Term 1, 2018: COIT20261 Network Routing and Switching Assignment

This document presents a complete solution to a written assessment on network routing and switching (COIT20261), covering key concepts such as routing tables, IP datagram fragmentation, and TCP congestion control mechanisms. The assignment includes multiple-choice questions related to routing table lookups and next-hop address determination, as well as a detailed analysis of IP datagram fragmentation, calculating packet sizes, offsets, and the number of packets required. Furthermore, the solution explores congestion control mechanisms like Reno, CUBIC, and the BBR algorithm, discussing the role of network buffers, round trip time, and bandwidth in optimizing data packet delivery. The assignment also references external resources, including IETF drafts and Network World articles, to provide a comprehensive understanding of the subject matter.

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
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 150.3.0.2 is the next hop address for the packet
addresses to host 161.22.0.15/18
For the router R1 the interface used for sending the data to the network
161.22.0.0/18 is M2.
When a packet is sent between 200.11.60.36 /24 and 150.32.0.240 /18 a
minimum 2 hops needs to be travelled for reaching the destination
location.
If a data packet generated from the source 200.11.60.36 /24 reaches the
router R1 and the router does not finds the destination address in the
routing table it drops the data packet.
If a data packet with the destination address 140.21.0.10/22 reaches the
router R2 the interface M0 is used for forwarding the data packet.
The destination address of a packet at router R3 is 220.10.40.5 /24 the
next hop address for sending the data packet would be 150.3.0.3 /16
For the data packet waiting on the router R4 and if the next hop is a direct
delivery the network 150.3.0.0 /16 is the destination network.
q.8 Routing table of router R2:
Prefix Network
address
Next-hop
address
Interfac
e
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
1-7 1
mark
each, q.8
3 marks

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
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
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) Offset value of the 1st packet fragmentation = 0
Offset value of the 2nd packet fragmentation = 185
1.5

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
Offset value of the 3rd packet fragmentation = 370
Offset value of the 4th packet fragmentation = 555
c) 20 bytes is consumed by the header byte of the data packet and it is same
for all the data packets transferred in then network. If the total size of the
datagram packet is 1500 the starting byte of the second packet is 1480
byte and thus the total byte sent is less than the initial size of the datagram
that arrives in the router.
1
Question 3: (10 marks)
1. Reno and CUBIC are the two different clog control mechanism that are
used in TCP and it is covered in the unit. The unit also describes about the
current BBR algorithm developed by Google for speeding up the internet
and optimizing the rate of delivery of the data packets in the current
network using the TCP clog control mechanism. For the optimization of
the delivery of the data packets it is important to identify the round trip
time and the bandwidth and sending the data packets at a rate that does
not causes congestion in the network. For avoiding the bottleneck
situation different buffers are used and a network model is created for the
selection of the best path in the network.
1
2. The application of the buffer in the network can increase the delay for
sending and receiving the data packets with the formation of unnecessary
queue in the network. The application of the shallow buffers in the loss
based congestion network can impact the network as it can decrease the
sending rate of the data packet. The application of the deep buffer can
generate an unnecessary que as it is repeatedly filled with the last mile
link of the network.
2
3. The BBR and the TCP protocol are used for controlling the congestion in
the network using the TCP/IP protocol but both follows different
mechanism for controlling the loss and the congestion. The BBR
algorithm utilizes an optimized speed for sending the packets by creating
a network model and finding the best path and calculating the round trip
time. The path is selected and the data packets are sent at a rate that would
not cause congestion. The constant calculation of the throughput and the
round trip time would help to estimate the time required for successfully
deliver a data packet in the network and control the rate of sending the
data packet in the network.
3
4. The Network World Article highlights different difficulty which acts as a
barrier for accepting the new BBR algorithm developed by Google as a
standard TCP protocol. A test should be made on the newly developed
4

COIT20261 Network Routing and Switching (Term 1, 2018)
Assignment item —Written Assessment-2
protocol before accepting it as a global standard and IETF is responsible
for testing the protocol against different conditions such as analysis of its
compatibility against the other popular algorithm for controlling the
congestion and increasing the efficiency of the TCP protocol. There are
different other protocol that also uses the same principle as the BBR
algorithm and they are also not standardized since there are many
improvements can be made in the protocols for eliminating the bottleneck
condition in the network and reducing the clogs.
Total marks awarded 25 (max)
Less late penalties if applicable
Less plagiarism penalties if applicable
Total marks earned
Markers comments