Develop and Analyze The performance of TCP connection when it is used for wireless networks You will find performance of TCP decreases dramatically when a TCP connection traverses a wireless link on which packets may be lost due to wireless transmission errors. This experiment is part of Visvesvaraya Technological University (VTU) syllabus for post graduate students

1. Lab Experiment – II.a
(per VTU M-Tech Syllabus)
On
Mobile Ad-Hoc Network
using
www.tetcos.com

2. Objective:
• Develop and Analyze
a) The performance of TCP connection when it is
used for wireless networks .You will find
performance of TCP decreases dramatically
when a TCP connection traverses a wireless link
on which packets may be lost due to wireless
transmission errors.

3. Introduction:
• Mobile Ad-Hoc Network (MANET) is a self-configuring network
of mobile nodes connected by wireless links to form an
arbitrary topology without the use of existing infrastructure.
The nodes are free to move randomly. Thus the network's
wireless topology may be unpredictable and may change
rapidly.
• In MANETs, random wireless errors and mobility serves as
primary contributor to losses as well as congestion. More than
80% of the losses in the network are due to link failures.
Essentially, most losses in ad-hoc networks occur as a result of
route failures
• TCP uses the occurrence of losses to detect congestion. If TCP
enters congestion control state because of packet losses
caused by random wireless errors and mobility, then the
throughput of TCP can be degraded significantly.

4. • TCP maintains a congestion window, which is an estimate of the
number of packets that can be in transit without causing congestion.
The congestion window starts at one packet, with new
acknowledgments causing it to be incremented by one, thus
doubling after each RTT. This is the slow start phase (exponential
increase). When a loss is detected by a timeout, slow start threshold
is then set to half the value of the congestion window, the
congestion window is reset to one packet, and the lost packet is
retransmitted.
• Subsequently, in the congestion avoidance phase (linear increase),
the congestion window is incremented by one packet per RTT. When
losses are detected by duplicate acknowledgments, indicating that
subsequent packets have been received, TCP retransmits the lost
packet, halves the congestion window, and restarts with the
congestion avoidance phase. The TCP assumption that all losses are
due to congestion becomes quite problematic over wireless links.
Multiple losses may repeatedly reduce the slow start threshold,
causing the slower congestion avoidance phase to take over
immediately, leading to large throughput degradations.

5. Performance metrics:
• Throughput: It is the rate of successfully transmitted
data packets in unit time in the network during the
simulation.

6. Performingthe experimentusing NetSim
(TCP Enabled)

7. Performingthe experimentusing NetSim
(TCP Disabled)

8. Results (IncreasingNodeDensity)
Throughput
Medium Properties Path Loss Exponent = 2
TCP Enabled Disabled
Throughput (Mbps) 0.732103 0.91431

9. Inference
• TCP uses the occurrence of losses to detect congestion. If TCP
enters congestion control state because of packet losses
caused by random wireless errors and mobility, then the
throughput of TCP can be degraded significantly.
• Hence you will find performance of TCP is lower when it is
enabled. This is because when a TCP connection traverses a
wireless link on which packets may be lost due to wireless
transmission errors.

10. NetSim is a premium simulation software, developed since 2003, with an
extensive and growing set of over 300 customers in over 15 countries.
NetSim is used for protocol modeling and simulation, network R & D and
defence applications. It allows users to analyze computer networks with
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