Network Routing and Congestion Control: A Comprehensive Analysis

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Question Number Mark
Allocated
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Earned
Question 1: (10 marks)
1.
2.
3.
4.
5.
6.
7.
8.
The next hop address is 150.3.0.3
It will use the m2 interface to send packet to 161.22.0.0/18
There will be two hops one is R4 with address 200.11.60.1 and second is
150.3.0.1 after that the packet will reach its destination.
When a packet arrives at the router R1 from network 220.10.40.0/24 the
router will check its routing table for the given destination address. Now
the network is not present in the routing table. The router will check the
default route in this case the default route is present at the next hop
150.3.0.4 of R2 router.
The router R2 will use the m0 interface to route the packet.
When a packet with destination address 220.10.40.5/26 arrives at router
R3 the router will use 115.3.0.3 as next hop address of R1 router.
In this case the destination network will be 150.3.0.0/16.
The routing table of the router R2:
Prefix Network address Next-hop address Interface
255.255.0.0 150.3.0.0 Directly
Connected
M0
255.255.192.0 150.32.0.0 150.3.0.1 M0
0.0.0.0 0.0.0.0 Directly
Connected
M1
1-7 1
mark
each, q.
8 3
marks
Question 2: (5 marks)
a) When the router receives the 5400 bytes long packet with no option. The
router will split the packet into four parts. It is because of the MTU allows
only 1500 bytes at a time.
The IP header takes 20 bytes header .So the size of each fragment are as
follows
- Packet 1 : 1480 bytes
- Packet 2 : 1480 bytes
- Packet 3 : 1480 bytes
- Packet 4 : 960 bytes
2.5
b
)
The calculation of Fragment Offset are as follow for each packet
Original IP Datagram
Sequence Identifier Total DF MF Fragment
1.5

Length My/Don’t Last/More Offset
0 1 5400 0 0 0
Fragment Offset value is calculated as a multiple of eight bytes so,
Fragment Offset for 2nd fragment will be 185 ( i.e.185x8 = 1480)
IP Fragment
Sequence Identifier Total
Length
DF
May/Don’t
MF Last /
More
Fragment
offset
0-0 1 1500 0 1 0
0-1 1 1500 0 1 185
0-3 1 1500 0 1 370
0-4 1 980 0 0 490
c) The total number of bytes from all the 4 fragments leaving the router will
be around 5480 and the original datagram size is 5400. The 4 fragment
size is bigger than the original datagram because of the 20bytes extra are
putting in each data fragment.
1
Question 3: (10 marks)
1. The current TCP protocol controls the network congestion in the network
device by sensing the loss of packets in the transmission. When it detects
it will tell the sender to slow down data transfer rate as it is not ready to
receive that much data at single time.
The network devices in middle will keep the buffer and process it
according to the receiver capacity of handling traffic.
1
2. Over the past few decades since the invention of the TCP/IP technology
may efforts has been done to speed up TCP protocols. Many of the
changes focused on monitoring the number of packets lost in the
transmission using the JACOBSON’s TCP Algorithm. Now it has two
biggest problem
- The AIMD (Additive Increase Multiplicative Decrease) algorithm
which is designed to monitor the number of packet it receives
continuously. And whenever the algorithm detects the loss of
packet it simply cuts the flow to half. It was good at that time
now the data demand has increased tremendously and sudden
cut in the flow disrupt the quality of service
- The algorithm doesn’t care about the packet and its priority. So
the network packets are dropped randomly which in the TCP
packet processing. It doesn’t provide fairness in the packet
selection
2
3. The current congestion control techniques is used for a very long time
and still used in the today’s network with some minor changes in the
original AIMD algorithm. So the google and the original inventor or the
congestion control has created a new algorithm called bottleneck
bandwidth and roundtrip So the main difference between the both
algorithm are given below as brief as possible.
- The current TCP congestion control protocol detect the number of
loss packet in the transmission and immediately drops the
3

network flow by 50% and whenever it sense less packet loss it
then again speed up the traffic processing. In the BBR, it
calculates the throughput and roundtrip traffic time across
various network routes. So it calculates how much time it will
take to traverse the network packet. So it will send the network
traffic at a speed that the network can handle it.
- The BBR is also compatible with an alternative transport protocol,
quick UDP connections (QUIC) which is also developed by the
google. The TCP Congestion control doesn’t support alternate
protocol to speed up the network performance.
- The BBR will not wait for a network congestion to occur. It works
on the modeling of how much data can fit in the network pipe. So
only the optimum amount of the network traffic will be send.
While the TCP congestion control waits for the packet to be loss
then it takes action. The optimum utilization of the network
bandwidth is not done
4. The network infrastructure and its underlying protocol are the backbone
of the today’s internet. Because the network traffic is transmitted over
this infrastructure which has been developed and updated several times
in the past decades. But most of the larger upgrades are done in the early
stages when the number of host machines is very less.
The network area is not so large and only institute and industries use the
network. But now the network has grown tremendously and the demand
for efficient network is always high. Now in order to changes and update
any of the protocol suits will require a large scale upgradation and it will
take a lot of time. Before accepting any new protocol as a standard all
over the world. These changes are checked and tested several times and
in various scenarios.
The TCP/IP Protocol suit is the global standard and the internet run on it.
So changing any rule and standard in the original protocol need to be
checked for 100% surety hat it will work according to the proposed design
and many times most of the application protocol failed to deliver what is
demanded. The TCP/IP Protocol is used worldwide and updating the
protocol will take a lot of effort. And most of the companies are not
intending to do that because it doesn’t stops the havoc created in
businesses which are running over it.
4
Total marks awarded 25 (max)
Less late penalties if applicable
Less plagiarism penalties if applicable
Total marks earned