EECS325 Homework Assignment 1 solution


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1. (1pt) What are the advantages and disadvantages of
circuit-switched network and packet-switched network?
2. (2pt) Consider sending a packet from a source host to a
destination host over a fixed route. List the delay
components in the end-to-end delay. Which of these
delays are constant and which are variable?
3. (2pt) What is the difference between transmission delay
and propagation delay? Will the length of the packet affect
the propagation delay and why?
4. (5pt) Consider the following institutional network system.
Suppose the average object size is 100k bits and the
average rate from browsers to origin servers is 15
requests/sec. (ignore the LAN delay in the following
Assume that �”##$%% = 1.5 Mbps and the RTT on the
Internet side of the access link is 2 sec.
a. Considering the queueing delay in the access router,
the access delay could be calculated with the
equation �”##$%% =
(2345″667# 794$9%74:)
. �<5″9%
represents the transmission delay at the access link.
Without web cache, what is the total average
response time?
b. Compare this result with the situation where
�”##$%% = 100 Mbps.
5. (5pt) Two hosts, A and B, are directly connected via a link
� = 1 Mbps. The distance between A and B is 10,000
kilometers and the propagation speed over the link is
2.5 × 10A m/s.
a. How long does it take to send a file of 20,000 bits
from A to B?
b. Suppose now the file is broken up into 5 packets with
each packet containing 4,000 bits. Suppose that each
packet is acknowledged by the receiver and the
transmission time of an acknowledgment packet is
negligible. Finally, assume that the sender cannot
send a packet until the preceding one is
acknowledged. How long does it take to send the file?
c. Now assume there are two separate links between
host A and host B, i.e. �2 = 500 kbps and �C = 10
Mbps. Roughly, how long does it take to send the
same file?
6. (extra credit – 3pt) Referring to problem 4, suppose the
local web cache satisfy 60% of the requests, the remaining
40% requests will be satisfied by the origin web servers.
What is the total response time in this case?