In the figure below, there is a local area network (LAN) with clients that are connected to the Internet through an access link. Suppose that the average object size is 850,000 bits and that the average request rate from the clients to the servers is 16 requests per second. In addition, assume that the amount of time it takes from when the router, R1, forwards an HTTP request until it receives the response is three seconds on average. Model the total average response time as the sum of the average access delay (the delay from R1 to R2) and the average Internet delay (the delay from R1 to the servers and back to R1). For the average access delay, use the formula delay = x/(1-xy), where x is the average time to send an object over the access link and y is the arrival rate of objects to the access link.

a) Find the total average response time.

b) Now suppose a cache is installed in the LAN. Suppose the miss rate is 0.4. Find the total response time.

Servers Internet Rl 15 Mbps Access Link R2 LAN Clients