Consider Figure Q.2, in which there is an institutional network connected to the Internet. Suppose that the average obje

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Consider Figure Q.2, in which there is an institutional network
connected to the Internet.
Suppose that the average object size is 375,000 bits and that the
average request rate from
the institution’s browsers to the origin servers is 120 requests
per minute. Also suppose
that the amount of time it takes for the signal traveling from the
router on the Internet
side of the access link to the origin servers is two seconds on
average and it takes four
seconds for the signal coming back. Model the total average
response time as the sum of
the average access delay (that is, the delay from the Internet
router to the institution
router), and the average Internet delay, ignoring the delay in the
LAN. For the average
access delay, use T/(1−TB), where T is the average time required to
send an object over
the access link and B is the arrival rate of objects to the access
link. Note that the number
of significant digits after the decimal point should be limited to
four during the
calculation.

i. Find the average total response time. [8 marks]
ii. Now suppose a cache is installed in the institutional LAN.
Suppose that the miss rate
is 0.4. Find the total average response time. [8 marks]
iii. What is the total average response time if we upgrade the
access link with two parallel
links, one with 5 Mbps and another with 10 Mbps, instead of
installing a cache in the
institutional LAN? Assume that 30% of the traffic is distributed on
the 5 Mbps link
and the remaining 70% of the traffic is on the 10 Mbps link. [8
marks]