SIT202 Computer Networks Trimester 2, 2020 Problem Based Learning Task 1
Due Date: 8pm Sunday August 30th, 2020
This assessment is marked out of 100 marks and is worth 35% of your final unit mark.
All work completed/submitted as part of this assessment task must be your own, individual work. Any content drawn from other materials, including unit materials, must be clearly quoted where appropriate, and/or clearly referenced. All students should review and be familiar with the content provided by the University regarding how to reference other materials:
https://www.deakin.edu.au/students/studying/study-support/referencing
And in particular the information provided regarding Academy Integrity:
https://www.deakin.edu.au/students/studying/academic-integrity
Use of Illustrations
Note that several questions below may require you to include an illustration in your answer. This must be your own illustration, not a graphic copied from the Internet or any other source (textbook, class slides, etc.). Illustrations from the Internet (whether directly copied or reproduced by you) will not be awarded any marks.
There are many illustration programs that you may use for this purpose, including several free applications accessible via the Web. If you are unable to use these programs however, you may include a scanned/photographed hand-drawn illustration in as long as that illustration is clearly legible.
HD Tasks
Note that there are one or more ¡°HD Tasks¡± identified in the requirements below. These tasks are more difficult to answer and total 20% of the marks available for this assessment. A HD result reflects achievement in the unit of a deep understanding of the unit content and ability to extend your knowledge beyond that covered in the unit directly. You can expect these tasks will be assessed harder than other tasks reflecting demonstration of this level of achievement.
This assessment task must be completed individually,
group work and/or collaboration with other students is prohibited.
Question 1 / Week 1 (4 + 6 + 6 + 8 = 24 marks) Computer networks are constructed using a modular architecture known as layering.
a) Explain how layering simplifies the protocols used in networks and intermediary devices.
b) Explain how encapsulation and decapsulation works and how these mechanisms are used
to achieve logical communication between peer layers.
c) A key advantage of layering is that a protocol in one layer can be replaced with another
with little or no impact. Discuss how this works, including any influence/expectations on
adjacent layers (layers above/below where the protocol is replaced).
d) (HD Task) Consider a home network where a computer connected via Ethernet to the
router is printing to a printer that is connected by Wi-Fi to the same router using the Internet Printing Protocol (IPP). Assuming that the Wi-Fi network is just an extension of the existing wired LAN, i.e., they are the same subnet, illustrate the communication protocol stacks of all devices in the communication path, indicating both the layer name and actual protocol (see Week 1 Slide #32 for an example without the actual protocols named).
Question 2 / Week 2 (15 marks)
Consider the differences between datagram switching and virtual-circuit switching networks. Explain how the following aspects of communication are impacted (or why they are not impacted) by these different switching techniques:
i. Delays encountered by data travelling from sender to receiver;
ii. The order packets would arrive at the receiver; and
iii. The reliability of packets being delivered to the receiver.
Question 3 / Week 3
Given the following network topology:
(10 + 13 = 23 marks)
a) Illustrate the use of network layer addresses and link-layer addresses as a packet is sent from the PC on the left to the PC on the right.
b) Explain what is happening in your illustration, including why some addresses are changing and others not, where encapsulation/decapsulation is occurring and at what layers.
Question 4 / Week 4 (10 + 7 = 17 marks)
a) Modern Ethernet networks make use of switches which, when only one device is connected to a switch port, enables CSMA/CD to be disabled and full-duplex communication to be used instead. Explain why this same technique is not possible for WiFi networks, which require use of CSMA/CA.
b) (HD Task) The CSMA/CA protocol, used in WiFi networks is able to reduce the likelihood of collisions occurring, but is unable to eliminate them. Given that the RTS/CTS flow control mechanism ensures only one device transmits at any one time, explain why collisions can still occur. In your answer, use a scenario/example to aid in your explanation (an illustration may work well for this).
Note: assume that only one WiFi network is in use and there are no other devices are using the same frequencies.
Question 5 / Week 5 (8 + 8 + 5 = 21 marks)
The IP protocol includes error control in the form of a checksum that validates only the content of the IP header. As noted in the Week 5 slides, this design decision was based on the inefficiency of providing error control at the network layer once fragmentation had been considered.
a) Draw an illustration that shows a packet arriving at a router, which is then fragmented into two or more fragments for transmission to the receiver. Indicate any relevant IP header fields in your illustration.
b) Explain why fragmentation may occur and how it works (both fragmentation and reconstruction at the destination).
c) (HD Task) Explain why the presence of fragmentation would influence the decision to validate only the IP header instead of the entire datagram.