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(COMP361)mid-term 2007-solution.pdf
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COMP 361 Computer Communications Networks I

Spring Semester 2007

Midterm Examination

Date: March 23, 2007 Time: 6:00 pm C 8:00 pm

Name:
_______________
Student ID:
_______________
Email:
_______________





Instructions
1. Please write your name, student ID and email address on this page.

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

3. Please answer all questions within the space provided on the examination paper. Please be concise.

4. This paper consists of 6 questions and 12 pages.

5. Please read each question very carefully and answer the questions 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
15


4
15


5
20


6
20


TOTAL
100





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

a) Go-Back-N buffers out of order packets at the receiver, while Selective Repeat ignores them.


T F
(wont corrupt!!)(wont corrupt!!)(wont corrupt!!)(wont corrupt!!)
b) While using email clients (e.g., Outlook Express, Foxmail) to send emails, these applications will connect directly to the receivers mail server and push the email into their mailbox via SMTP protocol.


T F

c) To make sure that packets are correctly transferred on the links from source to destination, TCP is implemented at every hop in a route.


T F

d) FTP and SMTP are called all out-of-band protocols and HTTP is called in-band protocol.


T F

e) For queuing delay analysis part, if traffic density larger than 1, then the average rate at which the bits can be transmitted from the queue exceeds the rate at which the bits arrive at the queue.


T F

f) A Selective Repeat protocol can achieve better performance than a Go-back-N protocol, so TCP uses the Selective Repeat protocol instead of the Go-back-N protocol.


T F

g) The delay in packet-switched n