Proof of P-K formula(Cont. Customer i starts to receive service Customer i arrives W X Xi-1 Xi-2 Xi-3 Xi-4 W=R+∑X, R N,3 EW,]=E[R]+E[X]E[N,]=R+X·N。 W=R+X·No By Little's Theorem,No =2.W W=R/-p).P=-X Weigiang Sun Communication Networks 6Weiqiang Sun Communication Networks Proof of P-K formula (Cont.) 6 Xi Xi-1 Xi-2 Xi-3 Xi-4 Customer i starts to receive service Customer i arrives Wi Ri Ni =3 1 i i i i j W R X j i N      [ ] [ ] [ ] [ ] E W E R E X E N R X N i i i Q      By Little’s Theorem, N W Q    W R X N    Q W R   /(1 )  X     ,  