-subscribe architecture where a source publishes its data, and the data is delivered to any device subscribing to that data. This architecture enables a data-centric design approach, where each device decides the data it needs, rather than worrying about the instrument’s configuration that generated the data. Network usage can be reduced through the use of multicast data delivery and tuning of Quality of Services (QoS) parameters on the data streams — a necessity for critical avionics systems. The publish-subscribe framework provides highly efficient scalability, enabling avionics integrators to add additional instruments and subsystems without having to worry about modifying their communication code.

A publish-subscribe architecture can be implemented with middleware that complies with the Object Management Group’s Distributed Data Service (DDS) standard, which supports real-time response, high performance, and comprehensive control via QoS. By abstracting data producers and consumers from low-level communication details, DDS allows distributed systems to be easily designed, implemented, and maintained. A standards-based solution that combines a high-performance RTOS with data-centric distributed middleware has significant advantages for the life cycle of an avionics system. The result is an avionics network that is technically easier to create and maintain over time, while also providing a standards-based platform for high performance and reliability. It can deliver greater safety and responsiveness as aircraft mission needs evolve. The lower complexity of this standards- based RTOS and middleware solution minimizes the cost of maintenance over the airframe lifecycle, both because of the abstraction of the details of applications and instruments and because of the reduced requirements for systemlevel testing when adding or modifying devices. Because performance and reliability are maintained as the devices on the network increase, cost should prove predictable, even with an expected airframe life measured in decades.

This article was written by Dr. Heidi Schubert, Senior Applications Engineer, at Real Time Innovations in Santa Clara, CA; and Sonia Leal, Senior Product Manager, at LynuxWorks in San Jose, CA. For more information, contact Dr. Schubert at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it , or visit http://info.hotims.com/10968-403.