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THE HONGKONG UNIVERSITY OF SCIENCE & TECHNOLOGY
COMP361: Computer Communication Networks I

Fall Semester, 2004
December 21, 2004

FINAL EXAMINATION
STUDENT NAME: __________________________________
STUDENT NUMBER: __________________________________
LAB NUMBER: __________________________________

Instructions to Students
1.
There are 7 problems and 10 pages. Check that you have all 10 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 30 minutes.

8.
Stop writing immediately when the time is up.



For Grading Purpose Only
Problem 1 _______________ / 15 Problem 2 _______________ / 10 Problem 3 _______________ / 15 Problem 4 _______________ / 15 Problem 5 _______________ / 15 Problem 6 _______________ / 15 Problem 7 _______________ / 15
TOTAL: ______________ / 100
Problem 1 (15 points) (Justify all your answers)
Consider a network using a link state routing protocol. Given that Router v receives the
following like-state packets from other routers.

Link-state packet from Neighbor nodes (Link Cost)
y v(1) t (4) x (6)
t v (9) y (4) s (1) u (2)
s t (1) u (4)
x y (6) v (3) w(1)
w x (1) v (1) u (3)
u w (3) v (1) t (2) s (4)

i) Construct the topology of the network from the link-state packets given in the above

ii) With the topology you have constructed, use Dijkstras shortest-path algorithm to compute the shortest paths from v to all other nodes. (Show your steps) (10 marks)

Problem 2 (10points) (Justify all your answers)
Assume router R is connected to two networks with two interfaces. On interface 1 the MTU size is 1500 bytes whereas on interface 2 the MTU size is 532 bytes.
Router R

i) Give a concise and clear definition of the MTU (4 marks)
MTU stands for Maximum transfer unit it defines the largest payload that can be carried in a link layer frame (data field) by a given network. The MTU includes the IP header but does not include the Link layer header.
ii) Assume that router R receives an IP packet on interface 1 and determines that the packet must be forwarded on Interface 2. Explain clearly and briefly what should the router do if the packet header (in hexadecimal) were: (6 marks)
45 00 05 DC 08 DB 00 00 40 06 CE F1 8F 59 56 7B 8F 59 28 22

For reference the IP header format is given below.
0 4 8 1619 31
V ersion HLen TOS Length
Ident 0 df mf Offset
TTL Protocol Checksum

SourceAddr
DestinationAddr
Checksum (CEF1) is correct, TTL (40) is larger than 1, therefore, since the datagram length
(