𝒬 = QueueingProcess[λ,μ];

QueueProperties[𝒬 ,"QueueDiagram"]

L=QueueProperties[𝒬, "MeanSystemSize"]

W=QueueProperties[𝒬,"MeanSystemTime"]

L==λ W

𝒩 = QueueingNetworkProcess[(({{3.}, {0}, {0}})),(({{0, 1, 0}, {0, 0, 1}, {0, 0, 0}})),(({{4}, {7}, {8.2}})),(({{1}, {1}, {1}}))];

Probability[x==2&&y==1&&z==3,{x,y,z}\[Distributed]𝒩[∞]]

Probability[x==2&&y==1&&z==3,{x,y,z}\[Distributed]ProductDistribution[QueueingProcess[3,4][∞],QueueingProcess[3,7][∞],QueueingProcess[3,8.2][∞]]]

Probability[n == c, 
 Distributed[n, StationaryDistribution[QueueingProcess[λ, μ, c,c]]], 
      Assumptions->Element[c, Integers] && c > 0]

ErlangB[c,λ/μ]

FullSimplify[%-%%]