Consider Figure $1,$ for which there is an institutional network connected to

the Internet. Suppose that the average object size is $100$k bits and that the average request rate from the institution$$s

browsers to the origin servers is $8$ requests 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 $2\mathrm{.}5$ seconds

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. For the average access delay, use $/(1\backslash$beta $),$

where $$ is the average time required to send an object over the access link and $\backslash$beta 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 institutional LAN. Suppose the miss rate is $0\mathrm{.}35.$ Find the total

response time. $($hint: The response time is approximately zero if the request is satisfied by the cache$)$

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CHAPTER $2$ APPLICATION LAYER

Origin servers

Public Internet

$15$ Mbps access link

$100$ Mbps LAN

Institutional network

Figure $2\mathrm{.}12$ Bottleneck between an institutional network and the Internet