=========================preview======================
(COMP361)midterm_fall04.pdf
Back to COMP361 Login to download
======================================================
THE HONGKONG UNIVERSITY OF SCIENCE & TECHNOLOGY
COMP361: Computer Communication Networks I
Fall Semester, 2004
October 26, 2004
MIDTERM EXAMINATION
STUDENT NAME: __________________________________
STUDENT NUMBER: __________________________________
LAB NUMBER: __________________________________
Instructions to Students
1. There are 5 problems and 8 pages. Check that you have all 8 pages.
2. Write your name, student number and Section number on this page.
3. Write your student number on each of the following pages.
4. Answer all questions in the space provided.
5. Rough work should be done only on the back pages and afterwards draw a diagonal line through it to show that it is not part of your answer.
6. Leave all pages stapled together.
7. The examination period will last for 1 hour and 30 minutes.
8. Stop writing immediately when the time is up.
For Grading Purpose Only
Problem 1 _______________ / 20
Problem 2 _______________ / 30
Problem 3 _______________ / 14
Problem 4 _______________ / 10
Problem 5 _______________ / 26
TOTAL: ______________ / 100
Problem 1 (20 points) (Justify all your answers)
Suppose a 100Mbytes per second point-to-point link is being set up between a Hospital and a center for medical imaging (CMI). The distance from the Hospital to the CMI is approximately 100 km, and data travels over the link at the speed of light of 2 x 108 m/s.
a) Calculate the minimum round-trip time (RTT) between the hospital and the CMI. (4points)
b) Using the RTT as the delay, calculate the (delay * bandwidth) product for the link. (4points)
c) What is the significance of the (delay * bandwidth) product computed above? (6points)
d) A Scanner in the CMI takes high definition medical images of the patients and saves them in digital format on a disk. Suppose a doctor at the Hospital wishes to download the latest image which is 25Mbytes. What is the minimum amount of time that will elapse between the sending of the request from the Hospital until the transfer is finished? We will assume that the request is only a few bytes and it takes a negligible time to transmit it. (6 points)
Problem 2 (30points) (Justify all your answers)
The RTT is the propagation time between the Hospital and the CMI and back
2 * 100 10^3/2 * 10^8 = 100 10^-5 s = 1 ms
The bandwidth Delay product is
10^-3 * 8 * 100 10^6 = 800 Kbits
The (delay * bandwidth) product is the amount of data required to fill the pipe.
This is the amount of data that a sender can transmit before it expects receiving a response from the receiver.
Time to send the request = transmit time + propagation time = 0 + 0.5ms
Time to send the reply = transmit time + propagation time = 25 10^6/100*10^6