Network Routing and Switching Assignment: COIT20261, Term 2, 2019

This document presents a comprehensive solution to a network routing and switching assignment (COIT20261, Term 2, 2019). The assignment covers key concepts in network routing, including the creation and interpretation of routing tables for routers R1 and R4, detailing mask, network address, next-hop address, and interface configurations. It further explores the differences between classful and classless routing, with explanations on VLSM, CIDR, and packet forwarding mechanisms. The solution also delves into TCP congestion control techniques, such as congestion window (cwnd) and sliding window (rwnd), and the impact of shallow and deep buffers. Furthermore, the document compares current TCP congestion control mechanisms with BBR (Bottleneck Bandwidth and RTT) and discusses the challenges in standardizing congestion control schemes. This assignment provides a detailed understanding of network routing and switching principles.

COIT20261 Network Routing and Switching Term 2, 2019
Assignment item —Written Assessment-2
ANSWER TEMPLATE ASSIGNMENT TWO
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Questions Mark
allocated
Mark
earned
Question 1: (10 marks) 5 each
table
Answer: Routing table of router R1:
Mask Network address Next-hop address Interface
255.255.0.0 150.3.0.0 150.3.0.1 M0
255.255.19
2.0
150.32.0.0 150.32.0.1 M1
255.255.25
5.0
200.11.60.0 200.11.60.1 M1
255.255.25
2.0
140.21.0.0 140.21.0.1 M2
255.255.25
5.0
220.10.40.0 150.3.0.3 M0
255.255.19
2.0
161.22.0.0 150.3.0.3 M0
Routing table of router R4:
Mask Network address Next-hop address Interface
255.255.0.0 150.3.0.0 150.3.0.1 M0
255.255.19
2.0
150.32.0.0 150.32.0.1 M1
255.255.25
5.0
220.10.40.0 150.3.0.3 M0
5 max
5 max

COIT20261 Network Routing and Switching Term 2, 2019
Assignment item —Written Assessment-2
255.255.19
2.0
161.22.0.0 150.3.0.3 M0
255.255.25
5.0
200.11.60.0 200.11.60.1 M1
255.255.25
2.0
140.21.0.0 140.21.0.1 M2
Question 2: (5 marks)
a) Classful routing does not support VLSM and CIDR while classless
routing supports both CIDR, VLSM and FLSM. Hello messages are
used with classful routing in which an address is divided into three parts-
network, subnet and host. With classless routing, an address is divided
into two parts only-subnet and host.
1 max
b) Upon receiving a packet destined for 200.11.60.120, R3 checks its
routing table entry in order to determine the best path through which to
forward the packet. R3 has three directly connected routes-
220.10.40.0/24, 161.22.0.0/18 and 150.3.0.0/16. Now that there is no
route matching the destination, the router considers its remotely learnt
routes. This route is found to have been learnt through M0 (150.3.0.2)
through its M0 interface. The packet is then forwarded out of this
interface.
2 max
c) From R3, a packet whose destination address is 150.32.203.10 is
forwarded out through R3’s M0 interface. On this packet, an address
150.3.0.1 is added on the packet. On arriving at R4, it is then de-
encapsulated so that its address can be learnt. Upon finding the
destination address, the packet is further routed out of the network
through the M1 (150.32.0.1) R4’s interface.
2 max
Question 3: (10 marks)
1) TCP congestion control techniques help in the mitigation of congestion
or prevent it from occurring a network. Congestion window (cwnd) and
sliding window (rwnd) are used for this purpose. Rwnd is maintained by
a message recipient and is used in flow control. Cwnd on the other hand
is maintained by the sender for each session and represent the maximum
amount of data that can be sent over a link. Cwnd is initially set to
maximum segment size following successful synchronization between
two communicating devices and is gradually increased by one MSS in a
1 max

COIT20261 Network Routing and Switching Term 2, 2019
Assignment item —Written Assessment-2
phase called slow start. The lowest cwnd value is called ssthresh value.
2) Shallow buffers and deep buffers.
Shallow buffers happen before congestion has occurred in a network.
Long-based congestion control may lead to abysmal throughput
especially where switches with shallow buffers are used. Loss based
congestion control is difficult to achieve this way because of
overreaction and multiplicatively dynamically changing data rates
transfer.
In deep buffers, packet loss is experienced following traffic congestion.
This problem can lead to buffer float problems by repeatedly filling deep
buffers in last-mile links and causing needless delays while queueing
data packets.
2 max
3) Current TCP congestion controls are designed such that TCP revises
transmission rates downwards anytime it detects congestion in a
network. While this is achieved by way of monitoring a number of
packet losses in transport, at times the determination could be too late.
Additionally, the mechanism was efficient in traditional networks where
both switches and routers’ buffers matched to low-bandwidth network
links.
BBR does not wait for congestion to occur. It instead finds fastest way
of sending data across different routes and efficiently handles traffic
when traffic is congested. BBR estimates throughputs and roundtrips to
determine the time that each path is likely to use. \
BBR is compatible with alternative transport protocol.
3 max
4) Standardizing congestion control schemes in TCP networks is a critical
issue that requires critical consideration, discussion and time. BIC and
BBR came after one such a standard and only Google, or any other large
scale developer can push for faster standardization of TCP congestion
control.
4 max
Total marks awarded 25 (max)
Less late penalties
Less plagiarism penalties

COIT20261 Network Routing and Switching Term 2, 2019
Assignment item —Written Assessment-2
Total marks earned
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