A convenient notation to denote queueing system is as follows :

a/b/c : d/e/f

where

a = Arrivals' distribution

b = Service time distribution

c = Number of servers or channels

d = Service discipline

e = System capacity

f = Calling population.

In the above, a and b usually take one of the following distribution with its symbol :

M = Exponential distribution for inter-arrival or service time and Poisson arrival.

E_{k} = Erlangian or gamma distribution with parameter k.

D = Constant or deterministic inter-arrival or service time.

G = General distribution (of service time)

Generally f is taken as ∞ (infinity) and it is omitted while representing a queue.