COMP247 Data Communications
Assignment 2, 2016
Due: Tuesday 31st May, 2016, 6 pm
This assignment is designed to help you develop skills and strengthen your
understanding of data communications. Answer the questions as if they are a
professional presentation to a client. Thus justify what you say in terms of what will
work well for the client. Your submission should be around 5 to 10 pages, but be
succinct. Your assignment will be submitted electronically as below with TurnItIn
on the COMP247 iLearn page.
Before doing assignment 2, please read the Assignment 1 Comments and the
following Assignment Typography document in 14 Assignment Specifications on
the COMP247 iLearn page. You will lose marks if these guidelines are not followed
– or to put it more positively, these guidelines are to help you get the best marks.
Question 1 (20 marks) – Physical Layer
Part A We presented four impairments to physical transmission of signals – attenuation,
noise, attenuation distortion, and delay distortion. How will these affect the guided media
of copper wires and optical fibre cable, and wireless media? Suggest some techniques that
are used at the physical layer to counteract these effects (that is ignore techniques like error
detection and correction used at higher layers).
Part B Consider again the above three media, but in this case how does security affect
these media and again what physical measures can be taken to secure these media.
Question 2 (20 marks) – Wireless LAN
Boojum Enterprises intends letting their workers bring their own device (BYOD) to work,
so that workers can use a device that they are personally comfortable with. The office
measures 50 metres by 20 metres. It is already serviced by a 1000Base-T Ethernet LAN.
What would you recommend for a wireless LAN installation? What 2016 802.11
technology would you recommend? How many access points are required and how would
they be positioned for the particular version of 802.11 you have chosen?
Question 3 (10 marks) – Backbone Networks
A backbone network can be constructed as a switched backbone, a routed backbone or a
VLAN backbone. Each of these approaches has its advantages and disadvantages.
a) (6 marks) Discuss the advantages and disadvantages of each approach. [Up to 400
b) (2 marks) Describe an example of a situation where a switched backbone would be
preferred. [Up to 150 words]
c) (2 marks) Describe an example of a situation where a VLAN backbone would be
preferred. [Up to 150 words]
Question 4 (10 marks) – Data Link Layer
a) (2 marks) Senders and receivers have agreed to use even parity. Acting as a sender, add
a parity bit to the following bit sequences.
b) (2 marks) Senders and receivers have agreed to use odd parity. Are the following
received bit sequences correct?
c) (3 marks) An ASCII transmission scheme uses DLE STX control characters to start a
frame and DLE ETX to end a frame. Using character stuffing (hint: only DLE needs to
be escaped), what are the ASCII sequences to transmit the following data streams?
AB DLE STX CD
ABC ETX DLE D ETX
d) (3 marks) A bit-oriented protocol uses the flag bits 01111110 to start and end the frame.
What will be the transmitted frames for the following streams of bits?
For all questions in this assignment not only content but also presentation will affect your mark.
You will lose marks if there are problems with the presentation, particularly with clarity. This
means that your answers to each question should be a coherent statement and that the spelling and
grammar of your submission will be taken into account in assessing its presentation.
For full marks, your answers should all be correct, clear, and coherent.
The standards of marking described in the unit outline L.O. 1 will be applied to this assignment as
relevant to the assignment topics.
In addition, the following particular standards will be applied in marking this assignment:
• Spelling and grammar:
o Assignment submissions with more than 4 spelling or grammatical errors will not
achieve a grade higher than distinction; submissions with more than 8 such errors
will not achieve a grade higher than credit.
o Ambiguous or poorly worded answers will receive a grade no more than a pass for
the individual question.
o Minor issues of clarity will receive a grade no more than credit for the individual
• Correctness of approach taken and answer obtained:
o Incorrect answers with the correct logic or approach will receive no more than a pass
for the individual question.
o Correct answers with incorrect logic or approach will receive no more than pass for
the individual question.
o Incorrect answers with no explanation of the approach taken or with the incorrect
approach will receive a fail grade for the individual question.
The questions will be marked individually, the marks totalled, and a final grade assigned that is no
more than indicated by the total marks, and no more than allowed by the standards specified
above and in the unit outline.
Submit on the iLearn page under ‘Assignments Section’. The submission is with a tool
called TurnItIn. This cross checks for online papers and other student papers for any
plagiarism (copying). In short – DON’T COPY – or get others to do your assignment, we
are pretty good at catching people out and the consequences can be severe. Do not trust
anyone who will take money to do assignments. They can take money from several
students, return the same assignment, and you get caught. They don’t care about you, but
Please do not include text of questions – TurnItIn reports this as copied text.