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(ELEC315)[2009](f)midterm~419^_10323.pdf
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ELEC 315: Computer Communications Networks
Prof. Tsang, Danny H. K.
(Fall 2009)

Department of Electronic and Computer Engineering
The Hong Kong University of Science and Technology

Mid-Term Examination Solution
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PROBLEM 1 (20 points)

Multiple Choices
For each of the following questions there maybe one or multiple correct answers. Please write down the correct answers in your answer book. You will receive 2 points for each correctly answered question, 0 point if you leave it blank, and a penalty of minus 2 points for each incorrectly answered question.

1. In the transmitting process of packet X from host A to host B, which of the following delays are proportional to the size of packet X? a. Processing delay

b. Queuing delay

c. Transmission delay

d. Propagation delay

e. None of the above





Answer: c


2. According to the five-layer internet protocol stack, protocols of which layers are implemented in the local machine? a. Application layer protocols

b. Transport layer protocols

c. Network layer protocols

d. Link layer protocols

e. Physical layer protocol

f. None of the above





Answer: a, b, c, d, e


3. Which of the following E-MAIL protocols are pull-based protocols? a. SMTP

b. IMAP

c. POP3

d. HTTP

e. None of the above





Answer: b, c, d


4. Your computer will not be able to connect to other machines on the Internet if the domain name server that your machine attempts to use is down. a. True

b. False





Answer: b

5. When a HTTP browser visits a webpage stored in a non-persistent HTTP server and the webpage includes 10 reference objects, how many TCP connections are established between the client and the server in order for the browser to display the webpage? a. 1

b. 2

c. 10

d. 11

e. 12





Answer: d

6. Is it possible for an application to achieve reliable data transmission if it uses UDP in the transport layer? a. Yes

b. False





Answer: a


7. What is the range of the well-known ports? a. 1~1023

b. 1~1024

c. 0~1023

d. 0~1024

e. None of the above





Answer: c

8. In what case will a TCP sender perform a fast retransmit? a. Receives 2 duplicate ACKs

b. Receives 3 duplicate ACKs

c. Receives 4 duplicate ACKs

d. None of the above





Answer: b

9. In TCP connection establishment procedure (three-way handshake), which of the following statements are true? a. In step 1, the 1 bit ACK field in TCP segment header is 0

b. In step 2, the 1 bit SYN field in TCP segment header is 0

c. In step 2, the sequence number in TCP segment header is always chosen as 0

d. In step 3, the data field in TCP segment may contain the data from application layer

e. None of the above





Answer: a, d

10. In TCP congestion control, which