School of Professional Education and Executive Development
Assignment Question Paper
Subject Code : SEHS3321
Subject Title : Computer Network Administration
Semester & Academic Year : Semester One, 2019/20
Submission Deadline to
Moodle
: 13 December 2019 11:00 AM
Turnitin Submission is Required: [Yes / No]
This assignment question paper has a total of FIVE pages (including this covering page).
Declaration of Original Work
Plagiarism is a serious misconduct. No part of students’ assignment should be taken from other
people’s work without giving them credit. All references must be clearly cited. Any plagiarism
found in students’ completed assignments can lead to disciplinary actions such as mark
deduction, disqualification or even expulsion by the School.
Prior to your submission, you MUST sign the “Declaration of Original Work” (template to be
provided in Moodle) on the covering page of your completed assignment indicating that the
work you have completed is your original work. The signed declaration must be submitted with
your assignment.
Format
You MUST include (a) full student name, (b) student number, (c) subject code, (d) subject group
(e) page number and (f) total number of pages on EVERY answer sheet.
Page 2 of 5
Question 1
Alice (alice@ABCmail.com) sends an email to Bob (bob@XYZmail.com), and Bob reads the
email successfully. What application layer protocol(s) is/are used? Describe the activities involved
by the protocol(s). (7 marks)
Question 2
Consider the P2P session below. The upload and download rates are in terms of Mbps. Assume
there is no delay in the network core, and all hosts participate in the entire session. Calculate the
time required for all hosts to get the file of size (n x 100) Mb, where n is the last digit of your
student ID number. Set n to 10 if the last digit is 0. Show your steps. (5 marks)
Question 3
In the TCP session below, suppose the starting sequence number is n, where n is the first 4 digits of
your student ID number (e.g. 1912). Determine the sequence numbers of all Data packets, and the
acknowledgement numbers of all ACK packets. (6 marks)
Data(1): 320 bytes
Data(2): 260 bytes
Data(3): 180 bytes ACK(a)
ACK(b)
ACK(c)
Data(2): 260 bytes
X
Timeout
(n x 100) Mb
Page 3 of 5
Question 4
The IP datagram with size (3000 + n x 100) bytes, including the header 20 bytes, arrives at a router.
The MTU of the router’s outgoing link is 1300 bytes. Suppose n is the last digit of your student ID
number. State the value of length, fragment flag and fragment offset of all fragments created by the
router. Show your steps. (10 marks)
Question 5
Given the network topology below in Packet Tracer, and Router 1 is just booted with the default
startup configuration. What commands should you use to configure Router 1 and setup OSPF
routing? (12 marks)
Question 6
Consider that you are going to visit the web page “http://www.secret.com/examtips/index.html” for
the first time. The web page shows two pictures (tips1.jpg and tips2.jpg) on the screen, each with a
hyperlink to download a document file. There was no cache in your PC and in the web cache of
your network. The DNS hierarchy is given below:
root
local DNS server .edu .com
dns.secret.com
(authoritative)
(a) Suppose there is no cached record in all DNS servers. Describe how your browser obtains the
IP address of the web server using iterated query. (6 marks)
(b) Suppose HTTP version 1.1 is used. Write the request line and Host field of the header of HTTP
request message for requesting the page index.html. (4 marks)
(c) HTTP version 1.1 adopts persistent HTTP. By using a time diagram, illustrate the HTTP
messages exchange between your browser and web server until the web page is displayed.
(5 marks)
Question 7
The figure above demonstrates the change in congestion window size of a TCP Reno sender. The
initial threshold is set to 16 segments.
(a) What are the TCP states in rounds 1 to 5, in rounds 5 to 9 and in round 10? (3 marks)
(b) The window size was reduced after round 9 and after round 16. What was happened and how
did TCP Reno handle such situation? (8 marks)
(c) Suppose all segments in round 20 were transmitted successfully. What should be the window
size in round 21? (1 mark)
(d) How is TCP Reno different from TCP Tahoe? Indicate the round number that the operation will
be different if TCP Tahoe is used. (3 marks)
Page 5 of 5
Question 8
Consider the network topology below. There are four routers in the network, with the number next
to a link indicating the cost of using that particular link.
(a) Routing algorithm can be classified into link state and distance vector. What are the differences
between them? (4 marks)
(b) Suppose distance vector algorithm is used. What is the initial distance vector maintained in each
router? (4 marks)
(c) Demonstrate the distance vector updates in the network until the algorithm converges.
(7 marks)
Question 9
Consider that you are in a classroom and connect to the college wireless LAN using WiFi. There
are some mobile users in the same BSS with you. The college network is protected by intrusion
detection system (IDS).
(a) Describe the hidden-terminal problem and exposed-terminal problem in a wireless network, and
how CSMA/CA can handle these problems. (8 marks)
(b) If you move to another classroom, you connect to another BSS, but you still remain in the
college LAN with the same IP address. Why can this happen? (3 marks)
(c) Explain how IDS protects the network and why it is better than firewall. (4 marks)