Model checking medium access control for sensor networks

We describe verification of S-MAC, a medium access control protocol designed for wireless sensor networks, by means of the PRISM model checker. The S-MAC protocol is built on top of the IEEE 802.11 standard for wireless ad hoc networks and, as such, it uses the same randomised backoff procedure as a means to avoid collision. In order to minimise energy consumption, in S-MAC, nodes are periodically put into a sleep state. Synchronisation of the sleeping schedules is necessary for the nodes to be able to communicate. Intuitively, energy saving obtained through a periodic sleep mechanism will be at the expense of performance. In previous work on S-MAC verification, a combination of analytical techniques and simulation has been used to confirm the correctness of this intuition for a simplified (abstract) version of the protocol in which the initial schedules coordination phase is assumed correct. We show how we have used the PRISM model checker to verify the behaviour of S-MAC and compare it to that of IEEE 802.11

Software Reliability Modeling using Fault Tree Analysis and Stochastic Petri Nets

This thesis estimates the performance of software system using Stochastic Petri Nets (SPN) and Fault Tree Analysis (FTA).This paper explains how a working Petri net model and fault tree model is developed for a soft real time system. Evaluating reliability of software at the early stage of the development is become key concern for most of the organization. Assessing the reliability at early stage helps in removing many bugs and hence improving the efficiency of the architecture. Reliability is computed based on failure rates of systems by using a modified architecture based approach for reliability modelling.Fault Tree Analysis is a method for identifying and documenting the combinations of lower-level software events that allow a top-level event (or root node) to occur. But fault trees are event oriented. The dependency between the components can not be easily incorporated in the model. Similarly redundancies,time delay conditions and other dynamic behaviour can not be easily modelled using fault trees, since they are static in nature. SPN model is used to counter the problems of Fault Trees. A ATM system is taken as an example to model the system in both fault tree and stochastic petri net

A formalism for describing and simulating systems with interacting components.

This thesis addresses the problem of descriptive complexity presented by systems involving a high number of interacting components. It investigates the evaluation measure of performability and its application to such systems. A new description and simulation language, ICE and it's application to performability modelling is presented. ICE (Interacting ComponEnts) is based upon an earlier description language which was first proposed for defining reliability problems. ICE is declarative in style and has a limited number of keywords. The ethos in the development of the language has been to provide an intuitive formalism with a powerful descriptive space. The full syntax of the language is presented with discussion as to its philosophy. The implementation of a discrete event simulator using an ICE interface is described, with use being made of examples to illustrate the functionality of the code and the semantics of the language. Random numbers are used to provide the required stochastic behaviour within the simulator. The behaviour of an industry standard generator within the simulator and different methods of number allocation are shown. A new generator is proposed that is a development of a fast hardware shift register generator and is demonstrated to possess good statistical properties and operational speed. For the purpose of providing a rigorous description of the language and clarification of its semantics, a computational model is developed using the formalism of extended coloured Petri nets. This model also gives an indication of the language's descriptive power relative to that of a recognised and well developed technique. Some recognised temporal and structural problems of system event modelling are identified. and ICE solutions given. The growing research area of ATM communication networks is introduced and a sophisticated top down model of an ATM switch presented. This model is simulated and interesting results are given. A generic ICE framework for performability modelling is developed and demonstrated. This is considered as a positive contribution to the general field of performability research

Quantification and compensation of the impact of faults in system throughput

Performability relates the performance (throughput) and reliability of software systems whose normal behaviour may degrade owing to the existence of faults. These systems, naturally modelled as discrete event systems using shared resources, can incorporate fault-tolerant techniques to mitigate such a degradation. In this article, compositional faulttolerant models based on Petri nets, which make its sensitive performability analysis easier, are proposed. Besides, two methods to compensate existence of faults are provided: an iterative algorithm to compute the number of extra resources needed, and an integer-linear programming problem that minimises the cost of incrementing resources and/or decrementing fault-tolerant activities. The applicability of the developed methods is shown on a Petri net that models a secure database system. Keywords Performability, fault-tolerant techniques, Petri nets, integer-linear programmin

Performance Evaluation of CORBA Concurrency Control Service Using Stochastic Petri Nets

The interest in performance evaluation of middleware systems is increasing. Measurement techniques are still predominant among those used to carry out performance evaluation. However, performance models are currently being defined due to their flexibility, precision and facilities to carry out capacity planning activities. This paper presents stochastic Petri net models for performance evaluation of the CORBA Concurrency Control Service (CCS), which mediates concurrent access to objects. In order to validate the proposed models, CCS performance results obtained using those models are then compared against ones obtained through actual measurements.The interest in performance evaluation of middleware systems is increasing. Measurement techniques are still predominant among those used to carry out performance evaluation. However, performance models are currently being defined due to their flexibility, precision and facilities to carry out capacity planning activities. This paper presents stochastic Petri net models for performance evaluation of the CORBA Concurrency Control Service (CCS), which mediates concurrent access to objects. In order to validate the proposed models, CCS performance results obtained using those models are then compared against ones obtained through actual measurements