University of California, IrvineEECS 148 2013 Final Exam Solutions-VERIFIED BY EXPERTS 2021
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Course
INTRODUCTION TO COMPUTER NETWORKS (EECS148)
Institution
University Of California
Introduction to Computer Networks
Fall 2013 CompSci 132/EECS148
Sample Final Exam - Solution Sketch
(Friday, Dec. 13th, 2013, 1:30-3:30pm)
Open books, open notes. Computers and cellphones should be turned off.
Student’s Last Name:
Student’s First Name:
Student ID:
Email:
Problem # Poin...
Prof. Athina Markopoulou Introduction to Computer Networks
Fall 2013 CompSci 132/EECS148
Sample Final Exam - Solution Sketch
(Friday, Dec. 13th, 2013, 1:30-3:30pm)
Open books, open notes. Computers and cellphones should be turned off.
Student’s Last Name:
Student’s First Name:
Student ID:
Email:
Problem # Points Out of Total
1 20
2 20
3 30
3 30
Total 100
Academic Honesty Policy:
I agree to abide by the UCI Academic Senate Policy on Academic Honesty (Appendix VIII.B),
which specifies that students have responsibility for:
1. Refraining from cheating and plagiarism.
2. Refusing to aid or abet any form of academic dishonesty.
3. Notifying professors and/or appropriate administrative officials about observed incidents of
academic misconduct. The anonymity of a student reporting an incident of academic dishon-
esty will be protected.
Student’s Signature:
GOOD LUCK!
1
, 1. (20 Points) TCP. Consider the following plot of TCP window size as a function of time
(counted in # RTTs). The coordinate of each turning point has been marked in the plot.
!
Answer: See figure below for an overview of the answer.
45 I
--.
I I I I I I I I
SS(0,
I 4.5) ICA(4.5, 12)
I SS(13,
I 17)
I ICA(17,
I 26)I I
40 ___i _L I L ____! I ___l I _j
I I I I I I I I I
I I I I I I I I I I
(/) I I I I I I I I I I
(/)
35 I I I (12, 32)1 I I I I I
I I I timeout
I I I I I I
I I I I I I I I
=It
..._. 30 I I I I I I I I I
Q)
·-N ssthresh
I
I
= 25 I I
I I
I
I
I
I
I
I
I
I
I I
I (26,25)
I
(/) 25 I I I I ---, I---, I - I
I (4 .5, 25) I I I I I I I I
0 I I I I I I I I (24,23)
I I
""C
c: 20 --r I I I II r--'I I -I
·-
sc: 15 ---t
I
I
I
I
---t-
I
I
I
I
ssthresh
I
I
I
I = 16
-t- --t
I
I
I
(17,16)
I I
t - --t
I
I
I -I
I
I
0 I I I I I I I I I I
·- I I I I I I I I I I
(f)
Q)
C)
10 -+ 4 I I +- ---4 ---4 I - I
I I I I I I I I I
c: I I I I I I I I I
0
0 5 -+- I I +--- ----4 I - I
I I I I I I I I I
(0 , 1) I I (13, 1) I I I I I
0 2 4 6 8 10 12 14 16 20 22 24 26
More specifically: Time (#RTT)
(a) (5) Identify the intervals of time when TCP slow start is operating. What is the respec-
tive SSThres (slow start threshold) in TCP congestion control?
Answer: These are the periods of exponential increase: (0,4.5) and (13, 16). The SSThres
are 25 and 16, respectively, i.e, the values at which the increase switches from exponential
to linear.
(b) (2 Points) Identify the interval(s) of time when TCP congestion avoidance is operating.
What is the respective SSThres?
Answer: It is the period of linear increase: (4,5, 12). The SSThresh is 25.
(c) (3 Points) How many segments are lost from time 0 to 16?
Answer: at least one 1 packet at time 12 triggered a timeout. There is no other time of
loss on this diagram.
(d) (10 Points) Assume that no packet is lost during time 16-26. Complete the TCP con-
gestion window curve from time 16 to 26.
Answer: The critical turning point is at (17,16) where the congestion window reaches
the SSHThresh value ( 32 2 = 16 and switches from exponential to linear increase.
2
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