Formalization and Correctness of the PALS Architectural Pattern for Distributed Real-Time Systems

Many Distributed Real-Time Systems (DRTS), such as integrated modular avionics systems and distributed control systems in motor vehicles, are made up of a collection of components communicating asynchronously among themselves and with their environment that must change their state and respond to environment inputs within hard real-time bounds. Such systems are often safety-critical and need to be certi???ed; but their certi???cation is currently very hard due to their distributed nature. The Physically Asynchronous Logically Synchronous (PALS) architectural pattern can greatly reduce the design and veri???cation complexities of achieving virtual synchrony in a DTRS. This work presents a formal speci???cation of PALS as a formal model transformation that maps a synchronous design, together with a set of performance bounds of the underlying infrastructure, to a formal DRTS speci???cation that is semantically equivalent to the synchronous design. This semantic equivalence is proved, showing that the formal veri???cation of temporal logic properties of the DRTS can be reduced to their veri???cation on the much simpler synchronous design. An avionics system case study is used to illustrate the usefulness of PALS for formal verification purposes.unpublishednot peer reviewe

Fault-tolerant real-time communication in FDDI-based networks

The first high-speed network to meet the Safenet standard’s bandwidth requirements, the fiber distributed data interface needs help to meet Safenet’s fault-tolerance requirement. A network management mechanism uses online and offline components to work around multiple faults. Users are increasingly deploying high-speed networks in distributed computer systems. These networks may have stringent real-time and fault-tolerance requirements. FDDI (fiber distributed data interface) 1 is a 100-Mbps local area network based on a token ring media access control protocol defined by ANSI and OSI standards. It has built-in provisions for fault-tolerance and real-time communications. Because of this, FDDI has been adopted as the underlying backbone network for the Safenet standard. Safenet is the US Departmen