Abstractions, Architecture, Mechanisms, and a Middleware for Networked Control

We focus on the mechanism half of the policy-mechanism divide for networked control systems, and address the issue of what are the appropriate abstractions and architecture to facilitate their development and deployment. We propose an abstraction of ldquovirtual collocationrdquo and its realization by the software infrastructure of middleware. Control applications are to be developed as a collection of software components that communicate with each other through the middleware, called Etherware. The middleware handles the complexities of network operation, such as addressing, start-up, configuration and interfaces, by encapsulating application components in ldquoShellsrdquo which mediate component interactions with the rest of the system. The middleware also provides mechanisms to alleviate the effects of uncertain delays and packet losses over wireless channels, component failures, and distributed clocks. This is done through externalization of component state, with primitives to capture and reuse it for component restarts, upgrades, and migration, and through services such as clock synchronization. We further propose an accompanying use of local temporal autonomy for reliability, and describe the implementation as well as some experimental results over a traffic control testbed.