A multi-server perishable inventory system with negative customer

In this paper, we consider a continuous review perishable inventory system with multi-server service facility. In such systems the demanded item is delivered to the customer only after performing some service, such as assembly of parts or installation, etc. Compared to many inventory models in which the inventory is depleted at the demand rate, however in this model, it is depleted, at the rate at which the service is completed. We assume that the arrivals of customers are according to a Markovian arrival process (MAP) and that the service time has exponential distribution. The ordering policy is based on (s, S) policy. The lead time is assumed to have exponential distribution. The customer who finds either all servers are busy or no item (excluding those in service) is in the stock, enters into an orbit of infinite size. These orbiting customers send requests at random time points for possible selection of their demands for service. The interval time between two successive request-time points is assumed to have exponential distribution. In addition to the regular customers, a second flow of negative customers following an independent MAP is also considered so that a negative customer will remove one of the customers from the orbit. The joint probability distribution of the number of busy servers, the inventory level and the number of customers in the orbit is obtained in the steady state. Various measures of stationary system performance are computed and the total expected cost per unit time is calculated. The results are illustrated numerically.     

Efficient Hierarchical Multi-Server Authentication Protocol for Mobile Cloud Computing

With the development of communication technologies, various mobile devices and different types of mobile services became available. The emergence of these services has brought great convenience to our lives. The multi-server architecture authentication protocols for mobile cloud computing were proposed to ensure the security and availability between mobile devices and mobile services. However, most of the protocols did not consider the case of hierarchical authentication. In the existing protocol, when a mobile user once registered at the registration center, he/she can successfully authenticate with all mobile service providers that are registered at the registration center, but real application scenarios are not like this. For some specific scenarios, some mobile service providers want to provide service only for particular users. For this reason, we propose a new hierarchical multi-server authentication protocol for mobile cloud computing. The proposed protocol ensures only particular types of users can successfully authenticate with certain types of mobile service providers. The proposed protocol reduces computing and communication costs by up to 42.6% and 54.2% compared to two superior protocols. The proposed protocol can also resist the attacks known so far.     

Improvement of the secure dynamic ID based remote user authentication scheme for multi-server environment

Recently, Liao and Wang proposed a secure dynamic ID based remote user authentication scheme for multi-server environment, and claimed that their scheme was intended to provide mutual authentication, two-factor security, replay attack, server spoofing attack, insider and stolen verifier attack, forward secrecy and user anonymity. In this paper, we show that Liao and Wang's scheme is still vulnerable to insider's attack, masquerade attack, server spoofing attack, registration center spoofing attack and is not reparable. Furthermore, it fails to provide mutual authentication. To remedy these flaws, this paper proposes an efficient improvement over Liao–Wang's scheme with more security. The computation cost, security, and efficiency of the improved scheme are well suited to the practical applications environment.     

A secure user anonymity-preserving biometric-based multi-server authenticated key agreement scheme using smart cards

Advancement in communication technology provides a scalable platform for various services, where a remote user can access the server from anywhere without moving from its place. It provides a unique opportunity for online services such that a user does not need to be physically present at the service center. These services adopt authentication and key agreement protocols in order to ensure authorized and secure access to the resources. Most of the authentication schemes proposed in the literature support a single-server environment, where the user has to register with each server. If a user wishes to access multiple application servers, he/she requires to register with each server. The multi-server authentication introduces a scalable platform such that a user can interact with any server using single registration. Recently, Chuang and Chen proposed an efficient multi-server authenticated key agreement scheme based on a user’s password and biometrics (Chuang and Chen, 2014). Their scheme is a lightweight, which requires the computation of only hash functions. In this paper, we first analyze Chuang and Chen’s scheme and then identify that their scheme does not resist stolen smart card attack which causes the user’s impersonation attack and server spoofing attack. We also show that their scheme fails to protect denial-of-service attack. We aim to propose an efficient improvement on Chuang and Chen’s scheme to overcome the weaknesses of their scheme, while also retaining the original merits of their scheme. Through the rigorous informal and formal security analysis, we show that our scheme is secure against various known attacks including the attacks found in Chuang and Chen’s scheme. Furthermore, we simulate our scheme for the formal security verification using the widely-accepted AVISPA (Automated Validation of Internet Security Protocols and Applications) tool and show that our scheme is secure against the replay and man-in-the-middle attacks. In addition, our scheme is comparable in terms of the communication and computational overheads with Chuang and Chen’s scheme and other related existing schemes.     

Analysis of a last come first served queueing system with customer abandonment

Motivated by manufacturing and service applications, we consider a single class multi-server queueing system working under the LCFS discipline of service. After entering the queue, a customer will wait a random length of time for service to begin. If service has not begun by this time she will abandon and be lost. For the GI/GI/s+M$\mathit{GI}/\mathit{GI}/s+M$ queue, we present some structural results to describe the relation between various performance measures and the scheduling policies. We next consider the LCFS M/M/s+M$M/M/s+M$ queue and focus on deriving new results for the virtual waiting time and the sojourn time in the queue (either before service or before abandonment). We provide an exact analysis using Laplace–Stieltjes transforms. We also conduct some numerical analysis to illustrate the impact of customer impatience and the discipline of service on performance.     

A finite source multi-server inventory system with service facility

In this article, we study a continuous review retrial inventory system with a finite source of customers and identical multiple servers in parallel. The customers arrive according a quasi-random process. The customers demand unit item and the demanded items are delivered after performing some service the duration of which is distributed as exponential. The ordering policy is according to (s, S) policy. The lead times for the orders are assumed to have independent and identical exponential distributions. The arriving customer who finds all servers are busy or all items are in service, joins an orbit. These orbiting customer competes for service by sending out signals at random times until she finds a free server and at least one item is not in the service. The inter-retrial times are exponentially distributed with parameter depending on the number of customers in the orbit. The joint probability distribution of the number of customer in the orbit, the number of busy servers and the inventory level is obtained in the steady state case. The Laplace–Stieltjes transform of the waiting time distribution and the moments of the waiting time distribution are calculated. Various measures of stationary system performance are computed and the total expected cost per unit time is calculated. The results are illustrated numerically.     

Traffic overflow in loss systems with selective trunk reservation

We consider two traffic streams competing for service at an n-server queuing system. Jobs from stream 1, the protected stream, are blocked only if all n servers are busy. Jobs from stream 2, the best effort stream, are blocked if n−r, r≥1, servers are busy. Blocked customers are diverted to a secondary group of c−n servers with, possibly, a different service rate. For the case r=1, we calculate the joint probabilities of the number of primary and secondary busy servers. For r>1, we describe a procedure for deriving the joint probabilities. These probabilities allow for the calculation of various performance measures including the overflow probabilities of the primary server and secondary server group. Our model is applicable to traffic control in communication networks that use the selective trunk reservation method.     

一个匿名的基于生物特征的多服务器的密钥认证协议方案的研究

随着通讯技术的快速发展,用户的口令与生物特征值的结合越来越普遍。最近,Chuang等提出了一个基于用户口令和生物特征值的匿名的多服务器的认证密钥协议方案。本文指出了Chuang等协议容易受到丢失智能卡攻击、伪装攻击、重放攻击和服务器伪装攻击,并且没有提供匿名性。因此针对上述协议的安全缺陷,本文提出了一个新的、有效的基于生物特征的多服务器的密钥认证协议。通过详细的安全和性能分析,证明出本文所提出的协议能够抵抗多种攻击,并且提供匿名性,与Chuang等协议相比,该新协议更加安全和实用。     

Sample-path analysis of queues with batch arrivals

In this article we give a deterministic sample path general relationship that relates workload and batch delays, and use it to extend the Pollaczek–Khintchine formula for a batch arrival single-server queueing model. We also give a conservation law for the same system with multiple classes that leads to new versions of conservation laws for Poisson batch arrival models. Our results are completely rigorous and hold under weaker assumptions than those given in the literature. We do not make stochastic assumptions, so the results hold almost surely on every sample path of the stochastic process that describes the system evolution. The article is self contained in that it gives a brief review of necessary background material.