The basic process assumed by most of the queuing models is as follows. Customers who require a service are generated over time in an entry phase. These clients enter the queue management system and join a queue. At some point, a member of the queue is selected to provide the service, by some rule known as a service discipline. Then, the service required by the client is performed on a service mechanism, after which the client exits the queuing system. The following figure gives an outline of this process.