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Title: A Cross Layer Analysis of TCP Instability in Multihop Ad hoc Networks
Author: Hamadani, Ehsan Z.
ISNI:       0000 0001 3527 9695
Awarding Body: City University London
Current Institution: City, University of London
Date of Award: 2007
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Multihop ad hoc networks are collection of wireless nodes dynamically forming a temporary network without the use of any preexisting network infrastructure or centralized administration. Consequently, ad hoc networks and their \vireless links are fundamentally different from conventional stationary wireless and wired computer networks. In particular, incorporating the concept of TCPend-to-end congestion control for wireless networks is one of the primary concerns in designing ad hoc networks since TCP was primarily designed: and optimized· based on the assumptions for wired networks. In this thesis, out interest lies on tackling the TOP instability problem since due to the natureiof applications in multihop ad hoc networks (e.g. emergency operation and battlefield communication), connection instability or starvation even for a ~hort period of time can have a devastating impact on the Quality of Service and may not be acceptable for the end user. Through a detailed analysis and simulations, it is shown in this thesis that the main causes of TCP instability lie in three facto;s: overloading the network by sending more packets than the capacity of the channel, TCP sensitivity to out of order packets, and the channel access unfairness when multiple TCP connections are sharing the medium using 802.11 MAC protocoL To reduce TCP instability caused by excessive packet contention drops, a novel algorithm has been proposed that aims to reduce packet contention by optimizing the. amount of outstanding data in the network. To reduce TCP sensitivity to out of order packets, a new algorithm is proposed with the aim of performing more local recovery rather than end-to-end recovery. Finally, to address the TCPinstability caused by channel access unfairness, the 802.11 binary exponential backoff algorithm is replaced with a more conservative approach. In addition to addressing the problem of TCP instability, a 3-dimensional Markov model of 802.11 MAC is presented in this thesis to accurately analyze the 802.11 MAC throughput in ad hoc networks.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available