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(COMP361)Final-exam-361-2005-fall.pdf
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THE HONGKONG UNIVERSITY OF SCIENCE & TECHNOLOGY
COMP361: Computer Communication Networks I
Fall Semester, 2005
Tuesday, December 13, 2005

Final EXAMINATION

STUDENT NAME: __________________________________
STUDENT NUMBER: __________________________________
LAB NUMBER: __________________________________



Instructions to Students

1. There are 6 problems and 8 pages. Check that you have all 8 pages.

2. Write your name, student number and Section number on this page.

3. Write your student number on each of the following pages.

4. Answer all questions in the space provided.

5. Rough work should be done only on the back pages and afterwards draw a diagonal line through it to show that it is not part of your answer.

6. Leave all pages stapled together.

7. The examination period will last for 2 hour and 45 minutes.

8. Stop writing immediately when the time is up.




For Grading Purpose Only
Problem 1 _______________ / 15

Problem 2 _______________ / 20

Problem 3 _______________ / 10

Problem 4 _______________ / 20

Problem 5 _______________ / 20

Problem 6 _______________ / 15


TOTAL: ______________ / 100

Problem 1 (15 points)

Consider a network using the link state and consider that router E receives the following link state packets from other routers in the network

LSP from node
Neighbor node (link cost)

B
A(1)
D(15)
E(5)


C
A(2)
D(1)
E(2)


D
B(15)
C(1)
E(10) A B C


E
A(16)
B(5)
C(2)
D(10)




a) Construct the network topology from this table. [3 points]
Subtract 0.5 for each missing link or link cost upto a maximum of 3 points.

b) From the topology you have constructed, use Dijkstras algorithm to compute the shortest path from node A to all other nodes in the network. [10 points]




Set N
B
C
D
E

From A
to
Via
Path Cost

A
1,A
2,A
Inf
16,A
B
A
1

A,B

2,A
16,B
6,B
C
A
2

A,B,C


3,C
4,C
D
C
3

A,B,C,D



4,C
E
C
4

A,B,C,D,E










1 point for each correct value in the shaded boxes and 2 points for the shortest paths (given explicitly in any way possible without ambiguity)

c) Assume now that router D received the same LSPs as node A. If A sends a TCP packet to router D does the ACK packet from D to A take the same path as the TCP packet? Why? [2 points]




Yes, because LS is a global algorithm where all nodes use the same topology and the links are symmetric. So the least cost path from A to D is also the least cost path from D to A



16





Problem 2 (20 points) (Justify all your answers)

a) Consider the following network topology, and assume the network uses the distance vector routing algorithm.