3. [Network Core, 10 pts] Suppose the capacity of output core link is 1 Mbps, and each user requires 200 kbps bandwidth when it is active. We have N = 10 users in total. 200 kb/s N users 1 Mbps link 200 kb/s a) If circuit-switching is used to deliver packets, how many users at most can transmit at the same time? Why? [5 pts] b) If packet-switching is used, assume each user is active only 10% of time (i.e., the probability of being active is p 10%). What is the probability that we have 9 users are active at the same time? [5 pts]