Sharif Digital Repository

Optimal queuing system design includes deciding about some variables such as location, capacity, price, and delivery time. In order to develop an optimized system, it is essential to solve the optimization problem for all the decision variables simultaneously. In this paper, a make-to-order system is considered. In this system, some facilities are developed in different points. According to the make-to-order system definition, these facilities keep no inventory from final product. Orders are received from customers and the requested products are assembled. Due to existence of some differences among customers, they are divided into two distinct categories including express and regular... 

This research has modelled a queuing system with no standard states. In order to analyse these systems, some parameters such as the mean of waiting time and the length of queue are computed. These situations usually occur when there is delay in the service, for example, in the gas queuing system that cars are unable to leave after receiving the required services due to the presence of other cars in front of them. These kinds of non-standard queuing systems are usually applied to the assembly and production lines. In this paper, a queuing model for the special non-standard state queuing system is developed to be used in gas stations. The proposed model is implemented in fuel stations in Iran... 

A new multi-objective intermodal hub-location-allocation problem is modeled in this paper in which both the origin and the destination hub facilities are modeled as an M/M/m queuing system. The problem is being formulated as a constrained bi-objective optimization model to minimize the total costs as well as minimizing the total system time. A small-size problem is solved on the GAMS software to validate the accuracy of the proposed model. As the problem becomes strictly NP-hard, an MOIWO algorithm with an efficient chromosome structure and a fuzzy dominance method is proposed to solve large-scale problems. Since there is no benchmark available in the literature, an NSGA-II and an NRGA are... 

A new multi-objective intermodal hub-location-allocation problem is modeled in this paper in which both the origin and the destination hub facilities are modeled as an M/M/m queuing system. The problem is being formulated as a constrained bi-objective optimization model to minimize the total costs as well as minimizing the total system time. A small-size problem is solved on the GAMS software to validate the accuracy of the proposed model. As the problem becomes strictly NP-hard, an MOIWO algorithm with an efficient chromosome structure and a fuzzy dominance method is proposed to solve large-scale problems. Since there is no benchmark available in the literature, an NSGA-II and an NRGA are... 

K-ary n-cubes have been one of the most popular interconnection networks for practical multicomputers due to their ease of implementation and ability to exploit communication locality found in many parallel applications. This paper describes an analytical model for k-ary n-cubes with dimension-ordered routing. The main feature of the model is its ability to captures network performance when an arbitrary number of virtual channels are used to reduce message blocking. Simulation experiments reveal that the latency results predicted by the analytical model are in good agreement with those provided by the simulation model. © 2002 Elsevier Science B.V. All rights reserved  

In this paper, a novel multi-objective location model within multi-server queuing framework is proposed, in which facilities behave as M/M/m queues. In the developed model of the problem, the constraints of selecting the nearest-facility along with the service level restriction are considered to bring the model closer to reality. Three objective functions are also considered including minimizing (I) sum of the aggregate travel and waiting times, (II) maximum idle time of all facilities, and (III) the budget required to cover the costs of establishing the selected facilities plus server staffing costs. Since the developed model of the problem is of an NP-hard type and inexact solutions are... 

Large Multi-Processor Systems-on-Chip use Networks-on-Chip with a high degree of reusability and scalability for message communication. Therefore, network infrastructure is a crucial element affecting the overall system performance. On the other hand, technology improvements may lead to much energy consumption in micro-routers of an on-chip network. This necessitates an exhaustive analysis of NoCs for future designs. This paper presents a comprehensive analytical model to predict message latency for different data flows traversing across the network. This model considers channel buffers of multiple flits which were not previously studied in NoC context. Also, architectural descriptions of... 

Although several analytical models have been proposed for wireless sensor networks (WSNs) with different capabilities, very few of them consider the effect of general service distribution as well as design constraints on network performance. This paper presents a new analytical model to compute message latency in a WSN with loop-free Bellman Ford routing strategy. The model considers limited buffer size for each node using M/G/1/k queuing system. Also, contention probability and resource utilization are suitably modeled. The results obtained from simulation experiments confirm that the model exhibits a high degree of accuracy for various network configurations. © 2009 IEEE  

In this paper, we introduce an efficient route discovery mechanism to enhance the performance and multicast efficiency of On-Demand Multicast Routing Protocol (ODMRP). Our framework, called limited flooding ODMRP, improves multicasting mechanism by efficiently managing flooding mechanism based on delay characteristics of the contributing nodes. In our model, only the nodes that satisfy the delay requirements can flood the Join-Query messages. We model the contributing nodes as M/M/1 queuing systems. Our framework considers the significant parameters in delay analysis, including random packet arrival, service process, and random channel access in the relying nodes, and exhibits its best... 

In this paper, we consider a broadband secondary transmitter-receiver pair which interferes with N narrowband primary users and study the effect of cognition and cooperation on the maximum stable throughput. In our study we focus on four transmission protocols as well as two channel types, i.e., flat fading and frequency selective fading. In the cooperative protocols, the broadband transmitter relays the packets of the primary users which have not correctly decoded at the primary receiver. The analysis includes random packet arrivals at the transmitters which may impact on the maximum stable throughput. Moreover, sensing errors at the secondary user are considered. In this paper, we derive... 

This study is dedicated to order penetration point (OPP) strategic decision making which is the boundary between make-to-order (MTO) and make-to-stock (MTS) policies. A multiproduct multiechelon production supply chain is considered where the first production stage manufactures semifinished products based on an MTS policy to supply the second production stage which operates on the MTO policy. The producer desires to find the optimal fraction of processing time fulfilled by supplier and optimal semifinished products buffer capacity in OPP. To calculate system performance indexes, the matrix geometric method is employed. Afterward, optimal solutions are obtained by enumeration and direct... 

A novel bi-objective multi-server location-allocation (LA) model is developed in this paper, in which the facilities are modeled as an M/M/m queuing system. Further, capacity and budget limitations are provided to make the LA problem more realistic. The two objective functions include (1) minimizing aggregate waiting times and (2) minimizing the maximum idle time of all facilities. Since the proposed model is NP-hard, a meta-heuristic algorithm called multi-objective harmony search algorithm (MOHA) is developed to solve it. In this algorithm, a new presentation scheme that satisfies most of the model constraints is proposed. Since there is no benchmark available in the literature to validate... 

In this paper, we introduce an efficient route discovery mechanism to enhance the performance and multicast efficiency of On-Demand Multicast Routing Protocol (ODMRP). Our framework, called limited flooding ODMRP, improves multicasting mechanism by efficiently managing flooding mechanism based on delay characteristics of the contributing nodes. In our model, only the nodes that satisfy the delay requirements can flood the Join-Query messages. We model the contributing nodes as M/M/1 queuing systems. Our framework considers the significant parameters in delay analysis, including random packet arrival, service process, and random channel access in the relying nodes, and exhibits its best... 

Many performance evaluations for the IEEE 802.11 Distributed Coordination Function (DCF) have been previously reported in the literature; most studies are based on saturation analysis, and a few models under a finite-load condition adopt an M/G/1 queuing system. However, using M/G/1 queuing only considers the first moment of the frame service time to derive the probability of the transmission queue being vacant. In this paper, we model the DCF using the parallel space-time Markov chain, where the frame arrivals are tracked by monitoring the transmission queue during transitions between successive states of the space-time Markov chain. The proposed framework provides the possibility of... 

Speed and price are the two most important factors in customer satisfaction and business success in today's competitive environment. Time-based product differentiation and segment pricing have provided firms with a great opportunity to profit enhancement. This paper presents a coding system for pricing/queuing models in the literature. In this article, a service/make-to-order firm with heterogeneous price and delivery time-sensitive customers as an M/M/1 queuing system is analyzed. The firm uses customers' heterogeneity to create market segments. Products offered to each segment differ only in price and delivery time. The objective of this profit-maximizing firm is to determine optimal... 

A novel bi-objective three-echelon supply chain problem is formulated in this paper in which cross-dock facilities to transport the products are modeled as an M/M/m queuing system. The proposed model is validated using the epsilon constraint method when applied to solve some small-size problems. Since the problem belongs to the class of NP-hard and that it is of a bi-objective type, a multi-objective particle swarm optimization (MOPSO) algorithm with a new solution structure that satisfies all of the constraints is developed to find Pareto solutions. As there is no benchmark available in literature, three other multi-objective meta-heuristic algorithms called non-dominated ranking genetic...