“…[15,19], in the case of ϕ r (n) = min(r/n, 1), n ∈ N, an r-server PS system, where all requests are served in a PS mode, but each request receives at most the capacity of one processor, cf. [8, p. 283], [3,4,9], in case of ϕ r,k (n) = min(r/(n + k), 1), n ∈ N, an r-server PS system with k ∈ N permanent requests, in the case of ϕ ∞ (n) = 1, n ∈ N, an infinite-server system.…”