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(COMP361)example_final_spr05.pdf
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COMP 361 Computer Networks
Spring Semester 2005
Final Examination
Date: May 21, 2005 Time: 12:30 am C 3:00 pm

Name:_____________________ Student ID: ________________Email:__________________
Instructions
1.
Please write your name, student ID and email address on this page.

2.
Please answer all questions within the space provided on the examination paper. You may use back of the pages for your rough work. Please be concise, and this is NOT an essay contest.

3.
This paper consists of 5 questions and 9 pages.

4.
You have total 150 minutes to complete exam, thus each 10 points question roughly requires 15 minutes, please manage your time wisely.

5.
Please read each question very carefully and answer the questions carefully and clearly to the point. Make sure your answers are neatly written, legible, and readable.

6.
Show all the steps used in deriving your answer, wherever appropriate.


Question Points Score
1 10
2 20
3
4
5
Total 100

1. Answer the following true/false questions by circling either T or F [10 points]
a) The Token Ring network achieves better utilization than CSMA/CD
under heavy traffic load T

F b) Both Router and Switch are plug-and-play devices T F c) RIP (Routing Information Protocol) use Distance vector algorithm, where
advertisements are sent in TCP packets. T F d) Error correction is provided in the transport layer. T F e) A hub is a physical layer repeater and a switch is a store-and-forward device. T
F f) OSPF is the only intra-AS routing protocol (an intra-AS is a protocol that routes packets within an Autonomous System) use in the Internet. T F g) Class-C networks contain 24-bit subnet addresses. T
F h) Doubling the Time Interval in TCP is a mechanism applied for Flow Control T F i) FTP uses out-of-band control and runs on top of TCP. T
F
j) The Simple Mail Transfer Protocol (SMTP) enables the mail receiver to receive the mail from the mail recipient mail server. T F
2. Please briefly answer the following questions. Please be concise, and each answer preferably uses less than 2-3 sentences
a) Briefly explain: what is the meaning of 'good news travels fast' in DV algorithm and what is the count to infinity problem.
Answer:
In DV algorithm, good news travels fast means when the link cost decreases, the distances vector table at the nodes may converge very quickly. The count to infinity problem happens when a link cost increases. The algorithm needs to perform a great amount of iterations before it stabilizes.
b) List the main steps of CSMA/CD protocol. Assume the node always has Ethernet frame to send in its adapter buffer.
Answer: STEP 1, if the adapter senses that the channel is idle, it starts to transmit the frame. If the channel is busy, it waits until it senses no signal energy and then starts to transmit the frame.
STEP 2, While transmitting, the adapter monitors the presence of signal energy from