CS 455: Computer Networks and Data Communication Sample Final Examination Points: 125

CS 455: Computer Networks and Data Communication
Sample Final Examination
Points: 125
Time allowed: 180 minutes
CLOSED BOOK, CLOSED NOTES, OPEN MIND
Answer All Questions
(Note: This sample exam does not cover Chapter 8. But the final exam
does cover it. Make a note of this.)
Turning in this exam under your name confirms your continued
support for the honor code of Old Dominion University and further
indicates that you have neither received nor given assistance in
completing it.
Name: ______________________________ SSN: _________________
Question #
1
2
3
4
5
Bonus
Total
Possible points
25
25
25
25
25
5
125
Obtained points
FINAL ANSWER SHOULD BE WRITTEN IN THE ALLOTTED
TABLES.
CS 455: Sample Final Examination
1
Question 1:
a. Using Dijkstra’s shortest path algorithm, determine the shortest distance and shortest path
from A to F. (Start the algorithm from node A). Show your work. (For your reference, a
description of the algorithm is reproduced from the book in the appendix.)
B
10
A
3
5
D
4
E
17
2
F
6
12
7
C 2
G
b. If flooding is used as a routing algorithm to send a packet P from node A to F (in the below
network), show the flow of packet P from A to F. (Show all flows due to P from A)
B
D
E
A
F
C
G
c. Using distance vector routing, compute the new routing table at B (in the above network)
when it has received the following tables from A, D, and E. The delay from B to A, D, and E is
2, 5, and 5, respectively.
A
0
10
3
15
1
12
10
D
10
8
15
0
13
3
5
4
5
9
11
0
4
4
E
CS 455: Sample Final Examination
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Question 2:
a. Using the following network diagram, show how hop-by-hop choke packets may be used to
slow down the sender node A that is currently sending packets to node F using the path A-CG-F.
B
D
E
A
F
C
G
b. An application produces output in terms of 2-Mbyte bursts. Each burst has a 20 milliseconds
duration, and bursts occur at a constant interval of 500 milliseconds (i.e., 2 in a second). The
application lasts for 2 seconds. It is connected to an 8-Mbps network through a token bucket.
Suppose the token bucket is initially filled to capacity with 12 Mbits, show (schematically) the
variation in the output from the token bucket until all the application data is transmitted. Tokens
arrive into the bucket at the rate of 5Mbps. (Note: Assume that each token allows 1 bit.)
c. Convert the IP address whose hexadecimal representation is D22C1470 to dotted decimal
notation.
CS 455: Sample Final Examination
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Question 3:
a. A packet was sent from node A to node F using IP protocol. It was fragmented as follows along
the way (at nodes C and G). What are the value of fragment offset, DF, and MF fields for F1,
F2, and F3 when received at node F?
1000
Node A
300
300
F1
700
360
F2
Node C
340
Node G
F3
Node F
b. A company uses NAT (Network Address Translation) to connect multiple workstations (WS)
to the internet using a single IP address (203.45.103.67) provided by its ISP. Show how packets
sent from a specific WS (10.23.52.201) to another workstation (125.25.43.98) are handled by the
NAT. (Use the specific data given. Don’t simply write some generic answer.)
WS
NAT
10.23.52.201
ISP Router
203.45.103.67
WS
125.25.43.98
c. What are the implications of not having a checksum field in the IPv6 header? What happens
when a packet is received in error at the destination?
CS 455: Sample Final Examination
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Question 4:
a. How do you explain the absence of source address and destination address fields in the
TCP header?
b. Host H1 intends to establish a TCP connection with host H2. List the sequence of steps
that take place at H1 and H2 before H1 starts sending its data on the connection.
c. Explain the significance of the following three states in the TCP connection management
finite-state diagram.
(i) FIN WAIT 1 (ii) FIN WAIT 2 (iii) TIME WAIT
CS 455: Sample Final Examination
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Question 5:
a. The timer management module of a TCP connection had an initial estimate of RTT of 20
milliseconds and a deviation of 5 milliseconds. It has a smoothing factor of 0.7. It is then
observed that the next two TPDUs had an RTT of 40 and 10 milliseconds, respectively.
Determine the current values of RTT, D, and timeout values (after both TPDUs were
received).
b. What problem does Nagle’s algorithm solve? How does it solve the problem?
c. What is silly window syndrome? How does Clark’s algorithm solve this problem?
CS 455: Sample Final Examination
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