COIT20261 Network Routing and Switching Assignment 2: Term 1, 2018

This document provides a comprehensive solution to the COIT20261 Network Routing and Switching assignment. The assignment assesses understanding of routing concepts, including interpreting network diagrams, determining next-hop addresses, and completing routing tables. It also delves into IPv4 fragmentation, requiring calculations of fragment sizes and offsets, along with an analysis of the total packet size after fragmentation. Furthermore, the assignment explores TCP congestion control mechanisms, covering current techniques like TCP Reno and BBR, and analyzing the challenges in implementing new protocols. The solution includes detailed answers to all questions, demonstrating a strong grasp of networking principles and the ability to apply them to practical scenarios. The document also includes a Harvard referencing list.

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
Due date:
11:45pm AEST, Friday, Week 10
ASSESSMEN
T
Weighting: 25% 2
Objectives
This assessment task requires you to demonstrate your knowledge of routing concepts by
completing a number of exercise questions.
The questions are designed to help you to achieve the unit learning outcomes as listed in the
unit profile.
Instructions
You must do this assignment on your own – it is not a group assignment.
Thesequestions will require more time and effort than the first assignment so plan ahead and
start as early as possible. Question #3 may require additional research and analysisto
complete.
Type all your answers in the ‘Template for Your Answers’ Section of this document and
upload only that template. You can do that by copying the Template section into a new Word
document for uploading. Answers that are not typed into the “Template for Your Answers”
section may not be marked, or may be returned to you for re-typing and re-submission – late
penalties will apply.
Where instructed, you must show the steps you took to arrive at your answers. Write
your answers in your own words to avoid potential plagiarism and copyright violations.
You must submit the Answer section as a Word file (.doc or .docx). Do not submit PDF’s
or any other type of file without express permission from the Unit Coordinator.
Plagiarism Procedures can be found in the CQUniversity Policies section of the Unit Profile.
Assessment Requirements and Marking Criteria
There are 3 main questions each with sub-questions and the requirements are stated for each
one. You must answer all questions and their sub-questions. Marks are indicated in the
Answer Template.
The questions will be marked on correctness,logic and clarity, and addressing all parts of the
question.
The Assignment Questions begin on the next page.
REMEMBER, USE THE ANSWER TEMPLATE FOR ALL YOUR ANSWERS

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
Question 1 – Routing (10 marks)
Given the following network diagram, assume that all the networks shown are aware of each
other and have fully updated routing tables. Answer the questions that follow.
The questions (1 mark each except q.8):
1. From the point of view of router R4, what is the next-hop address for a packet
addressed to host 161.22.0.15/18?
2. From the point of view of router R1, which of its interfaces would it choose for a
packet being sent to network 161.22.0.0/18?
3. A host with an IP address of 200.11.60.36/24 has just sent a packet to a host with
address 150.32.0.240/18. How many hops is required between source and
destination?
4. A packet originating from network 220.10.40.0/24 arrives at router R1, however, R1
determines that the destination network is not in its routing table. What does R1 do
with the packet?
5. A packet arrives at router R2 with a destination address of 140.21.0.10/22. Which
interface port does R2 forward the packet out of?
6. A packet at router R3 has a destination address of 220.10.40.5/26. What next-hop
address would R3 use for this packet?
7. A packet is waiting at router R4 for forwarding. If the next-hop was a “direct
delivery”, which of these three networksis the destination network? 150.3.0.0/16, or
150.32.0.0/18, or 220.10.40.0/24?

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
8. Complete the information in the routing table for router R2 as shown in the Answer
Template for networks 150.3.0.0/16, 150.32.0.0/18, and the Default network. Show
the masks in longest mask order using CIDR format (3 marks).
Question 2 – Fragmentation in IPv4 (5 marks)
An IPdatagram5,400 bytes long with no options arrives at a router, which determines that the
next destination has an MTU of 1,500 bytes.Use the Answer Template to complete the
following questions, showing your calculations and reasoning.
a) Assuming that the router decides to fragment the packet into 4 fragments, determinea
correct size for each fragment, and identify the starting byte and ending byte of each
fragment(2.5 marks).
b) Calculate the fragmentation offset for each fragment(1.5 marks).
c) State whether the total number of bytes from all 4 fragments leaving the router will be
greater than the initial datagram size that arrived, or less than the initial datagram size,
and the reason(1 mark).
Question 3 – Congestion controls in TCP (10 marks)
This question affords you the opportunity to extend your thinking about congestion controls
in TCP beyond the textbook to observe what a real-world technology company, Google, is
doing in this space.
First, read this Network World article that reports on Google’s approach to improving
congestion controls in TCP:
https://www.networkworld.com/article/3218084/lan-wan/how-google-is-speeding-up-the-
internet.html?
idg_eid=f32fc7aec843db7ef67d0a4f08e3322d&email_SHA1_lc=&cid=nww_nlt_networkworld_daily_
news_alert_2017-08-22&utm_source=Sailthru&utm_medium=email&utm_campaign=NWW
%20Daily%20AM%20Alert%202017-08-22&utm_term=networkworld_daily_news_alert
You should also read the following more technical paper about it: https://tools.ietf.org/id/draft-
cardwell-iccrg-bbr-congestion-control-00.html
After reading both articles, answer the following questions:
1. Write a brief summary of the congestion controls currently available in TCP as
covered in this Unit (1 mark)
2. Identify and explain two problems with current congestion controls in TCP that are
pointed out in the articles (2 marks)
3. Summarize in your own words the difference(s) between the current TCP congestion
controls and Google’s new BBR protocol (3 marks)

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
4. The Network World article points out that it is difficult to get a new protocol accepted
as a global standard for TCP/IP. Why do you think this is the case? Give carefully
thought out reasons for your answer. (4 marks)
Important: for every direct quotation you use from these two sources or any other source, you
must immediately, after the quote, provideyourownexplanation of the quotation (for example,
explain why are you quoting it, how does it help answer the question, how does it support what you
are saying?) – marks will be deducted for failure to do so. In addition, correct referencing
conventions must be used throughout your work using the Harvard referencing convention. Your
answers will be marked on clarity, logic, relevance, use of own words and fully addressing all parts of
each question.
Remember that quotations alone will not be accepted as your explanation of the questions.
Quotations can support your explanations, but you must still provide the explanations yourself.
Best way forward is to keep direct quotations to a minimum, and use your own words.

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
TEMPLATE FOR YOUR ANSWERS
Type your answers in this section in the spaces provided. Spaces
can expand as you type.
First Name:_________________________ Last Name:____________________________
Student ID: __________________________
Question Number Mark
allocated
Marks
earned
Question 1: (10 marks)
1.
2.
3.
4.
5.
6.
7.
8.
150.3.0.2/16
161.22.0.1/18
5 hops
It broadcasts it to the entire network and waits for a reply from the
intended recipient to identify itself
150.3.0.4/16
150.3.0.0/16
150.3.0.0/16
q.8 Routing table of router R2:
Prefix Network address Next-hop address Interface
/16 150.3.0 150.3.0.0 150.3.0.4
/18 150.32.0 150.32.0.1 150.3.0.1
/16 150.3.0 150.3.0.0 150.3.0.1
150.3.0.2
150.3.0.3
1-7 1
mark
each, q.8
3 marks
Question 2: (5 marks)
a) Number of fragments = 5400/1500 = 3.6 = 4
Frame 1: starting byte=0; ending byte=1479
Frame 2: starting byte =1480; ending byte = 2959
Frame 3: starting byte= 2960; ending byte =4439
Frame 4: starting byte= 4440; ending byte= 5400
2.5
b) Frame 1 fragmentation offset = 0/8 = 0
Frame 2 fragmentation offset = 1480/8 =185
Frame 3 fragmentation offset= 2960/8 = 370
Frame 4 fragmentation offset= 4440/8 = 555
1.5

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
c)
The total number of bytes should be greater than the initial datagram size
because each frame arrives with a header of 20 bytes.
1
Question 3: (10 marks)
1.
TCP Reno
This congestion control technique implements the fast recovery algorithm
where the sender retransmits packets when it receives duplicate
acknowledgments before time out. This makes for faster retransmission. It
invokes the congestion avoidance algorithm without the need of going to
start slow mode to maintain reasonably consistent network performance
(Abed, Ismail, and Jumari, 2012).
TCP BBR
This is a model-based congestion control technique whose behaviour is
dictated by the network path that packet traffic flows through. It is based
on two basic parameters, the Bottleneck Bandwidth and the Round trip
propagation time (BBR) and determines the fastest way in which data can
be sent in the different routes (networkworld.com,2017).
Quick UDP connections (QUIC)
This is a congestion control technique developed by Google for low-
latency Internet transportation protocol over UDP. It utilises bandwidth
estimation to avoid congestion
Binary Increase Congestion control (BIC)
This is a loss based congestion control technique which reduces window
size when packet loss occurs. The window size is a linear function of
time.
CUBIC TCP
This is an improvement on BIC but less aggressive and TCP friendly. The
window size is a cubic function of time (Wang, Wen, Han, Zhang, J.,
Li, and Xiong, 2013).
Compound TCP
This is a delay based and loss based congestion control technique
developed by Microsoft Corporation to achieve bandwidth scalability and
TCP fairness (reduction of sending rate when congestion is detected).
1
2.
Shallow buffers-In loss based congestion control, when switches with
shallow buffers are used, packet loss occurs before congestion. This
triggers a multiplicative reduction of sent packets to unnecessarily low
levels
2

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
Deep buffers- In loss based congestion control, when bottleneck links
with deep buffers are used, delays occur because the congestion control
tries to fill up the buffers (bufferfloat).
3.
The BBR technique is proactive in its behaviour in that it first assesses the
network path and estimates the required bandwidth and the round trip
propagation time to determine the best route to use to send data. In
contrast, the TCP control methods were designed to slow down data
traffic once a congestion is detected. This makes BBR faster and more
reliable.
3
4. One of the main reasons why it is difficult to get a new protocol accepted
as a global standard for TCP/IP is because of the standardization issue.
The protocol has to be in line with the relevant international standards
bodies such as ISO and RFC for global implementation of the new
standard.
Another reason is that there are politics always involved in the
development and acceptance of these protocols. According to Larsen
(2012) both technical and political dynamics have shaped the TCP/IP
protocol since the 1970s. Within that span of time, many protocols have
been rejected by internet developers.
4
References
Abed, G.A., Ismail, M. and Jumari, K., 2012. Exploration and
evaluation of traditional TCP congestion control
techniques. Journal of King Saud University-Computer and
Information Sciences, 24(2), pp.145-155.
Cardwell, N., Cheng, Y., Yegane, S.H. & Jacobson, V., 2017,
BBR congestion control, Internet Congestion Control Research
Group
Larsen, R., 2012. The Political Nature of
TCP/IP. Momentum, 1(1), p.20.
Wang, J., Wen, J., Han, Y., Zhang, J., Li, C. and Xiong, Z.,
2013. CUBIC-FIT: a high performance and TCP CUBIC
friendly congestion control algorithm. IEEE Communications
Letters, 17(8), pp.1664-1667.
Networkworld, 2017, How Google is speeding up the Internet,
viewed 12 May 2018

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
<https://www.networkworld.com/article/3218084/lan-wan/
how-google-is-speeding-up-the-internet.html?
idg_eid=f32fc7aec843db7ef67d0a4f08e3322d&email_SHA1_l
c=&cid=nww_nlt_networkworld_daily_news_alert_2017-08-
22&utm_source=Sailthru&utm_medium=email&utm_campaig
n=NWW%20Daily%20AM%20Alert%202017-08-
22&utm_term=networkworld_daily_news_alert>
Total marks awarded 25 (max)
Less late penalties if applicable
Less plagiarism penalties if applicable
Total marks earned
Markers comments: