For a queueing system we generally should define or know the following

• Inter arrival time(s) and its distributions, i.e., , which being important is assumed as i.i.d.

• The service time(s) (time to serve customer) and this has the probability distribution represented as .

• Storage capacity,  , and in general problems we consider  as  .

• Processing policy, e.g., First In First Out (FIFO), Last In First Out (LIFO), Random Order Processing, Priority Based Processing, etc.

We will first consider the G/G/m queueing system, where
G = Inter arrival time distribution is arbitrary
G = Service distribution is arbitrary
m = number of servers
Remember here the processing policy is also arbitrary