COIT20261 Network Routing and Switching (Term 1, 2018) Assessment

This document presents a comprehensive solution to a COIT20261 Network Routing and Switching assignment, focusing on key networking concepts. The assignment addresses three main questions. The first question examines routing principles, including next-hop addresses, interface selection, hop counts, and routing table completion, using a provided network diagram. The second question delves into IPv4 fragmentation, requiring calculations of fragment sizes, offsets, and an analysis of the total datagram size. The third question explores TCP congestion control, including a summary of existing mechanisms, an analysis of problems with current controls (shallow and deep buffers), a comparison of current TCP controls with Google's BBR protocol, and a discussion of the challenges in adopting new TCP/IP standards. The solution provides detailed answers, calculations, and explanations, referencing external sources and adhering to specified formatting requirements.

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.
These questions 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 analysis to
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 220.10.40.5/24. 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 networks is 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 IP datagram 5,400 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, determine a
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, provide your own explanation 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.
For the router R4 the next hop address for a data packet with destination
address to host 161.22.0.15/18 is 150.3.0.2.
For the Router R1 the interface selected for sending data packet to the
network 161.22.0.0 /18 is M2.
For the host with an IP address 200.11.60.36 /24 sending data packet to
the host with IP address 150.32.0.240 /18 requires minimum 2 hops to
reach the destination address.
For the data packet originated from the network 220.10.40.0 /24 arriving
at router R1 and if the destination address is not available in the routing
table the data packet is dropped.
When a data packet with destination address 140.21.0.10 /22 arrives at
router R2 the interface port used by the router for forwarding the data
packet is M0.
If the data packet at router R3 has a destination address 220.10.40.5 /26,
150.3.0.3 /16 is the next hop address used by the router R3 for sending the
data packet to the destination address.
For a data packet waiting at router R4 for being forwarded and if the next
hop address is a direct delivery the 150.30.0.0 16 is the destination
network address.
q.8 Routing table of router R2:
Prefix Network address Next-hop address Interface
255.255.255.0 220.10.40.0 150.3.0.3 M0
255.255.255.0 200.11.60.0 200.21.60.1 M1
255.255.252.0 140.21.0.0 140.21.0.1 M2
255.255.192.0 161.22.0.0 150.3.0.3 M0
255.255.192.0 150.32.0.0 150.3.0.1 M0
1-7 1
mark
each, q.8
3 marks

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
255.255.0.0 150.3.0.0 150.3.0.2 loopback
Question 2: (5 marks)
a) IP datagram = 5400 bytes
MTU = 1500 bytes
IP header = 20 bytes
Therefore, 5400 - 20 = 5380
MTU of 1500 bytes, 1500 - 20 = 1480 bytes of data is transmitted for
each of the data packets
Ceiling (5380 /1480) = 4 packets are required
1st packet: 20 bytes: IP header, 1480 bytes: Data ==
Correct size: 20 +1480 = 1500 bytes, starting byte :1 , ending bytes : 1480
2nd packet: 20 bytes: IP header, 1480 bytes: Data ==
Correct Size: 20 + 148 = 1500 bytes, starting bytes : 1481, ending bytes :
2960
3rd packet: 20 bytes: IP Header, 1480 bytes: data ==
Correct Size: 20 + 1480 = 1500 bytes, starting bytes: 2961, ending bytes:
4440
4th packet: 20 bytes: IP Header, 1345 bytes: Data ==
Correct size: 20 + 1345 = 1365 bytes, starting bytes: 4441, ending bytes:
5805
2.5
b) For the 1st packet:
Offset Value = 0
For the 2nd packet:
Offset Value = 185
For the 3rd packet:
Offset Value = 370
For the 4th packet:
Offset Value = 555
1.5
c)
For a data packet being sent in the network the IP header file consumes 20
bytes of data and it is similar for all the header files of the data packets.
The next datagram size is reduces to 20 bytes from the previous datagram
and for the given packet of 1500 bytes, 1481 is the starting byte of the
next packet because 20 bytes is considered as the header file length. Thus
the total number of byte from all the 4 fragments leaving the router would
be greater than the initial size of the datagram that have arrived.
1
Question 3: (10 marks)
1.
There are different congestion control mechanism available in TCP but
the unit covers the BBR algorithm such as RENO and CUBIC. It helps in
increasing the throughput of the network and reducing the bottleneck and
the congestion problem in the network. The delivery rate of the
connection should be measured by analysing the maximum bandwidth
available and minimum round-trip delay. The shallow and deep buffer can
be used for controlling the congestion while the BBR algorithm creates a
1

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
network path model for avoiding the congestion in the network.
2.
The two problems faced in the current congestion control in TCP that are
pointed in the article are given below:
Shallow Buffers: With the application of shallow buffers in case of loss
based congestion control the result can be abysmal as it overreacts and
due to its multiplicatively the sending rate of the data packet decreases. It
follows a dynamic approach and thus it is difficult for the utilization of
the loss based congestion.
Deep Buffers: The application of deep buffers can increase the delay by
repeatedly filling the buffers with the last mile link and creating a
needless queue in the network.
2
3.
The current TCP protocol differs from the BBR protocol created by
Google in different forms. The current TCP protocol creates a network
model with the available network paths for responding to the actual
congestion. In case of the algorithm developed by Google the speed of
sending the data traffic is optimized such that it goes not creates a clog on
the available routes on the network. The fastest path is analysed for
sending the data packets using different routes and the Googles algorithm
can handle the traffic for the congested routes. The throughput and the
roundtrip traffic for the multiple routes are constantly estimated and thus
the time taken by the data to traverse the network would be known and
the traffic is send at a speed that can be handled by the network.
3
4. There are different difficulty pointed out in the Network World article that
causes a barrier for the new protocol accepted as the global standard of
TCP/IP. The compatibility of the BBR algorithm with the other protocol
is tested by the IETF for standardizing it. It is not the first algorithm
developed for speeding the TCP there are different popular algorithm that
can be applied for controlling the congestion and standardizing is a long
term procedure that requires dozens of improvement. The Reno and the
CUBIC follows the same principle but the BBR additionally uses packet
timing and different figure to find the congestion in the route.
4
Total marks awarded 25 (max)
Less late penalties if applicable
Less plagiarism penalties if applicable
Total marks earned
Markers comments:

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
Bibliography
Bernstein, G., Lee, Y., Li, D., Imajuku, W. and Han, J., 2015. Routing and
wavelength assignment information encoding for wavelength switched optical
networks (No. RFC 7581).
Butler, B. (2018). How Google is speeding up the Internet . [online] Network
World. Available at:
https://www.networkworld.com/article/3218084/lan-wan/how-google-is-
speeding-up-the-internet.html?
idg_eid=f32fc7aec843db7ef67d0a4f08e3322d&email_SHA1_lc=&cid=nww_nl
t_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 [Accessed 15 May 2018].
Medhi, D. and Ramasamy, K., 2017. Network routing: algorithms, protocols,
and architectures. Morgan Kaufmann.
Tools.ietf.org. (2018). BBR Congestion Control. [online] Available at:
https://tools.ietf.org/id/draft-cardwell-iccrg-bbr-congestion-control-00.html
[Accessed 15 May 2018].