A queuing system is described by calling population, Arrival rate, Service, mechanism, System capacity, Queuing discipline.
Many other more complex queuing models that typically change the customer's position in the queue according the time spend in the queue, expected service duration and/or priority. These methods are generally for computer multi-access systems.
Closed -queuing systems, which are identified by a closed loop in which the jobs move through the queuing net. The number of jobs are fixed for the whole simulation time.
A typical example of a closed queuing system is a multi user system with n terminals and single central processing unit.
The jobs circle between the terminals and the cpu; their number stays constant all over the simulation time.
More ever it has to be decided whether:
It is possible to leave the queue without being served at all.
The number of jobs in the queue is limited.
There are priorities for the jobs.
It is possible for a job with high priority to interrupt the service for a low priority one and to occupy the service station immediately when entering the queue.