ANALYSIS AND EXPERIMENTAL EVALUATION OF THE TRANSMISSION CONTROL PROTOCOL CONGESTION CONTROL ALGORITHMS IN A WIRELESS MULTIHOP ENVIRONMENT

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 10 Issue: 04 | Apr 2023 www.irjet.net p-ISSN: 2395-0072
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ANALYSIS AND EXPERIMENTAL EVALUATION OF THE TRANSMISSION
CONTROL PROTOCOL CONGESTION CONTROL ALGORITHMS IN A
WIRELESS MULTIHOP ENVIRONMENT
RAJAN S1, NANDHINI T2, RAMKUMAR D3, PUVIYA M4, KAVYA R5
1Professor, Dept. of ECE, Velalar College of Engineering and Technology, Thindal, Erode, Tamilnadu, India
. 2,3,4,5 B.E Final Year Students, Dept. of ECE, Velalar College of Engineering and Technology, Thindal, Erode,
Tamilnadu, India.
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Abstract - In today’s world wireless network plays a
major important role because of their characteristics such
as increased mobility, installation speed, reduced cost of
ownership, and wider reach of the network. Hence the
number of wireless network user increases which results in
high internet traffic. In order to avoid this kind of traffic on
the internet, Transmission control protocol (TCP) from the
transport layer of network architecture is used. TCP
provides various congestion control algorithms(TCP
variants). Each of them has different features but their main
objective is to provide maximum throughput. The purpose of
this paper is to analyze and experimentally evaluate TCP
variants such as TCP cubic, TCP hybla, TCP scalable, TCP
Vegas, and TCP Westwood for their throughput versus the
number of nodes. Therefore this analysis of TCP variants
provides a solid foundation for a robust TCP that can adapt
to a highly dynamic multi-hop wireless environment.
Key Words: Transmission Control Protocol (TCP),
congestion control, TCP Cubic, TCP Hybla, TCP Scalable,
TCP Vegas and TCP Westwood.
1. INTRODUCTION
Now days, demand for wireless communication system is
increasing. But it becomes difficult to maintain the data
rate because of multiple competing senders [14]. It may
lead to degradation of throughput in case of congestion
which is highly possible in wireless network. [16]
TCP congestion control algorithm from the transport layer
[4] is used to maintain high network utilization by
preventing network congestion. It is done by monitoring
the network for congestion and adjusts the data rate
accordingly. When TCP detects congestion, it reduces
transmission rate to prevent further congestion. Likewise
increases transmission rate when congestion subsides.
There are various kinds of TCP congestion control
algorithms [1] have been evaluated which is named as TCP
variants.
The performance of some of the selected TCP variants
such as TCP cubic, TCP hybla, TCP scalable, TCP vegas and
TCP westwood are analyzed and experimentally evaluated
[2]. It provides a strong foundation for creating robust TCP
that can adapt to highly dynamic multi-hop wireless
environment [5]. The simulation work is done on network
simulator 2. [3]
2. PROPOSED SYSTEM
The proposed system's flow diagram is shown in Figure 1
below
Figure 1: Flow Diagram of Proposed System
In this proposed system, analysis and experimental
evaluation of TCP variants [10] such as TCP cubic, TCP
hybla, TCP scalable, TCP vegas and TCP westwood is
presented. These variants are used to control congestion
in network traffic for wireless environment. All these TCP
variants can be differentiated using the metrics such as
throughput versus number of nodes. From this
comparative analysis [13] we can understand their
performance for multiple nodes in wireless environment.
We also examine their better performance for different

number of nodes which is used to provide strong
foundation for robust TCP that can adapt to dynamically
multihop wireless environment.
2.1 TCP congestion control algorithm
The Additive Increase Multiplicative Decrease (AIMD)
congestion control strategy is used by TCP. The
fundamental principle of AIMD is to gradually and steadily
raise the sending rate of packets until congestion is
identified. When congestion is identified it decreases the
sending rate of packets. AIMD functions as follows:
Additive increase: Initially, TCP starts with a low sending
rate and progressively raises it by gradually increasing the
sending rate by a little amount for each successful
transmission, until congestion is identified. Due to the
little addition it makes to the transmitting rate, this
increment is called as the additive increase.
Multiplicative Decrease: When congestion is found (for
instance, as a result of packet loss), TCP decreases the
sending rate by more than the current sending rate by
multiplying it by a factor less than 1. As it lowers the
transmission rate by a greater percentage, this reduction
is known as the multiplicative decrease.
Slow Start: When a new TCP connection is created, TCP
begins by transferring data at a low value of congestion
window(cwnd) to determine network’s available capacity
and then exponentially raises it until congestion is
detected. The congestion window is the maximum
numbers of bytes that can be transmit at any given time.
This initial phase of the AIMD algorithm is called the slow
start.
Congestion avoidance: once congestion window reaches a
certain threshold, sender then enters the congestion
avoidance phase. Here sender increases the congestion
window value linearly instead of exponentially. This
increase is very small to avoid causing congestion in
network.
Fast Retransmit/Fast recovery: If TCP detects a lost
transmission, it retransmits the packet without waiting for
a timeout (for instance, because of network congestion).
This technique, known as fast retransmit, lessens the delay
brought on by timeouts. In addition sender enters fast
recovery phase where the value of congestion window
halved from its current value and then enters congestion
avoidance mode.
Timeout: If no acknowledgement is received by the sender
for the transmitted packet for certain period of time, it
assumes packet has been lost and enters timeout phase.
Here congestion window value is reduced to one and slow
start phase gets restart. It ensures that sender is not
overwhelming the network with too much traffic.
Figure 2 Behaviour of TCP congestion control algorithm
2.2 TCP cubic
The performance of TCP on high-speed and long-distance
networks is improved by using TCP cubic. It is used to
estimate network’s available bandwidth and adaptively
adjusts the sending rate of data packets for better
utilization of network resources. It aims to increase the
sending data rate aggressively when the available
bandwidth is high, and reduces the sending rate more
conservatively when congestion is detected.
Cubic function [7] is used to determine the congestion
window size, where high amount of data may be
transferred as quickly as possible without having to wait
for a response from the receiver. The following is the
mathematical formula:
Cw = C(t − K)3 +Wmax
Where Cw is congestion window size, C is constant that
determines the rate of increase of the congestion window
size, k is constant that represents time at which congestion
window size was last reduced, Wmax is the maximum
window size allowed.
Starting with a small initial congestion window size, the
TCP Cubic algorithm gradually expands it until congestion
is noticed. When congestion is noticed, the size of the
congestion window is reduced, and the algorithm starts
again from the reduced size. The value of the constants C
and K are dynamically adjusted based on the network
conditions to optimize the performance of the algorithm.

Figure 3 TCP cubic congestion control.
The above Figure 3 shows the graphical representation of
TCP cubic congestion control[6].
2.3 TCP hybla
By optimizing the congestion window size based on
network conditions, TCP Hybla is used to enhance TCP
performance over high bandwidth and long latency
networks. By dynamically modifying the congestion
window size based on the current network conditions, it
seeks to shorten the time needed for TCP flows to
converge to a stable and fair bandwidth allocation.
The congestion window size is decreased to a low value at
the beginning of the TCP connection. Then it linearly
increases until the first congestion event is detected. When
congestion occurs, Congestion window size is halved from
its present level and size of the new congestion window is
calculated using hybla equation,
Where Cc is current congestion window size, Cn is new
congestion window size, α is a constant value between 0
and 1 that determines the weight of the new sample in the
calculation, bw is the estimated available bandwidth, rtt is
the estimated round trip time, ∆ is a constant value that
determines the rate of window increase.
Based on available bw and network’s rtt, this equation will
alter the congestion window size. It takes into account
both the current congestion window size and estimated
available bandwidth, and scales the increased rate based
on the estimated round trip time. It helps to avoid network
congestion while utilizing the available bandwidth
effectively.
The size of the congestion window is then raised linearly
until it experiences the occurrence of congestion. The
above steps were repeated for the duration of the TCP
connection.
2.4 TCP scalable
TCP scalable algorithm used to enhance the sender side of
standard TCP congestion control algorithm. By using the
traditional TCP it improves the performance such as high
speed and wide area networks. Using fixed increase and
decrease parameters, the congestion window in scalable
TCP can be modified. There are two phases to update the
congestion window in scalable TCP.
In slow start phase: Congestion window is raised by one
packet for each acknowledgement that is received.
In congestion avoidance phase: When no congestion has
been identified for at least one round trip time, then
window replies to each received acknowledgement with
the update.
Cw = Cw + α
Where Cw is a congestion window, α is constant parameter
between 0 and 1. In case if congestion occurs the
congestion window is multiplicatively decrease.
Cw = β.Cw
Where β is also a constant between 0 and 1. Typical values
for α=0.01 and β=0.875.
2.5 TCP vegas
TCP vegas[8] is used to decrease packet loss and improve
throughput. It provides more responsive and fair
congestion control compared to standard additive
increase and multiplicative decrease algorithm used by
TCP. RTT (Round Trip Time) is used here to measure the
state of the network.
By using the slow start mechanism, current congestion
window size is determined. Then actual and expected
throughput is calculated as follows.
when DIFF is less than the threshold value, then
congestion window increases exponentially. Vegas enters
the congestion avoidance phase when the DIFF exceeds
the threshold value as a result of the slow start phase's
queue building.

Figure 4 TCP vegas congestion avoidance.
The above Figure 4 shows the graphical representation of
TCP vegas congestion avoidance.
When there is congestion, Vegas[9] determines the
product of the DIFF and base RTT. A linear rise in cwnd
size occurs if the product is smaller than α. A linear drop in
cwnd occurs if the product is greater than β.
Otherwise, cwnd is maintained constant. If it receives a
duplicate ACK, it will resend the segment without waiting
for the three duplicate ACKs. As a result, segment loss is
noticed sooner.
2.6 TCP westwood
The TCP standard algorithm has been enhanced on the
sender side by TCP Westwood. It uses an alternative
method to estimate available bandwidth. TCP westwood
algorithm[11] initializes the congestion window (cwnd) to
maximum segment size (MSS), where MSS is the most
information that may be delivered in a single TCP
segment.
During slow start phase, TCP Westwood exponentially
raises the transmission rate. It uses adaptive slow start
mechanism that adjusts the rate of increase based on the
estimated available bandwidth. It helps to prevent
overshooting the available bandwidth and triggering
congestion control unnecessarily.
Once TCP westwood detects congestion, it switches to
congestion avoidance phase, where it reduces the sending
rate using a multiplicative decrease mechanism. Unlike
TCP reno it uses alternative method to estimate available
bandwidth called westwood+.
Westwood+ algorithm is used to estimate available
bandwidth on the network based on the rate of
acknowledge (ACK) packets. This provides feedback about
the actual throughput achieved by the sender, allowing
TCP Westwood to adjust the sending rate more precisely
and efficiently than other TCP variants. Based on the most
recent estimate of the available bandwidth, Westwood+
algorithm changes the transmission rate by calculating a
congestion window reduction factor.
TCP westwood uses the fast recovery mechanism to
recover from losses due to congestion. When TCP
Westwood is recovering, the congestion window is halved
and enters the state as "fast recovery". In this situation,
TCP Westwood retransmits dropped packets and still
sends new data, although very slowly. TCP Westwood
quits rapid recovery after successfully retransmitting all of
the lost packets and begins regular functioning.
3. RESULTS AND DISCUSSION
Table 1 simulation parameters
SIMULATION PARAMETERS
MAC IEEE 802.11
Routing protocol AOMDV
Propagation model shadowing
Simulation area 850m x 850m
Interface queue type Queue/DropTail/PriQueue
Queue length 50
Above table 1 shows the list of the simulation parameters.
Throughput values for TCP variants such as TCP cubic,
TCP hybla, TCP scalable, TCP vegas and TCP westwood has
been calculated for number of nodes using network
simulator 2[NS2].
The below table 2 shows the values for throughput versus
number of nodes.
Table 2 Throughput versus number of nodes.
THROUGHPUT
NUMBER OF NODES
50 100 150
cubic 80.27 1993.75 11001.3
vegas 48.87 1675.15 6907.18
westwood 127.1 2057.08 9867.12
scalable 190.61 1956.72 8281.22
hybla 64.28 1993.02 8700.02
This comparative analysis technique is used to determine
TCP performance in both crowded and scarce wireless
environments. The simulation uses nodes that range in
number from 50 to 150.

Chart -1: Graph between throughput versus number of
nodes
The above Figure 5 displays the image of graph between
throughput versus number of nodes. Throughput numbers
rise in proportion to the number of nodes.
From the graph, it shows with minimum number of nodes
scalable provides good throughput followed by westwood,
cubic, hybla and vegas. However, when the number of
nodes reaches upto 150, cubic provides good throughput
followed by westwood, hybla, scalable and vegas.
4. CONCLUSION
In this paper successful analysis and experimentation
evaluation of TCP congestion control algorithm has been
demonstrated. This analysis was conducted to investigate
how the congestion control algorithm behaves in a multi-
hop environment. Here we investigate among TCP cubic,
TCP hybla, TCP scalable, TCP vegas and TCP westwood in
which scalable provides good throughput in sparse
environment and cubic provides good throughput in dense
environment among the other variants.
The above analysis led to the following recommendations
is that the feedback mechanism should be added to the
standard queue to notify the sender.
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ANALYSIS AND EXPERIMENTAL EVALUATION OF THE TRANSMISSION CONTROL PROTOCOL CONGESTION CONTROL ALGORITHMS IN A WIRELESS MULTIHOP ENVIRONMENT

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