Download Northeastern Illinois University Department of Computer

1
Northeastern Illinois University
Department of Computer Science
CS 331
Name: _____________________
Question 1
Question 2
Question 3
Question 4
Question 5
Question 6
Total
Final Grade
(Total *0.25)
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10
___
10
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15
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20
___
20
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25
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100
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25
Example Final Exam
Instructions: The answer to the questions should ALL be written down in space provided. Poorly written
answers will be poorly graded.
Question 1: Multiple choice (2 points for each correct answer), please select your answer by placing a circle
over the letter and justifying when asked. There is only one possible answer.
i.
Consider a subnet with prefix 128.119.40.128/26. How many bits are used for host addressing?
a) 2
b) 8
c) 26
d) 6
The Network layer receives services from which layer?
ii.
iii.
a) Transport layer
b) Data Link Layer
c) Application layer
d) none of the above
How many bytes does the UDP header have?
a) 64
b) 8
c) 16
d) 4
How many bits in a MAC address (i.e. used in most LAN with Ethernet) ?
a) 6
b) 32
c) 48
d) none of the above
Justify by drawing the header with the name and number of bytes for each field:
iv.
What is RTT?
a) propagation delay + transmission delay
b) 2 * end-to-end delay
c) end-to-end delay
d) none of the above
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Question 2: Write one sentence definition for each concept (2 points for each definition)
a) IP Router:
(2 points)
b) Subnet:
(2 points)
c) Transmission delay:
(2 points)
d) Stop-and-Wait:
(2 points)
e) Integrity:
(2 points)
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Question 3: Write a brief answer (be clear and concise)
Assuming TCP (TCP protocol discussed in class) answer the following questions and justify briefly your
answer.
a) Write in the space below the difference between congestion control and flow control.
(5 points)
b) Draw a graph that shows the saw-tooth behavior of TCP congestion control. Your graph must clearly
identify with labels the slow-start phase, when a time-out occurs, addictive-increase phase, fastrecovery, when a triple-ack occurs. You must label the graph with the correct units for x-axis and y-axis.
(10 points)
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Question 4: This question is regarding the application layer.
a) Write the name of the application layer protocol, transport layer protocol, and application architecture
used by DNS.
(5 points)
b) Suppose there is a distributed denial of service attack on DNS. Assume you are at Youngstown State
University and you know that the IP address of YSU’s web server is 150.134.10.10. How would you be
able to connect to YSU’s web server without DNS? You must write down the steps and programs you
would used to access YSU’s web server.
(5 points)
c) Draw a diagram below that will explain the steps required by DNS to resolve the HTTP request
http://www.vindy.com from a computer located in the domain www.neiu.edu. You must label ALL the
servers involved in resolving the HTTP request using recursive queries, label each domain separately,
label each query with a number indicating the order in which queries are issued and responded by the
servers.
(10 points)
5
Question 5: Answer the following questions with short answers:
a) Given an IP address 198.64.12.13 and subnet mask of 255.255.255.0. Determine the network address.
You must write the binary representation of each element to obtain full credit for your answer.
(5 points)
b) Consider the ARP protocol and how IP addresses are mapped to MAC address. Carefully study the
picture below and answer the following questions assuming host A is sending a packet to host B
i.
Describe briefly what the ARP protocol is about?
(5 points)
ii.
What is the MAC address of host A?
(5 points)
iii.
Write down in the space below the MAC address the router (R) reads from A’s frame when
the packet arrives at the router (R).
(5 points)
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Question 6: Write the solution to the following problems
a) Explain CSMA/CD (Carrier Sense Multiple Access with Collision Detection) in your own words by
describing the steps that a computer most follow to transmit a frame. You must consider the scenarios
were a collision occurs and the scenarios were there is no collision.
(5 points)
b) We would like to compare the performance of the STOP-AND-WAIT protocol versus the GO-BACK-N
protocol. Assume we are sending fives packets numbered from one to five; assume there is no loss in the
channel except when packet three and packet five were send for the first time.
b.1) Draw the protocol diagram for each protocol.
(10 points)
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b.2) Write the total response time and overhead for each protocol.
(10 points)
Extra Credit: (10 points)
Consider all the concepts you have learn in this class listed below. Rank the list of topics and explain
why you think these topics are an essential learning outcome for this class.
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•
•
•
•
•
•
•
•
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Delay
Protocol
Internet Protocol Stack
Packet Switching
DNS
Peer-to-Peer Architecture
Security: Confidentiality, Integrity, and Availability
Reliable Data Transfer
TCP and UDP
Deterlab