Pollaczek-Khinchine mean formula
= Pollaczek-Khinchine mean formula
{c}
For a stable $M/G/1$ queue with traffic intensity $\rho=\lambda\mathbb ES<1$, the mean waiting time before service is
$$
W_q=\frac{\lambda\mathbb ES^2}{2(1-\rho)}.
$$
Equivalently, the mean number in the system is
$$
L=\rho+\frac{\lambda^2\mathbb ES^2}{2(1-\rho)}.
$$