We introduce a simple approach for the analysis of the M/M/c queues with a
single class of customers and constant impatience time by finding simple Ma
rkov processes (see (2.1) and (2.15) below), and then by applying; this app
roach we analyze the M/M/1 queues with two classes of customers in which cl
ass 1 customers have impatience of constant duration, and class 2 customers
have no impatience and lower priority than class 1 customers.