m One Paper 0688436 Computer Conmmunlcations Problems 1-3 (30 marks) Suppose 10 users share a 1 Mbps link. Also suppose each user requires 500 kbps when transmitting, but each user transmits only 20 percent of the time. Find the probability that there are at most two users transmitting simultaneously at any given time. (40 marks) Consider Figure 2 for which there is an institutional network connected to the Internet. Suppose that the average object size is 120,000 bits and the traffic intensity on the access link is -0.8. Also suppose that the amount of time it takes from when the router on the Internet side of the access link forwards an HTTP request until it receives the response is 2.4 seconds on average. Let the average response time be the sum of the average access delay and the average Internet delay publie 15 Mps access Iink 2 Daps Figure 2: Diagram for Problem 3 i). Find the total average response time. i). Now suppose a cache is installed in the institutional LAN. Suppose the miss rate is 0.3. Find the total response time. Note that the respouse time is close to zero if the request is satisfied by the cache. 2/3