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(COMP361)final-f03_sol.pdf
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COMP 361 Computer Communications Networks
Fall Semester 2003
Final Examination: Solution key
Date: Dec 15, 2003, Time 8:30am - 11:30am, venue Rm 3007
Name:______________________Student ID:________________Email:_______________
Instructions:
1.
This examination paper consists of 14 pages and 11 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 unless specifically asked to.


Question Points Score
1 8
2 7
3 10
4 12
5 15
6 15
7 10
8 6
9 5
10 6
11 6
TOTAL 100

1) Answer the following true/false questions by circling either T or F. (8 points)
a) BGP is the unique Inter-AS routing protocol available on the Internet (an Inter-AS protocol is one that routes between Autonomous Systems).
b) Head of Line (HOL) blocking can result in output buffer overflow in routers
c) Slotted Aloha is more efficient than pure Aloha
d) An IP datagram that will be transported using the ATM AAL5 protocol will be padded so that its length will always be a multiple of 48 bytes
e) Host A is sending host B a large file over a TCP connection. Assume Host B has no data to send to A. Host B will not send acknowledgements to host A because host B can not piggyback the acknowledgements on data.
f) Consider Congestion Control in TCP. When a timer expires at the sender, the threshold is set to one half of its previous value.
g) The Date: header in an http response message indicates when the object in the response was last modified.
f) A two-dimensional parity check scheme can detect the occurrence of up to two bit errors in the original data.
T F
T F
T F
T F
T F
T F
T F
T F

2) Consider a link of rate R Kbps carrying eight identical ongoing client /server applications, with each of the applications using one TCP connection.
a) If new application X comes along and opens one new TCP connection what transmission rate will it get? Explain your answer. (2 points)
b) If it wants to acquire a rate of R/2, how many TCP connections does it have to open? Explain your answer. (2 points)
c) Following up on (b); if the original 8 client/server applications with one TCP connection each all leave the link and 8 new UDP based applic