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(COMP361)midterm_fall03_sols.pdf
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COMP 361 Computer Communications Networks
Fall Semester 2003
Midterm Examination
Date: October 23, 2003, Time 18:30pm --19:50pm





Instructions:
1. This is a closed book exam

2. This examination paper consists of 8 pages and 7 questions

3. Please write your name, student ID and Email on this page.

4. For each subsequent page, please write your student ID at the top of the page in the space provided.

5. 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. Each question is on a separate page. This is for clarity and is not meant to imply that each question requires a full page answer. Many can be answered using only a few lines.

6. 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.

7. Show all the steps you use in deriving your answer, where ever appropriate.

8. 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 unless specifically asked to do so.



Question
Points
Score

1
10


2
10


3
10


4
15


5
15


6
20


7
20



TOTAL
100




Name:______________________Student ID:________________Email:_______________









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

(a) The FTP protocol runs on top of TCP. T

(b) DNS runs on top of TCP F

(c) If HTTP uses persistent TCP connections only one object can be transferred over the connection before closing it. F

(d) UDP does not provide a congestion control scheme. T

(e) If a name server is authoritative for a particular hostname, it will contain a Type-A record for the hostname. T

(f) Doubling the Timeout Interval in TCP is a limited form of Flow-Control F








(g) HTTP uses out-of-band control F

(h) FTP uses out-of-band control T

(i) The user-agent (e.g., mail-reader) of the receiver of an email message uses SMTP to download the message from the receivers mailbox. F

(j) Selective-repeat protocols keep only one timer, which is used to signal timeouts of the oldest unacknowledged packet. F





















2. (10 points).
(a) Briefly explain the diff