But the service rate is when the system is busy and 0 when the system is idle . The proportion of time the system is busy is . This is given the symbol, . The ratio is called the traffic intensity . When the server finishes a customer, the next one to be served is the one at the front of the queue.
Customers join at the back of the queue.
In this simple case, the service discipline does not effect the mean waiting time or the queue length. It does effect the distribution of waiting times for customers and hence the variance of waiting time. Service time has an exponential distribution, rate , mean . The system has 1 server. We look only at the steady state .