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The failure of computer software system is inevitable and it is important to analyze the performance of the system. It is equally important to consider the cost factor that occurs during repair. This paper models malware infected system and analyzes its behavior using a hybrid technique. A likelihood estimation is used for filtering malwares and improving the performance of the system. A discrete-time single server retrial queue with two types of arrivals is modeled to address infected system characteristics. A request which is originally legitimate known as the positive arrival, who finds the host free gets instant service; otherwise it joins the buffer. The malware (request) which is not detected by the filter known as the negative arrival will lead to the breakdown of the server, irrespective of the fact that the server is idle or busy. Further, it is assumed that suspicious request has no impact on the system when the server is under repair. Once the server is affected by suspicious request, it is sent for repair immediately. The retrial, service, and repair times are arbitrarily distributed. Performance characteristics such as mean buffer size, mean waiting time have been obtained. The reliability measures such as server availability, failure frequency, probability of packet lost, reliability of the underlying queueing system have also been derived. A cost model has been developed. The efficacy of filtering method and its level of accuracy have been demonstrated experimentally. The infected system has been detected from the performance measures and reliability metrics. A comparative study with and without filtering has been discussed numerically. The optimum cost analysis has also been presented. [ABSTRACT FROM AUTHOR]

Byline: M. Balasubramanian, R. Arumuganathan, A. Senthil Vadivu This paper analyses a non-Markovian bulk queueing model with the possibility of overloading and multiple vacations. It is considered that, on the completion of a service, if the queue length ξ is less than 'a', then the server leaves for a secondary job (vacation) of random length. On returning from this job, again if the queue length is still less than 'a', then the server repeats the secondary job until he finally finds, at least 'a' customers. After a service or a vacation completion epoch, if the server finds at least 'a' customers waiting for service, say ξ (a≤ξ

Byline: M. Senthil Kumar, R. Arumuganathan This paper analyses a single server batch arrival retrial queue with active breakdowns, two types of repair and second optional service (SOS). The server provides preliminary first essential service (FES) to the primary arriving customers or customers from retrial group. The server is subject to breakdowns. The customer under service during the failure decides, with probability q, to join the orbit (impatient customer) and, with complementary probability 'p', to remain in the server for repair in order to conclude his remaining service (patient customer). It is considered that the repair time of server during the presence of patient customer and the repair time of the server while the customer (impatient customer) joining the orbit due to failure are different. On completion of FES successfully, the customer may opt for SOS with probability α. Reliability of the proposed model is analysed. Some particular cases are also discussed. Other performance measures are also obtained. The effects of several parameters on the system are analysed numerically.

Byline: S. Jeyakumar, R. Arumuganathan This paper deals with a single server Poisson queue with state dependent service. The service is rendered with different service modes as singly or in bulk according to the queue length. The service starts only if at least one customer is waiting for service. The server switches over from single service to bulk service only at service initiation epoch according to the queue length. If the number of customers waiting for service is ξ (1 ≤ ξ < a), then the server serves one by one. At the service initiation epoch, if the number of waiting customers ξ is at least 'a' (a < b), then the service is rendered according to Neut's general bulk service rule. At the service completion epoch, if there are no customers in the queue, the server avails multiple vacations, until he finds at least one customer in the queue. The Probability Generating Function (PGF) of the queue size and performance measures are obtained. Numerical results are presented in order to illustrate the effectiveness of performance of the state dependent queue.

This paper analysis a discrete time infinite capacity queueing system with correlated arrival and negative customers served by two state Markovian server. Positive customers are generated according to the first order Markovian arrival process with geometrically distributed lengths of On periods and Off periods. Further, the geometrically distributed arrival of negative customer removes the positive customers is any, and has no effect when the system is empty. The server state is a two state Markov chain which alternate between Good and Bad states with geometrically distributed service times. Closed-form expressions for mean queue length, unfinished work and sojourn time distributions are obtained. Numerical illustrations are also presented. [ABSTRACT FROM AUTHOR]

In this paper, a batch arrival single server retrial queue with modified vacations under N-policy is considered. If an arriving batch of customers finds the server busy or on vacation, then the entire batch joins the orbit in order to seek the service again. Otherwise, one customer from the arriving batch receives the service, while the rest joins the orbit. The customers in the orbit will try for service one by one when the server is idle with a classical retrial policy with the retrial rate 'jv', where 'j' is the size of the orbit. At a service completion epoch, if the number of customers in the orbit is zero, then the server leaves for a secondary job (vacation) of random length. At a vacation completion epoch, if the orbit size is at least N, then the server remains in the system to render service for the primary customers or orbital customers. On the other hand, if the number of customers in the orbit is less than 'N' at a vacation completion epoch, the server avails multiple vacations subject to maximum 'M' repeated vacations. After availing 'M' consecutive vacations, the server returns to the system to render service irrespective of the orbit size. The model is studied using supplementary variable technique. For the proposed queueing system, the probability generating function of the steady state queue size distribution at an arbitrary time is obtained. Various performance measures are derived. A cost model for the queueing system is developed. Numerical illustration is provided. [ABSTRACT FROM AUTHOR]

This paper describes an unreliable server batch arrival retrial queue with two types of repair and second optional service. The server provides preliminary first essential service (FES) to the primary arriving customers or customers from retrial group. On successful completion of FES, the customer may opt for second optional service (SOS) with probability α. The server is subject to active break downs. The customer under FES (or SOS) during the failure decides, with probability q, to join the orbit(impatientcustomer) and, with complementary probability p, to remain in the server for repair in order to conclude his remaining service (patientcustomer). Both service and repair times are assumed to have general distribution. It is considered that the repair time of server during the presence of patient customer and the repair time of the server while the customer (impatientcustomer) joining the orbit due to failure, are different. For this queueing system, the orbit and system size distributions are obtained. Reliability of the proposed model is analysed. Some particular cases are also discussed. Other performance measures are also obtained. The effects of several parameters on the system are analysed numerically. [ABSTRACT FROM PUBLISHER]