Tcp Performance Optimization In Interaction With Mac Layer Over Multi-Hop Ad-Hoc Networks
Transport Control Protocol (TCP) has been designed to provide reliable data delivery between end hosts in traditional wired networks and is the most widely used reliable transport protocol over the internet. TCP keeps looking at the traffic inside the network by employing the congestion control m...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
2008
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| Online Access: | http://psasir.upm.edu.my/id/eprint/5378/1/FK_2008_23.pdf http://psasir.upm.edu.my/id/eprint/5378/ |
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| Summary: | Transport Control Protocol (TCP) has been designed to provide reliable data delivery
between end hosts in traditional wired networks and is the most widely used reliable
transport protocol over the internet. TCP keeps looking at the traffic inside the
network by employing the congestion control mechanisms. The basic assumption
underlying TCP congestion control is that packet losses are an indication of
congestion in the wired network. The effect of such an assumption on TCP's
performance in wireless environments has been a long-standing research study. The
reason is specific wireless properties such as high medium access contention; route
breakage and high bit error rate in radio channels pose different challenges in TCP
performance when it runs over wireless networks. In this thesis, the focus is given on
the interaction between TCP and Medium Access Control (MAC) layer in multi-hop
ad-hoc networks to deal with the effect of high medium access contention on TCP
throughput.
The main problem of TCP over IEEE 802.11 MAC protocol is the extensive number
of medium access carried out by TCP. In fact, TCP sender will be informed of successful transmissions by receiving the acknowledgment (ACK) from the other
end host to achieve the reliability. In this way, the MAC overhead may be caused by
generating redundant ACK packets that compete in the same route with data packets
for the media. As the load increases, the well-known hidden terminal effects caused
by interference between ACK and data packets can degrade TCP performance
dramatically if TCP acknowledges every incoming data packets.
To address above problem, in this thesis a dynamic TCP-MAC interaction strategy is
proposed which tries to reduce the number of induced ACKs by monitoring the
channel condition. To this end, the total collision probability collected along the path
from sender to receiver in MAC layer is used to properly set the number of the
delayed ACKs (DA) in TCP. Based on the measured collision probability, TCP sender
dynamically adjusts itself to the channel condition by delaying less ACKs in high
traffics and more in low traffic conditions. Upon this strategy, an enhanced TCP
throughput has been achieved in trade-off between moderate and high traffics. Finally,
the relationship between the TCP throughput and optimized number of delayed ACKs
has been investigated in different hop counts scenarios which employ a dynamic
traffic. The findings show that for a given hop count, there exists an optimized delay
window size which maximizes the TCP throughput. Overall, the achieved throughput
increments are up to about 30% over the regular TCP with DA extension and cwnd
limit and about 10% over the existing method called Dynamic Adaptive
Acknowledgment (TCP-DAA and TCP-DAAp). |
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