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2019, Unpublished
Performance Modelling to predict the quality of service (QoS) of computer systems and networks is widely applied. Similarly there is an abundant literature on the analysis and optimisation of supply chains and inventory control. This paper addresses some problems at the interface between these two areas, since computer systems and networks are widely used to control supply chains and E-Commerce systems. We develop an analytical modelling approach using queueing theory to study the impact of cyber-attacks on the economic performance of warehouse that sells perishable goods such as food that has a limited shelf life. We derive expressions to predict the loss of income that results from cyber-attacks on a web site used to order goods, and illustrate them with numerical examples.
Electronic Notes in Theoretical Computer Science, 2020
In this paper we present two performance models of a web-based sales system, one without the presence of an attack and the other with the presence of a denial of service attack. Models are formulated using the PEPA formalism. The PEPA eclipse plug-in is used to support the creation of the PEPA models for the web-based sales system and the automatic calculation of the performance measures identified to evaluate the models. The evaluation of the models illustrates how the performance of the warehouse's sale is negatively affected by denial of service attack through preventing some or all customers' orders from being fulfilled. The resultant delay on selling perishable products would result on products being discarded.
Besides other relevant components encompassing the dependability aspects of contemporary e-Commerce systems (reliability, maintainability, safety, security, etc.), availability has always been considered the most prominent one, having minded its direct impact on Internet companies' reputation and financial revenues. Being a synonym for a characteristic of a resource/system that is committable, operable, or usable upon demand to perform its designated or required function, availability is the single crucial attribute of each e-Commerce system and a basic prerequisite that makes the huge difference between success and failure. In order to assure and maintain pertinent Quality-of-Service (QoS) levels of Web services being delivered online, including high availability, stochastic predictive models have to be developed and evaluated on a regular basis. The aim of the paper is to address the most significant aspects of stochastic modeling of e-Commerce systems' availability, using the class of Generalized Stochastic Petri Nets (GSPNs), as well as Continuous-Time Markov Chains (CTMCs), a class of stochastic processes underlying GSPNs. A few basic e-Commerce system configurations have been modeled and analyzed in the case of a corrective maintenance. The current possible analysis methodologies that address the concept of availability have been discussed, and adequate software tools have been reviewed, as well.
In the present scenario of competitiveness, enhancement efforts and the adoption of new technologies is crucial for a company to reach high levels of effectiveness. Online retailing is one such strategy and it is continuing to expand quickly. As Information Technology progresses rapidly, consumers can access the internet more convenient and thus they are more interested in online shopping. Retailers who have effectively used the internet to manage their business operations have been able to discover new ways to handle their inventories and save costs. With powerful inventory control and order management features firms can increase sales and fulfil orders economically. Internet retailers must optimize inventory replenishment decisions to enhance their profits. This paper develops an innovative mathematical model for E-tailing inventory system and provides the optimal values in order to maximize the benefits. A numerical example is provided to illustrate the proposed E-tailing model.
Modelling, Identification and Control, 2017
This paper we propose a continuous review inventory system for perishable inventory with lost sales. We consider a single demand types and a single unit for placing and depleting the demand. The demand, lead time and life time is random variables according to an exponentially distributed. We develop the inventory system as a Markov process with impatient customer. We formulate the model as a M/M/∞ queuing model given a (r, S) and (r, K) policies. The state of system is a number of on-hand inventories and obtains the limited steady state probability at state n. The limited steady state probability approach is based on a basic rule of the rate of transition out equal to the rate of transition into the state. Numerical results indicate that the model provides no difference of the limited steady state probability comparing to the results of the augmented generator matrix. Furthermore, the results show that the (r, S) policy provides more efficiency than the (r, K) policy as (K > r) on the probability of lost sale (P0) whereas the (r, S) policy provides a larger on-hand inventory than the (r, K) policy as (K > r).
13th IEEE International Workshops on Enabling Technologies: Infrastructure for Collaborative Enterprises, 2004
Companies that rely on the Internet for their daily business are challenged by uncontrolled massive worm spreading and the lurking threat of large-scale distributed denial of service attacks. We present a new model and methodology, which allows a company to qualitatively and quantitatively estimate possible financial losses due to partial or complete interruption of Internet connectivity. Our systems engineering approach is based on an in-depth analysis of the Internet dependence of different types of enterprises and on interviews with Swiss telcos, backbone and Internet service providers. A discussion of sample scenarios illustrates the flexibility and applicability of our model.
International Research Journal of Business Studies, 2021
Coronavirus disease (Covid-19) is an infectious disease caused by a newly found coronavirus. Coronavirus 2(SARS-CoV-2), caused an illness known as Covid-19, which was similar to SARS and was characterized usually by fever and breathing symptoms. World Health Organization in March 2020 declared Covid-19 as pandemic. Social distancing is the only measure in the absence of any vaccine to reduce the spread of this virus so many countries including India are going under lockdown. In the lockdown, the Government ordered closure of all the brick-and-mortar businesses. In this time of crises customers have only choice to purchase essential products from e-commerce portals. Prime Minister Narendra Modi announced that essential items could be purchased through e-commerce portals, all e-commerce businesses were instructed by the Ministry of Consumer Affairs to take proper precautions and hygiene in their entire supply chain process. This paper suggests a model to incorporate hygiene in reverse...
We discuss two queueing-inventory systems with catastrophes in the warehouse. Catastrophes occur according to Poisson process and upon arrival of a catastrophe all inventory in the system is instantly destroyed. But consumer customers in the system (in the server or in the buffer) continue still waiting for the replenishment of the stock. The arrivals of the consumer customers follow a Markovian Arrival Process (MAP) and they can be queued in an infinite buffer. Service time of a consumer customer follows a phase-type distribution. The system receives negative customers whose have Poisson flows to service facility and upon arrival of a negative customer one consumer customer is pushed out from the system, if any. One of two replenishment policies can be used in the system: either (s,S) or (s,Q). If upon arrival of the consumer customer, the inventory level is zero, then according to the Bernoulli scheme, this customer is either lost (lost sale scheme) or join the queue (backorder sa...
example, an unexpected increase in demand at a facility would probably cause a stock-out at that facility and may affect other facilities in the system. One way to mitigate the impact of a demandinduced disruption is the ability to react immediately, which could be achieved by using real-time information. However, in distribution systems, it is difficult for the decision maker to update inventory target parameters when such disruptions are observed, because in the short term those changes could be attributed to deviation in normal consumption patterns.
Proceedings 2002 IEEE International Conference on Robotics and Automation (Cat. No.02CH37292)
Procurement, i.e., the process of obtaining materials or services and managing their inflow into organizations, is a critical process in supply chain management. Internet technologies offer attractive opportunities to reduce purchasing costs while increasing the speed and efficiency of the procurement process through seamless network integration and automated execution of key tasks. This paper attempts to model e-procurement from a lead time perspective, to capture the effects of Internet technologies on the procurement lead time. The model we develop is a multiclass queueing network called a probabilistic reentrant line. The model captures several important facets of an eprocurement process, such as use of electronic RFQ (request for quotation) in systematic sourcing, use of Internet auctions in spot purchasing, contention for procurement resources, randomness in execution times of procurement tasks, and concurrent execution of multiple procurement activities. The analysis of the queueing model suggests that end-to-end lead times in eprocurement can be compressed in ingenious ways using standard queueing theoretic techniques.
2010
Satisfying customers by delivering demands at agreed time, with competitive prices, and in satisfactory quality level are crucial requirements for supply chain survival. Incident of risks in supply chain often causes sudden disruptions in the processes and consequently leads to customers losing their trust in a company's competence. Rush orders are considered to be one of the main types of supply chain risks due to their negative impact on the overall performance. Using integrated definition modeling approaches (i.e. IDEF0 & IDEF3) and simulation modeling technique , a comprehensive integrated model has been developed to assess rush order risks and examine two risk mitigation strategies. Detailed functions sequence and objects flow were conceptually modeled to reflect on macro and micro levels of the studied supply chain. Discrete event simulation models were then developed to assess and investigate the mitigation strategies of rush order risks, the objective of this is to minimize order cycle time and cost.
Journal of Applied Mathematics and Stochastic Analysis, 2007
We analyze and compare three (s,S) inventory systems with positive service time and retrial of customers. In all of these systems, arrivals of customers form a Poisson process and service times are exponentially distributed. When the inventory level depletes to s due to services, an order of replenishment is placed. The lead-time follows an exponential distribution. In model I, an arriving customer, finding the inventory dry or server busy, proceeds to an orbit with probability γ and is lost forever with probability (1−γ). A retrial customer in the orbit, finding the inventory dry or server busy, returns to the orbit with probability δ and is lost forever with probability (1−δ). In addition to the description in model I, we provide a buffer of varying (finite) capacity equal to the current inventory level for model II and another having capacity equal to the maximum inventory level S for model III. In models II and III, an arriving customer, finding the buffer full, proceeds to an o...
2018
The three-dimensional Perishable Queuing-Inventory System (PQIS) models with positive service time and delayed feedback are studied in this paper. We assume that the customers either leave the system with/without purchasing an item or join the orbit for the decision making. We apply the (s, S) replenishment policy with the positive order lead time. The approximate formulas are developed to calculate the joint distributions and performance measures of the system. The high accuracy of the approximate formulas is confirmed by the numerical experiments.
2000
This article considers a continuous review perishable (s,S) inventory system in which the demands arrive according to a Markovian arrival process (MAP). The lifetime of items in the stock and the lead time of reorder are assumed to be independently distributed as exponential. Demands that occur during the stock-out periods either enter a pool which has capacity N(< ∞) or are lost. Any demand that takes place when the pool is full and the inventory level is zero is assumed to be lost. The demands in the pool are selected one by one, if the replenished stock is above s, with time interval between any two successive selections distributed as exponential with parameter depending on the number of customers in the pool. The waiting demands in the pool independently may renege the system after an exponentially distributed amount of time. In addition to the regular demands, a second flow of negative demands following MAP is also considered which will remove one of the demands waiting in the pool. The joint probability distribution of the number of customers in the pool and the inventory level is obtained in the steady state case. The measures of system performance in the steady state are calculated and the total expected cost per unit time is also considered. The results are illustrated numerically.
International Journal of Information …, 2009
This paper presents a probabilistic security model for supply chain management systems (SCM) in which the basic goals of security (including confidentiality, integrity, availability and accountability, CIAA) are modeled and analyzed. Consequently, the weak points in system security are identified. A stochastic model using measurable values to describe the information system security of a SCM is introduced. Information security is a crucial and integral part of the network of supply chains. Each chain or driver requires a different security level according to the services it contributes to the overall SCM system. Different probabilistic weights are assigned to the four goals CIAA of security depending on the SCM driver's mission. A Semi-Markov chain model is used to describe the probabilistic nature of different security levels for each driver in the system. A comparison of the steady-state security for a multi-driver model with different levels of attack is performed, and the results analyzed. Enhanced supply chain security could be achieved by identifying the effects of attacks on the security goals of an organization. The use of this model helps to identify weak points in supply chain system security, and offers hints on how to strengthen them. The model is tested by considering intrusion scenarios representing different levels of attack on the SCM system. An analysis of the results is performed using an interactive application. [Article copies are available for purchase from InfoSci-on-Demand.com]
Decision Sciences, 2007
In this article we explore the profitability of different operations models used by online grocers and develop a linear demand model in a competitive setting to better understand the trade-offs made by two competing online grocers in choices for distribution strategy (leverage or direct) and product focus (perishable or nonperishable). We find that the results derived in the duopoly setting are different from those in a monopolistic setting. Specifically, we determine that there is a threshold value for the secondary competitive effects in the demand function that determines how the prices and profitability of an online grocer will be affected by the supply chain length of its competitor. There is also a threshold value for the ratio of supply chain lengths of the two competitors that determines whether product perishability increases or decreases profits. We demonstrate that the existence of this threshold is robust when considering capacity constraints. Further, we show, assuming that supply chain length can be optimized, how the relative size of the infrastructure change cost (when compared with that of the competitor) coupled with the perishability of the product determines the profitability of an investment leading to a shorter supply chain.
Operations Research, 2008
We consider a perishable inventory system with Poisson demands, fixed shelf lives, constant lead times, and lost sales in the presence of nonnegligible fixed ordering costs. The inventory control policy employed is the continuous-review (Q r) policy, where r < Q. The system is modeled using an embedded Markov process approach by introducing the concept of the effective shelf life of a batch in use. Using the stationary distribution of the effective shelf life, we obtain the expressions for the operating characteristics and construct the expected cost rate function for the inventory system. Our numerical study indicates that the determination of the policy parameters exactly as modeled herein results in significant improvements in cost rates with respect to a previously proposed heuristic. We also compare the (Q r) policy with respect to a time-based benchmark policy and find that the (Q r) policy might be impractical for rare events, but overall appears to be a good heuristic policy.
Mathematics
In this paper, we studied single-server models of queuing-inventory systems (QIS) with catastrophes in the warehouse part and negative customers (n-customers) in service facility. Consumer customers (c-customers) that arrived to buy inventory can be queued in an infinite buffer. Under catastrophes, all inventory of the system is destroyed but customers in the system (on server or in buffer) are still waiting for replenishment of stocks. Upon arrival of n-customer one c-customer is pushed out, if any. One of two replenishment policies (RP) can be used in the system: either (s,S) or randomized. In the investigated QISs, a hybrid service scheme was used: if upon arrival of the c-customer, the inventory level is zero, then according to the Bernoulli scheme, this customer is either lost (lost sale scheme) or joining the queue (backorder scheme). Mathematical models of the investigated QISs were constructed as two-dimensional Markov chains (2D MC). Ergodicity conditions of the investigate...
IJARCSSE, 2018
Opening a new supermarket is a task especially when there is no other supermarket to make a comparison with. Decision on the number of tills or point-of-sale (POS) terminals to use becomes an issue. The consequences of not getting the number of tills right could lead to wastage due to too many POS terminals acquired that are not needed, and shoppers reluctance to patronize the supermarket due to an incessant queue caused by too few POS availability. This paper objective is to model hypothetically the supermarket queue in such a way that the aforementioned problems being experienced are reduced if not removed. Formulated data were used for the model on spreadsheet. The automation of the model is left for future work.
Information & Security: An International Journal, 2013
The same Information and Communication Technologies (ICT) that have contributed tremendously to the productivity of supply chain companies and governments alike, as well as to the global competitiveness of the European Union, expose modern societies to a range of cyber threats. ICT systems are fundamental to ensure that undisrupted flows of merchandise and critical supplies, such as oil, minerals, rare earths, pharmaceuticals and food are moved in and out of the EU territory. Past events have revealed the vulnerability of global supply chains to crime and terrorism. However, previous research does not highlight how these threats may be affected with the support of cyber attacks. Hence, by means of a literature review and experts' validation, this study develops a set of three scenarios that outline how cybercrime could jeopardize security of supply chains and, consequently, the wellbeing of European citizens. Finally, implications for managers and EU agencies are discussed.
Technology Innovation Management Review
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