Question 1 (20 marks)
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)
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)
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
words]
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.
010
01100
011010
01100100
b) (2 marks) Senders and receivers have agreed to use odd parity. Are the following
received bit sequences correct?
1001
010101
0110110
011101101
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?
ABCD
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?
01010111000
01111110
00001110111110000111111111111110000
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