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(COMP361)final-s04_sol.pdf
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COMP 361 Computer Communications Networks
Spring Semester 2004
Final Examination C Solution Key
Date: May 24, 2004. Time: 4:30pm C 7:30pm. Venue: Rm LG4204
Name:______________________Student ID:________________Email:_______________
Instructions:
1.
This examination paper consists of 17 pages and 10 questions

2.
Please write your name, student ID and Email on this page.

3.
For each subsequent page, please write your student ID at the top of the page in the space provided.

4.
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.

5.
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.

6.
Show all the steps you use in deriving your answer, where ever appropriate.

7.
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 unless specifically asked to.


Question Points Score
1 8
2 15
3 6
4 15
5 15
6 8
7 8
8 5
9 5
10 15
TOTAL 100

1) Answer the following true/false questions by circling either T or F. (8 points) 2) (15pts)
a) OSPF is the only Intra-AS routing protocol (an Intra-AS protocol is one that routes T F
within Autonomous Systems) in use today
b) Bridge forwarding is cut-through. T F
c) Slotted Aloha is more efficient than pure Aloha T F
d) PPP uses a CSMA access-control protocol T F
e) ATM is an end-to-end (desktop-to-desktop) network protocol T F
f) In Selective Repeat protocols the loss of one packet can force the retransmission of T F
many correctly received packets.
g) Domain Name Servers don't use caching to improve performance. They perform full T F
name resolution each time they receive a name resolution request.
h) A two-dimensional parity check scheme can correct all two-bit errors in the original T F
data.

a) What is meant by the Hidden Terminal problem? Why is this a problem?
b) Draw a diagram illustrating the Hidden Terminal Problem (you must explain how your diagram illustrates the problem.)
c) The 802.11 Wireless LAN protocol suite uses CSMA/CA (Collision Avoidance) to help solve the hidden terminal problem.
Explain how CSMA/CA works and why it solves the hidden terminal problem.
When explaining how CSMA/CA works you should assume a scenario in which there is a wireless network with (i) a sender, (ii) a receiver and (iii) other nodes. You should describe the actions taken by all of the members of the network when implementing the protocol.
(Note: in your explanation of how CSMA/CD works you do not have to write the formal technical names of all of the packets sent, but you do need to describe their functions.)
a)