| 1. |
- Enqvist, Per, et al.
(författare)
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A Marginal Allocation Approach to Resource Management for a System of Multiclass Multiserver Queues Using Abandonment and CVaR QoS Measures
- 2019
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Ingår i: 7th International Conference on Operations Research and Enterprise Systems, ICORES 2018. - Cham : Springer Verlag. ; , s. 119-133
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Konferensbidrag (refereegranskat)abstract
- A class of resource allocation problems is considered where some quality of service measure is set against the agent related costs. Three multiobjective minimization problems are posed, one for a system of Erlang-C queues and two for systems of Erlang-A queues. In the case of the Erlang-C systems we introduce a quality of service measure based on the Conditional Value-at-Risk with waiting time as the loss function. This is a risk coherent measure and is well established in the field of finance. An algebraic proof ensures that this quality of service measure is integer convex in the number of servers. In the case of the Erlang-A systems we introduce two different quality of service measures. The first is a weighted sum of fractions of abandoning customers and the second is Conditional Value-at-Risk, with the waiting time in queue for a customer conditioned on eventually receiving service. Finally, numerical experiments on the two system types with the given quality of service measures, are presented and the optimal solutions are compared.
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| 2. |
- Enqvist, Per, et al.
(författare)
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A state dependent chat system model
- 2019
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Ingår i: ICORES 2019 - Proceedings of the 8th International Conference on Operations Research and Enterprise Systems. - : SciTePress. ; , s. 121-132
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Konferensbidrag (refereegranskat)abstract
- The main purpose of this paper is to introduce a model of a chat based communication system, as well as developing the necessary tools to enable resource optimization with regards to a measure of the service quality. The system is modeled by a Markov process in continuous time and with a countable state space. The construction of the intensity matrix corresponding to this system is outlined and proofs of a stationary state distribution and an efficient way of calculating it are introduced. A numerical example for system optimization when the service measure is the average sojourn time is included as well as a heuristic algorithm for quicker solution generation.
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| 3. |
- Svensson, Göran, 1973-
(författare)
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Topics in Workforce Management in a Contact Center Context
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is written as a monograph covering topics in operations research and focusing on workforcemanagement in a contact center environment.This text is the result of a cooperative project between the Royal Institute of Technology (KTH) andTeleopti WFM.The main objective is to transform everyday problems faced at Teleopti into a mathematicalmodeling framework.The modeling aspect plays a prominent role and therefore, a large portion of this thesis deals withthe modeling aspects of contact center management.The majority of the models are proposed in terms of Markov queuing networks.The text is divided into five chapters.The first chapter covers the introduction and provides a short background ofthe basics of contact centers and workforce management.It also briefly mentions the necessary mathematical tools.In Chapter 2, a multiclass and multiserver queuing network with a common budget constraint is introduced.The multiobjective optimization problem of minimizing server costs while delivering a high quality of serviceis solved using the marginal allocation algorithm.The quality of service measures used to quantify customer satisfaction is the conditional value-at-riskmeasure and the fraction of abandoning customers.It is proved that the conditional value-at-risk measure is integer convex in terms of the number of serverswhen the customer waiting time is taken as the loss function.In Chapter 3, the contact center interagent fairness is considered.The importance of agent happiness in face of attrition is briefly discussed.To include the interagent fairness into the modeling procedure a multiclass and multiserver queuingnetwork is introduced.The servers are grouped into pools of exchangeable agents serving a subset of the customer classes.The interagent fairness measure can be introduced either as part of the objective function or as partof the optimization constraints.Robustness and multiperiod solutions are also considered.In Chapter 4, a limited state dependent server sharing system is considered in the context ofa chat based communication system.The proposed model is an extension of the Markov queuing model applied to telephone basedcommunication systems, where the agents may serve several customers concurrently.The service intensity provided depend on how many concurrent customers an agent serves whichincreases the complexity of the model.It is shown how agents of similar performance can be categorised together into groups and thus be handled separately.Several results pertaining to solving such a system are introduced and exemplified.In Chapter 5, the estimation of the parameters of the model presented in Chapter 4 is considered.This process is strongly data dependent, i.e., data driven, and a data classification system is proposedto the data available for the estimation.The chapter then proceeds toinvestigate frequentist and Bayesian strategies of parameterestimation under conditions of high and low resolution dataFurthermore, the model in Chapter 4 is evaluated in terms of a real chat center data set.
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| 4. |
- Enqvist, Per, et al.
(författare)
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Multi-server marginal allocation With CVaR and abandonment based QoS measures
- 2018
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Ingår i: ICORES 2018 - Proceedings of the 7th International Conference on Operations Research and Enterprise Systems. - : SciTePress. - 9789897582851 ; , s. 297-303
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Konferensbidrag (refereegranskat)abstract
- Two multi-objective minimization problems are posed, one for Erlang-C queues and one for Erlang-A queues. The objectives are to minimize the cost of added agents while also trying to optimize a quality of service measure. For the Erlang-C system we propose using the Conditional Value-at-Risk measure with waiting time as the loss function. We prove that this quality of service measure is integer convex in the number of servers. For the Erlang-A system we use the fraction of abandoning customers and some rate based weighting function as the service measure. Finally, a numerical comparison of the two system types is performed. The numerical results show the similarities between the two systems in terms of optimal points.
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| 5. |
- Enqvist, Per, et al.
(författare)
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Chat based contact center modeling system modeling, parameter estimation and missing data sampling
- 2017
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Ingår i: ICORES 2017 - Proceedings of the 6th International Conference on Operations Research and Enterprise Systems. - : SciTePress. - 9789897582189 ; , s. 464-469
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Konferensbidrag (refereegranskat)abstract
- A Markovian system model for a contact center chat function is considered and partially validated. A hypothesis test on real chat data shows that it is reasonable to model the arrival process as a Poisson process. The arrival rate can be estimated using Maximum likelihood. The service process is more involved and the estimation of the service rate depends on the number of simultaneous chats handled by an agent. The estimation is made more difficult by the low level of detail in the given data-sets. A missing data approach with Gibbs sampling is used to obtain estimates for the service rates. Finally, we try to capture the generalized behaviour of the service-process and propose to use generalized functions to describe it when little information is available about the system at hand.
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