Transient behavior of single-server queueing processes with Erlang input

We say that {r*} is an Erlang process. The customers will be served by a single server in the order of their arrival. Suppose that the server is idle if and only if there is no customer waiting at the counter. Denote by x* the service time of the rath customer (n= 1, 2, ■ • • ). It is supposed that jx*} is a sequence of identically distributed, independent, positive random variables with distribution function