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queuethe build-up of customers who are delayed while waiting for service. Queuing can occur in a retail outlet where shoppers queue at supermarket checkouts or cars queue on petrol station forecourts. Similar queuing problems occur in factories where components queue to be processed on machines.
Variability in the demand for service and the variable time to complete service makes it difficult to judge the level of service to provide for customers. Where numerous service channels are provided, customers will experience few delays even when many customers arrive simultaneously for service. On the other hand, providing numerous service channels involves large labour costs, as in the case of supermarket checkout staff or bank clerks, or large investment in physical facilities, such as tanker berths or airport runways.
Queuing models employing statistical techniques can be used to analyse queues and to balance the cost of resources used to provide service against the cost of the time lost by customers while waiting for service.
These models consider the number of potential customers; the likely rate at which they arrive; whether they arrive singly or in batches; the number of parallel queues; maximum queue length; order of service (first come, first served or prioritized); number of servers; likely service time; and whether customers are served singly or in batches. For complex queues, SIMULATION techniques may be employed to decide the level of service to provide and how to organize the service facilities. See BALK, MULTIPLE CHANNEL-SINGLE PHASE.