Khalid Alnowibet

Nonstationary analysis of circuit-switched communication networks

Circuit-switched communication networks have been analyzed extensively in the stationary case, i.e. where the arrival and/or service rates are independent of time. In this paper, we study a circuit-switched network where the rates of external arrivals at the network are time-dependent functions. The circuit-switched network is modelled as a nonstationary queueing network with population constraints, which is analyzed approximately in order to obtain the blocking probability functions. Using this method we model two circuit-switched networks, namely, a traffic-groomed tandem optical network and a single-orbit LEO satellite network.

Nonstationary analysis of the loss queue and of queueing networks of loss queues

We present an iterative scheme based on the fixed-point approximation method, for the numerical calculation of the time-dependent mean number of customers and blocking probability functions in a nonstationary queueing network with multi-rate loss queues. We first show how the proposed method can be used to analyze a single-class, multi-class, and multi-rate nonstationary loss queue. Subsequently, the proposed method is extended to the analysis of a nonstationary queueing network of multi-rate loss queues. Comparisons with exact and simulation results showed that the results are consistently close to the exact results and they are always within simulation confidence intervals.

The Nonstationary Loss Queue: A Survey

The nonstationary loss queue is of great interest since the arrival rate in most communication systems varies over time. In view of the difficulty in solving the nonstationary loss queue, various approximation methods have been developed. In this paper, we review several of these approximation methods and present a new technique, the fixed point approximation (FPA) method. Numerical evidence points to the fact that the FPA method gives the exact solution.

Probabilistic OWA distances applied to asset management

Average distances are widely used in many fields for calculating the distances between two sets of elements. This paper presents several new average distances by using the ordered weighted average, the probability and the weighted average. First, the work presents the probabilistic ordered weighted averaging weighted average distance (POWAWAD) operator. POWAWAD is a new aggregation operator that uses distance measures in a unified framework between the probability, the weighted average and the ordered weighted average (OWA) operator that considers the degree of importance that each concept has in the aggregation. The POWAWAD operator includes a wide range of particular cases including the maximum distance, the minimum distance, the normalized Hamming distance, the weighted Hamming distance and the ordered weighted average distance (OWAD). The article also presents further generalizations by using generalized and quasi-arithmetic means forming the generalized probabilistic ordered weighted averaging weighted average distance (GPOWAWAD) operator and the quasi-POWAWAD operator. The study ends analysing the applicability of this new approach in the calculation of the average fixed assets. Particularly, the work focuses on measuring the average distances between the ideal percentage of fixed assets that the companies of a specific country should have versus the real percentage of fixed assets they have. The illustrative example focuses on the Asian market.

A quorum queueing system with unreliable server and restricted admission

We consider in this paper a bulk service, or quorum, queueing system. The server is unreliable and may break down while providing service. The admission to the system is controlled and some arrivals may be denied admission. The queueing process is studied and relevant performance measures, such as the mean number of customers in the system, the mean duration of the idle period, busy period, and busy cycle, are obtained. These measures are then used to design an optimal management policy for the system where the optimal quorum size is sought. The effect of relevant system parameters on the optimal quorum size and optimal expected total cost per unit of time are shown in a numerical example.