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(COMP361)Fall02_Midterm1.pdf
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COMP 361 Computer Communications Networks
Fall Semester 2002
Midterm Examination 1
Date: October 10, Time 16:30pm : 17:50pm



Instructions:
1. This is a closed book exam

2. This examination paper consists of 5 pages and 8 questions

3. Please write your name, student ID and Email on this page.

4. For each subsequent page, please write your student ID at the top of the page in the space provided.

5. Please answer all the questions within the space provided on the examination paper. You may use the back of the pages for your rough work.

6. Please read each question very carefully and answer the question clearly and to the point. Make sure that your answers are neatly written, readable and legible.

7. Show all the steps you use in deriving your answer, where ever appropriate.

8. For each of the questions assume that the concepts are known to the graders. Concentrate on answering to the point what is asked. Do not define or describe the concepts.



Question
Points
Score

1
10


2
15


3
15


4
15


5
15


6
10


7
5


8
15



TOTAL
100





Answer the following true/false questions by circling either T or F (10 points)

(a) Connection oriented .transfer is usually unreliable.

(b) Connectionless service does not possess flow control .

(c) Video conferencing applications have approximately equal bandwidth requirements as the voice-only conferencing applications.

(d) WWW applications and file transfer applications require logical channels that guarantee that every message sent from the sender is received properly by the receiver.

(e) Packet switching uses statistical multiplexing.

(f) Fiber-optical link between Hong Kong and USA has the Round Trip Propagation delay less than 1ms.

(g) Every layered network architecture must have at least host-to-host communication layer and process-to process communication layer.

(h) Software which runs in network switches must minimize the number of times the memory is accessed during the processing of the packet.

(i) The ADSL (asymmetric digital subscriber line) bandwidth is dedicated rather than shared while HFC (hybrid fiber coax) network bandwidth is shared.

(j) HTTP servers listen for the clients requests on protocol port 80..

2. Suppose within your Web browser you click on a link to obtain a Web page. Suppose that the IP address for the associated URL is not cached in your local host, so that a DNS look-up is necessary to obtain the IP address. Suppose that n DNS servers are visited before your host receives the IP address from DNS; the successive visits incur a RTT of RTT1,, RTTn. Further suppose that the Web page associated with the link contains exactly one object, a small amount of HTML text. Let RTT0