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(COMP361)Fall02_Final.pdf
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COMP 361 Computer Communications Networks
Fall Semester 2002
Final Examination
Date: December 16, Time 16:30pm : 19:30pm , venue Room 3007




Instructions:

1. This examination paper consists of 7 pages and 7 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.



Question
Points
Score

1
10


2
10


3
15


4
10


5
20


6
20


7
15



TOTAL
100






Name:______________________Student ID:________________Email:_______________

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



(a) ATM cell size is 64 bytes

(b) AAL5 uses only 44 bytes of the ATM cells payload.

(c) Spanning tree algorithm is needed to prevent loops in extended LANs obtained by interconnected LANs with bridges.

(d) Domain Name Servers dont use caching to improve performance. They perform full name resolution each time they receive a name resolution request.

(e) In FDDI network when token is late, the station is forbidden to send both asynchronous and synchronous frames.

(f) Maximum segment size MSS at the TCP layer should be related to maximum data link frame size in order to avoid IP fragmentation.

(g) The Ethernet network uses CSMA/CD algorithm which is 1-persistent.

(h) When collision occurs in the CSMA/CD network, the time needed for the station to learn about the collision is limited by the round trip propagation delay of the cable plus the delay through repeater(s).

(i) ICMP messages can not be lost by the network.

(j) The Link-state routing algorithm, requires small memory space when it is running in both small and large networks.




2. Answer the following questions : (10 points)





a) What does a router do with time to live value in an IP header if the current hop is not the last routing hop? Does this affect any other field in the IP header? Which? (5 points)



Answer: If the destination does not match any of the local machines addresses, IP decrements the time to live field in the IP datagarm header, discarding the datagram if the cont reaches z