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The purpose of this paper is to provide delay announcements for call centers with hyperexponential patience modeling. The paper aims to employ a state-dependent Markovian approximation for informing arriving customers about anticipated delay in a real call center.

Motivated by real call center data, the patience distribution is modeled by the hyperexponential distribution and is analyzed by its realistic significance, with and without delay information. Appropriate M/M/s/r+H₂ queueing model is structured, including a voice response system that is employed in practice, and a state-dependent Markovian approximation is applied for computing abandonment. Based on this approximation, a method is proposed for estimating virtual delays, and it is investigated about the problem of announcing virtual delays to customers upon their arrival.

There are two parts of findings from the results obtained from the case study and a numerical study of simulation comparisons. First, using an H₂ distribution for the abandonment distribution is driven by an empirical study which shows its good fit to real-life call center data. Second, simulation experiments indicate that the model and approximation are reasonable, and the state-dependent Markovian approximation works very well for call centers with larger pooling. It is concluded that our approach can be applied in a voice response system of real call centers.

Many results pertain to announcing delay information, customer reactions and links to estimating hyperexponential distribution based on real data that have not been established in previous studies; however, this paper analytically characterizes these performance measures for delay announcements.

The internet of things and just-in-time are the embryonic model of innovation for the state-of-the-art design of the service system. This paper aims to develop a fault-tolerant machining system with active and standby redundancy. The availability of the fault-tolerant redundant repairable system is a key concern in the successful deployment of the service system.

In this paper, the authors cogitate a fault-tolerant redundant repairable system of finite working units along with warm standby unit provisioning. Working unit and standby unit are susceptible to random failures, which interrupt the quality-of-service. The system is also prone to common cause failure, which tends its catastrophe. The instantaneous repair of failed unit guarantees the increase in the availability of the unit/system. The time-to-repair by the single service facility for the failed unit follows the arbitrary distribution. For increasing the practicability of the studied model, the authors have also incorporated real-time machining practices such as imperfect coverage of the failure of units, switching failure of standby unit, common cause failure, reboot delay, switch over delay, etc.

For deriving the explicit expression for steady-state probabilities of the system, the authors use a supplementary variable technique for which the only required input is the Laplace–Stieltjes transform (LST) of the repair time distribution.

For complex and multi-parameters distribution of repair time, derivation of performance measures is not possible. The authors prefer numerical simulation because of its importance in the application for real-time uses.

The stepwise recursive procedure, illustrative examples, and numerical results have been presented for the diverse category of repair time distribution: exponential (M), n-stage Erlang (Ern), deterministic (D), uniform (U(a,b)), n-stage generalized Erlang (GE_[n]) and hyperexponential (HE_[n]).

Concluding remarks and future scopes have also been included. The studied fault-tolerant redundant repairable system is suitable for reliability analysis of a computer system, communication system, manufacturing system, software reliability, service system, etc.

As per the survey in literature, no previous published paper is presented with so wide range of repair time distribution in the machine repair problem. This paper is valuable for system design for reliability analysis of the fault-tolerant redundant repairable.

The last decade has witnessed a growing concern among computer scientists to understand the complex interactions between humans and computer hardware. The work described in this paper is an experimental study of a user‐computer interaction on a time‐sharing computer terminal network over a period of 1 year. The user‐system interaction described in this paper refers to a university environment. The user‐system performance variables considered are arrival patterns of jobs, inter‐arrival time, connect time, cpu time and think time. The users of the systems are grouped into on‐ and off‐campus users; a two‐way analysis of variance without replications established that arrival volume depended upon the weekday but not upon the user group. The pattern of arrivals throughout one day required an empirical distribution. Coefficient of variation indicated hyper‐exponential distributions for inter‐arrival time, connect time and cpu time, but an exponential distribution for think time. Furthermore, the experimental research described in this paper supports the fact that a hypothesis to characterize the interaction between the user and the computing system can be developed for an efficient use of the system.

Telephone response system is the frontline of hospital operations. The purpose of this paper is to analyze a representative telephone response system of Veterans Affairs (VA) hospitals, address the existing inefficiency issues such as long call waiting time, and improve system resilience to changes.

Resource sharing schemes are proposed to improve the system performance in answering calls related to appointment booking and medication renewal. Discrete event simulation is adopted to model the current system and the resource sharing schemes.

The resource sharing schemes dramatically improve system performance reflected by the decrease of call waiting time and queue, as well as the extreme high utilization of agents in a key unit. Compared with the less desired alternative of hiring additional employees to mitigate the performance issues, the resource sharing schemes perform at par or even better. Sharing more resource during the peak hours can further balance the agent workload.

The resource sharing schemes could alleviate staffing shortage, long waiting time, and high-abandonment rate in the bottle-beck unit of the system, and lead to better utilization of scarce resources on the hospital floor. The concept reflects localized centralization efforts in traditionally highly decentralized telephone operations in hospital systems.

This research provides a structured approach to analyze the operations of a VA telephone response system. The developed simulation model is validated, and this provides a valuable tool for management to analyze the complicated telephone operations of the telephone systems of other VA and non-VA hospitals. Resource sharing constitutes a cost-effective solution for improving system performance and resilience.