This equation computes the expected number of units in the system, L, for the case of a single server model (s = 1) with exponential service time, M = ∞∞
L = ρρ /( 1 - ρρ) = λλ/ (μ-λμ−λ) , where
ρρ = server utilization factor
μμ = mean service rate
λλ = mean arrival rate
This equation, Expected Units in the System (v3), s = 1, references 1 page