Transient distribution of an M-M-infinity queue (source code)

= Transient distribution of an M-M-infinity queue

If $X_0=n$ and $p_t=e^{-\mu t}$, then
$$
X_t\overset{d}{=}
\operatorname{Binomial}(n,p_t)
+\operatorname{Poisson}\!\left(\frac\lambda\mu(1-p_t)\right),
$$
with independent summands. The binomial term counts surviving initial customers; <Poisson thinning> gives the surviving later arrivals.