This paper deals with real-time dependable systems required to achieve the best usage of the resources even under adverse circumstances as transient overloads or component failures. Various possible trade-offs among the different application requirements must be considered to allow a flexible management of system resources. On the basis of a simple formulation of the concept of value in real-ti...

In this paper, we report our recent work on closed form solutions to the blocking and dropping probability in wireless cellular networks with handoff. First, we develop a performance model of a cell in a wireless network where the effect of handoff arrival and the use of guard channels are included. Fast recursive formulas for the loss probabilities of new calls and handoff calls are given. Alg...

Distributed software is usually structured in layers, with some kind of operational control or user interface tasks as the topmost layer, making requests to various layers of servers. Client Server systems and ODP (Open Distributed Processing) systems such as DCE, ANSA and CORBA are structured this way, as are distributed transaction processing systems. Performance and dependability are the two...

In this paper, we discuss a case study performed for validating a Natural Language (NL) based software requirements specification (SRS) in terms of completeness, consistency, and fault-tolerance. A partial verification of the Guidance and Control Software (GCS) Specification is provided as a result of analysis using three modeling formalisms. Zed was applied first to detect and remove ambiguity...

Non-stop operation, despite the occurrence of faults, is a key requirement for highly-reliable, real-time systems , such as aircraft and nuclear reactor controller computers. Reconnguration is commonly used to mean the process of transforming the execution structure of a system from one state to another when a fault occurs. We identiied two types of reconngura-tion: fault-tolerating reconngurat...

This paper describes a measurement-based performability model based on error and resource usage data collected on a multiprocessor system. A method for identifying the model structure is introduced and the resulting model is validated against real data. Model development from the collection of raw data to the estimation of the expected reward is described. Both normal and error behavior of the ...