![]() ![]() There are four types: single-channel/single-phase single-channel/multi-phase multi-channel/single-phase and multi-channel/multi-phase. This is referred to as the service rate: the capacity of the server in numbers of units per time period (i.e., 15 orders per hour).Īnother important aspect of the servicing system is the line structure. An important feature of the waiting structure is the time the customer spends with the server once the service has started. Others include a reservations first, treatment via triage (i.e., emergency rooms of hospitals), highest-profit customer first, largest orders first, “best” customers first and longest wait-time first. One of the most common used priority rules is “first come, first served” (FCFS). Queue discipline is the priority rule, or rules, for determining the order of service to customers in a waiting line. Factors to consider include the line length, number of lines and the queue discipline. The Servicing or Queuing System: The servicing or queuing system consists of the line(s) and the available number of servers. Variable – random arrival distributions, which is a much more common form of arrival.Ī good rule of thumb to remember the two distributions is that time between arrivals is exponentially distributed and the numbers of arrivals per unit of time is Poisson distributed.Constant – exactly the same time period between successive arrivals (i.e., machine controlled).The condition of the customer exiting the systemĪrrivals: Arrivals are divided into two types:.Queuing management consists of three major components: The point is that queues are within the control of the system management and design. Other common techniques include lowering prices on typically slow days to balance customer traffic throughout the week and establishing appointments with specific times for customers. For example, the simplest arrival-control mechanism is the posting of business hours. The store manager or business owner can exercise some control over arrivals. Figure 2: Number of Arrivals at FacilityĬustomers demand varying degrees of service, some of which can exceed normal capacity (Figure 3). The number of arrivals generally fluctuates over the course of the hours that the facility is available for business (Figure 2). ![]() At its most basic level, queuing theory involves arrivals at a facility (i.e., computer store, pharmacy, bank) and service requirements of that facility (i.e., technicians, pharmacists, tellers). Queuing theory, the mathematical study of waiting in lines, is a branch of operations research because the results often are used when making business decisions about the resources needed to provide service. Aquilano, Production and Operations Management, 1973, page 131. The optimal total cost is found at the intersection between the service capacity and waiting line curves. As service capacity increases, there is a reduction in the number of customers in the line and in their wait times, which decreases queuing cost. Initially, the cost of waiting in line is at a maximum when the organization is at minimal service capacity. The relationship between service capacity and queuing cost can be expressed graphically (Figure 1). Likewise, if customers are walking away disgusted because of insufficient customer support personnel, the business could compare the cost of hiring more staff to the value of increased revenues and maintaining customer loyalty. For example, if employees are spending their time manually entering data, a business manager or process improvement expert could compare the cost of investing in bar-code scanners against the benefits of increased productivity. The manager must weigh the added cost of providing more rapid service (i.e., more checkout counters, more production staff) against the inherent cost of waiting. The problem in virtually every queuing situation is a trade-off decision. Fortunately, Six Sigma professionals – through their knowledge of probability distributions, process mapping and basic process improvement techniques – can help organizations design and implement robust queuing models to create this competitive advantage. For this reason, businesses often utilize queuing theory as a competitive advantage. Queues are basic to both external (customer-facing) and internal business processes, which include staffing, scheduling and inventory levels. Understanding the nature of lines or “queues” and learning how to manage them is one of the most important areas in operations management. Given the intensity of competition today, a customer waiting too long in line is potentially a lost customer. Sometimes, it is a pleasant experience, but many times it can be extremely frustrating for both the customer and the store manager. Everyone has experienced waiting in line, whether at a fast-food restaurant, on the phone for technical help, at the doctor’s office or in the drive-through lane of a bank. ![]()
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