Queuing theory had its beginning in 1909 with the research work of a danish engineer named a. k. erlang. in queuing problems, the number of arrivals per unit of time can be estimated by the . poisson refers to customers who refuse to join the waiting line because it is too long to suit their needs or interests. balking a queue is unlimited when its size is unrestricted, as in the case of a tollbooth serving automobiles jockeying occurs when customers switch between queues if they think they will get served faster by doing so.