SIT202 Computer Networks Trimester 2 Assignment: Detailed Solutions

This document presents a comprehensive solution to a SIT202 Computer Networks assignment, addressing key concepts from the physical, data link, and network layers. The solution includes detailed answers to questions on bit rate calculation, multiplexing, and the differences between data rate and capacity. It also explores multiplexing and demultiplexing, circuit-switching, packet-switching, error detection and correction, and various wireless technologies. Furthermore, the solution covers topics such as media access control (MAC), wired and wireless LANs, and connecting devices. The assignment includes multiple-choice questions and problem-solving exercises, providing a thorough understanding of computer network principles. The solution is structured to align with the assignment brief's chapter-wise organization, ensuring a clear and concise presentation of the material. It also explores concepts related to the data link layer, including error detection, correction, and data link control protocols. The document provides a valuable resource for students studying computer networks, offering insights into various network protocols and technologies.

Running head: SIT202 COMPUTER NETWORKS TRIMESTER 2
SIT202 Computer Networks Trimester 2
Name of the Student
Name of the University
Author’s Note

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SIT202 COMPUTER NETWORKS TRIMESTER 2
Answer to Question 1 (Chapter 3)
1. What is the bit rate?
The processing and transfer speed rate of data is referred to as the bit rate and seconds is
used for measuring it. It can range from bps for the small values and reach to kbps or mbps. It is
also known as data rate. For digital telecommunication or networking the bit rate is measured in
second for the data passing through the communication network (Hayes, 2017). In case of
multimedia packets the bitrate is calculated as number of bits that are used per unit of playback
time. The encoding of the audio or video file affects the size of multimedia and its quality of
output
Thus, Bitrate = Amount of date / Time
2. If the number of signal level is 8 and the bandwidth is 3 MHz, what is the bit rate?
The calculation of bit rate is given below:
2 * 3 * log2(8) = 3 mbps
3. Suppose that the signal-to-noise ratio (SNR) is 6 dB. What is the capacity (in bits per second)
if the bandwidth is 3 MHz?
For the calculation of the capacity of the channel the following formula is used:
Signal to Noise Ration SNRdb = 10log10SNR
 SNR = 10SNRdb/10
 SNR = 10.6
 3.9810

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C = B log2 (1+SNR)
= 3*106 * log23.9810
= 3* 106 * 1.993
= 6 Mbps
4. Discuss the difference between the data rate and the capacity (e.g., answer why they are
different?)
The data rate and capacity differs from each other and the reason for its difference is give
below:
The rate of transferring data between the devices connected in the network represents the
data rate and the unit used for measuring the rate is mbps.
The maximum rate of transmission of data between the channels of communication is
known as the capacity. It differs from data rate because it has lower or upper limits of
transmission.
Answer to Question 2 (Chapter 6, 7, 8):
1. Explain the purposes of multiplexing and demultiplexing?
Multiplexing is used for combining the multiple data stream arriving from different
sources and transmitting it over a single data stream or channel. The multiplexing can be of two
types i.e. Time division multiplexing and frequency division multiplexing. A single channel non
overlapped time slots are used for the time division multiplexing and the data streams coming
from different sources are divided into equal sized units for interleaving it successively into the

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time slots (Ma et al., 2017). For the frequency division multiplexing simultaneous transmission is
used on the transmission medium by using different frequency band for each of the data streams.
The de multiplexing is done at the receiver end and it performs the reverse process
performed by the multiplexor. The de multiplexor receives the signals from the sender and
converts them in the original form for routing them as separated signals to the destination
address of the receivers.
2. Place one of “circuit-switching” and “packet-switching” into the followings sentences
• “Packet switching” can further be divided into two subcategories – virtual-circuit approach
and datagram approach.
• “Circuit-switching” takes places at the physical layer.
• In “Circuit-switching,” the resources need to be reserved during the setup phases.
3. Suppose that a packet is transmitted from Host A to Host B. The VIC of the packet at Host
A is “c”. What is VCI when the packet is arrived at Host B.

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SIT202 COMPUTER NETWORKS TRIMESTER 2
Incoming Interface Incoming VCI Outgoing Interface Outgoing VCI
2 c 1 d
Incoming Interface Incoming VCI Outgoing Interface Outgoing VCI
3 d 2 e
Incoming Interface Incoming VCI Outgoing Interface Outgoing VCI
0 f 1 g
Answer to Question 3 (Chapter 9, 10, 11):
1. Consider the parity-check code with 4-bit dataword
 What is the length of the codeword?
The 4 bit dataword parity check code has the length of 5.
 How many codewords the code has?
The parity check code has 2 code words
 What is the minimum Hamming distance?
The min. hamming distance for the parity check code (d) is 3.

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SIT202 COMPUTER NETWORKS TRIMESTER 2
 How many errors can be corrected?
d (min. hamming distance) is used for detection of d-1 error i.e. 2 errors.
2. In the following network, two hosts Alice and Bob are connected by three links and two
routers. There are two addresses (N: IP address and L: Link layer address) for each interface
of hosts and routers. Host Alice sends a datagram to host Bob. The datagram passes through
the routers and links to host Bob. Before sending, Alice makes a frame from the datagram,
then sends to the router-R1.
Explain how host Alice encapsulates the frame from the datagram, and then explain how
Router-R1 and Router-R2 prepare and forward those frames on link-2 and link-3 towards
host Bob. Mention how Alice gets R1’s link layer address, how routers get next destination
and link layer addresses in your explanation. Mention all link layer addresses (source and
destination) for all three frames in the links.

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SIT202 COMPUTER NETWORKS TRIMESTER 2
From the above figure it has been found that there are two routers and three links that
connects each of the hosts in the network and is the link between the sender Alice and receiver
Bob. Each of the hosts in the network has two types of address, one is the MAC address and
another is the IP address. For each of the link the router also has an IP address and unique
physical address and it has been found from the figure that for a single link 3 frames are there.
Each of the frame carries the same datagram and has similar source and destination address i.e.
N1 and N5. The link can have an effect on the changes in frame and from the above figure it has
been found that the L6 and L2 is the link layer address of the first link and L3 and L4 is the
address of the second link and L1 and L5 for the third link. The link address order and IP address
differs from each other since for IP address the source address comes first and for the link
address the source address comes after the destination address.
Answer to Question 4 (Chapter 12 - 17)
1. Choose “Yes” or “No” for each item?
Are there packet
collision?
Is carrier sensing
required?
Is the number of the
stations fixed?
TDMA No No No
Polling Yes Yes No
Slotted-ALOHA Yes Yes No
CSMA/CA Yes Yes No
2. Choose all wireless technologies in the followings.
• Bluetooth

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SIT202 COMPUTER NETWORKS TRIMESTER 2
• Gigabit ethernet
• 802.11n
• ADSL
• SONET
The wireless technology present above is as follows:
 Bluetooth
 802.11n
3. Choose “True” or “False” for each item?
True or False
In AMPS, CDMA has been used for channelization. False
Handoff is used in a cellular system to support continuous transmission for
a mobile station.
True
In CDMA-based cellular systems, the frequency-reuse factor can be 1. True
CSMA/CD is used for wireless LAN as it can avoid the hidden node
problem.
False

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SIT202 COMPUTER NETWORKS TRIMESTER 2
Bibliography
Gao, X., Edfors, O., Rusek, F., & Tufvesson, F. (2015). Massive MIMO performance evaluation
based on measured propagation data. IEEE Transactions on Wireless
Communications, 14(7), 3899-3911.
Hayes, J. E. (2017, August). Fiber optic network diagnostics for power, bit error rate and cable
plant problems. In Laser Beam Propagation in the Atmosphere (Vol. 10319, p. 1031903).
International Society for Optics and Photonics.
Ma, J., Karl, N. J., Bretin, S., Ducournau, G., & Mittleman, D. M. (2017). Frequency-division
multiplexer and demultiplexer for terahertz wireless links. Nature communications, 8(1),
729.
Saridis, G. M., Peng, S., Yan, Y., Aguado, A., Guo, B., Arslan, M., ... & Spadaro, S. (2016).
Lightness: A function-virtualizable software defined data center network with all-optical
circuit/packet switching. Journal of Lightwave Technology, 34(7), 1618-1627.