Virtual networks in an integrated time-triggered architecture

Depending on the physical structuring of large distributed safety-critical real-time systems, one can distinguish federated and integrated system architectures. This paper investigates the communication services of an integrated system architecture, which combines the complexity management advantages of federated systems with the functional integration and hardware benefits of an integrated approach. A major challenge is the need to accommodate the communication services to the different types of integrated application subsystems that range from ultra-dependable control applications (e.g., an x-by-wire system) to non safety-critical applications such as multimedia or comfort systems. In particular, the encapsulation of the communication activities of different application subsystems is required not only to prevent error propagation from non safety-critical application subsystems to higher levels of criticality, but also to facilitate complexity management and permit independent development activities. This paper introduces virtual networks as the encapsulated communication infrastructure of an application subsystem in the integrated DECOS architecture. Virtual networks are constructed as overlay networks on top of the time-triggered communication system of a base architecture. Each virtual network runs a corresponding communication protocol that is determined either by a legacy platform or selected to meet the requirements of the application subsystem. Encapsulation mechanisms ensure that the temporal properties of each virtual network are known a priori and independent from the communication activities in other virtual networks. By assigning to each application subsystem a dedicated virtual network and by ensuring that the virtual network abstractions hold also in the case of faults, the integrated architecture supports the benefits of a federated system, such as fault isolation, complexity management, independent development, and intellectual property protection. In addition, virtual networks promise massive cost savings through the reduction of physical networks and reliability improvements with respect to wiring and connectors.