Pollaczek-Khinchin (P-K)formula W:Average waiting time in queue AX2 W ,p=2= 21-p) Applying Little's Theorem N。=2W Number of customers in queue T=W+X Average system time:queueing delay service time Again Little's Theorem,we get the number of customers in system N=T=W+p=N。+P Weigiang Sun Communication Networks 3Weiqiang Sun Communication Networks Pollaczek-Khinchin (P-K) formula Applying Little’s Theorem 3 2 2(1 ) X W     X     ,   N W Q   T W X   Number of customers in queue W: Average waiting time in queue Average system time: queueing delay + service time Again Little’s Theorem, we get the number of customers in system N T W N          Q