Little’s Formula

General Single server Multi-server

q = lTq r = lTs r = lTs/N

w = lTw q = w + r u = rN

Tq = Tw + Ts q = w + Nr

q -- mean number of items in the system

• – utilization : fraction of busy time

u -- traffic intensity

w – mean number of items waiting to be served

l -- arrival rate

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