The power-series algorithm applied to cyclic polling systems

Polling Systems;Queueing Theory;operations research

A method for analyzing the performance aspects of the fault-tolerance mechanisms in FDDI

The ability of error recovery mechanisms to make the Fiber Distributed Data Interface (FDDI) satisfy real-time performance constraints in the presence of errors is analyzed. A complicating factor in these analyses is the rarity of the error occurrences, which makes direct simulation unattractive. Therefore, a fast simulation technique, called injection simulation, which makes it possible to analyze the performance of FDDI, including its fault tolerance behavior, was developed. The implementation of injection simulation for polling models of FDDI is discussed, along with simulation result

A vehicle-to-infrastructure communication based algorithm for urban traffic control

We present in this paper a new algorithm for urban traffic light control with mixed traffic (communicating and non communicating vehicles) and mixed infrastructure (equipped and unequipped junctions). We call equipped junction here a junction with a traffic light signal (TLS) controlled by a road side unit (RSU). On such a junction, the RSU manifests its connectedness to equipped vehicles by broadcasting its communication address and geographical coordinates. The RSU builds a map of connected vehicles approaching and leaving the junction. The algorithm allows the RSU to select a traffic phase, based on the built map. The selected traffic phase is applied by the TLS; and both equipped and unequipped vehicles must respect it. The traffic management is in feedback on the traffic demand of communicating vehicles. We simulated the vehicular traffic as well as the communications. The two simulations are combined in a closed loop with visualization and monitoring interfaces. Several indicators on vehicular traffic (mean travel time, ended vehicles) and IEEE 802.11p communication performances (end-to-end delay, throughput) are derived and illustrated in three dimension maps. We then extended the traffic control to a urban road network where we also varied the number of equipped junctions. Other indicators are shown for road traffic performances in the road network case, where high gains are experienced in the simulation results.Comment: 6 page

Iterative approximation of k-limited polling systems

The present paper deals with the problem of calculating queue length distributions in a polling model with (exhaustive) k-limited service under the assumption of general arrival, service and setup distributions. The interest for this model is fueled by an application in the field of logistics. Knowledge of the queue length distributions is needed to operate the system properly. The multi-queue polling system is decomposed into single-queue vacation systems with k-limited service and state-dependent vacations, for which the vacation distributions are computed in an iterative approximate manner. These vacation models are analyzed via matrix-analytic techniques. The accuracy of the approximation scheme is verified by means of an extensive simulation study. The developed approximation turns out be accurate, robust and computationally efficient

Collaborative workflow management using service oriented approach

Collaborative workflow systems in large logistics companies require a well integrated information systems infrastructure and a strong communication network to meet major new challenges and opportunities. Agile infrastructure, enabled by integration, can have substantial impact on the overall success of a business, these IT integration requirements are expanding considerably with the advent of ebusiness; utilizing B2B (Business to Business) web services and P2P (Partner to Partner) e-commerce. This paper deals with change management of collaborative workflow in such consortia and proposes integration architecture for synchronization of these changes through the process of service modules integration where by existing workflow systems are adapted to the changes. This paper will describe conceptual framework and implementation strategy resulting in new collaborative workflow adaptation

De-perimeterisation as a cycle: tearing down and rebuilding security perimeters

If an organisation wants to secure its IT assets, where should the security mechanisms be placed? The traditional view is the hard-shell model, where an organisation secures all its assets using a fixed security border: What is inside the security perimeter is more or less trusted, what is outside is not. Due to changes in technologies, business processes and their legal environments this approach is not adequate anymore.\ud This paper examines this process, which was coined de-perimeterisation by the Jericho Forum.\ud In this paper we analyse and define the concepts of perimeter and de-perimeterisation, and show that there is a long term trend in which de-perimeterisation is iteratively accelerated and decelerated. In times of accelerated de-perimeterisation, technical and organisational changes take place by which connectivity between organisations and their environment scales up significantly. In times of deceleration, technical and organisational security measures are taken to decrease the security risks that come with de-perimeterisation, a movement that we call re-perimeterisation. We identify the technical and organisational mechanisms that facilitate de-perimeterisation and re-perimeterisation, and discuss the forces that cause organisations to alternate between these two movements

On reliability modeling and evaluating in cloud services system

A typical system of reliability of cloud services with a cloud management system is explored. The proposed model is service-oriented and hierarchical. It includes two phases of query maintenance: 1) time-out and overflow; 2) execution. The model is described by the system of Chapman-Kolmogorov equations. The final stage of the process is protection of user requests and results of tasks execution. An approach to cloud data security is proposed which, unlike traditional approaches, guarantees confidentiality and security of information even at compromising the provider of cloud service or its infrastructure.Досліджується типова система надійності хмарних сервісів з системою керування хмарами. Пропонована модель сервісно-орієнтована та ієрархічна. Вона включає дві фази обслуговування запитів: 1) попередня (тайм-аут і переповнення); 2) виконання. Модель описується системою рівнянь Чепмена-Колмогорова. Останній етап процесу ˗ захист запитів користувачів та виконання завдань. Запропоновано підхід до захисту даних хмарних даних, який, на відміну від традиційних підходів, гарантує конфіденційність та безпеку інформації, навіть при компрометації постачальника хмарних сервісів або його інфраструктури