internet delay !

There is an institutional network connected to the internet by a 1 Mbps link. The institutional network is a very high-speed LAN (let 10 Mbps or more). Suppose that the average object size is 800,000 bits and that the average request rate from the institution's browsers to the original server is 1 request per second. 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 two second on average. Model the total average response time as the sum of the average access delay (that is the delay from Internet router to institution router), and the average internet delay, use d/(1-dR), where d is the average time required to send an object over the access link and R is the arrival rate of the objects to the access link.

a.Find the total average response time.
b.Now suppose a cache is installed is the institutional LAN. Suppose the hit rate is 0.5. Find the total response time.