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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Power-aware routing in multi-hop wireless networks

Akhtar, Auon January 2013 (has links)
Wireless ad hoc networks (WAHNs) are a class of wireless networks that do no rely on a pre-existing infrastructure. Due to the infrastructure-less nature of WAHNs, the nodes themselves act as routers. A wireless mesh network (WMN) is a special type of WAHN that consists of a network of access points which are connected to each other through wireless links. While a WAHN is typically formed in an ad hoc manner, when the wireless devices come within communication range of each other, a WMN often has a more planned configuration. Compared to infrastructure-based networks, some of the advantages of WAHNs and WMNs include independence from central network administration, scalability, rapid deployment, last mile connectivity and cheaper network setup. Power consumption is an important design criteria in WAHNs and WMNs, least because it directly impacts the cost of network operation and maintenance. To add to this, the information and communication technology (ICT) industry is already being labeled as a substantial contributor to the total CO2 emissions on the planet. For this reason, green ICT has become a critical issue world wide. Since routing is one of the core functions of multihopnetworks like WAHNs and WMNs, significant research effort is being made to design energy-efficient and power saving routing algorithms. This thesis focuses on power-aware and energy-efficient routing in static WAHNs and WMNs that aim to extend network connectivity through multi-hop communication. Different transmission strategies are investigated for energy efficiency. These include point to point non-cooperative transmissions, distributed beamforming and centralized beamforming. Then, several power saving routing algorithms are proposed, each tailored for a specific type of transmission strategy. The proposed algorithms aim to minimize the end to end path power consumption while satisfying the signal to noise ratio requirements of the destination and the relay nodes. The performance of the proposed schemes is investigated thoroughly. Various figures of merit are used to highlight the efficiency of the proposed algorithms. These include end-to-end power consumption, total hop count, end-to-end delay and throughput. While most of the simulations are carried out in MATLAB, some packet level simulations are also conducted in OMNET++. The numerical and analytical investigations highlight the achievable energy saving gains.

A speculative execution approach to provide semantically aware contention management for concurrent systems

Sharp, Craig January 2013 (has links)
Most modern platforms offer ample potention for parallel execution of concurrent programs yet concurrency control is required to exploit parallelism while maintaining program correctness. Pessimistic con- currency control featuring blocking synchronization and mutual ex- clusion, has given way to transactional memory, which allows the composition of concurrent code in a manner more intuitive for the application programmer. An important component in any transactional memory technique however is the policy for resolving conflicts on shared data, commonly referred to as the contention management policy. In this thesis, a Universal Construction is described which provides contention management for software transactional memory. The technique differs from existing approaches given that multiple execution paths are explored speculatively and in parallel. In the resolution of conflicts by state space exploration, we demonstrate that both concur- rent conflicts and semantic conflicts can be solved, promoting multi- threaded program progression. We de ne a model of computation called Many Systems, which defines the execution of concurrent threads as a state space management problem. An implementation is then presented based on concepts from the model, and we extend the implementation to incorporate nested transactions. Results are provided which compare the performance of our approach with an established contention management policy, under varying degrees of concurrent and semantic conflicts. Finally, we provide performance results from a number of search strategies, when nested transactions are introduced.

Inferring malicious network events in commercial ISP networks using traffic summarisation

Sandford, Peter January 2012 (has links)
With the recent increases in bandwidth available to home users, traffic rates for commercial national networks have also been increasing rapidly. This presents a problem for any network monitoring tool as the traffic rate they are expected to monitor is rising on a monthly basis. Security within these networks is para- mount as they are now an accepted home of trade and commerce. Core networks have been demonstrably and repeatedly open to attack; these events have had significant material costs to high profile targets. Network monitoring is an important part of network security, providing in- formation about potential security breaches and in understanding their impact. Monitoring at high data rates is a significant problem; both in terms of processing the information at line rates, and in terms of presenting the relevant information to the appropriate persons or systems. This thesis suggests that the use of summary statistics, gathered over a num- ber of packets, is a sensible and effective way of coping with high data rates. A methodology for discovering which metrics are appropriate for classifying signi- ficant network events using statistical summaries is presented. It is shown that the statistical measures found with this methodology can be used effectively as a metric for defining periods of significant anomaly, and further classifying these anomalies as legitimate or otherwise. In a laboratory environment, these metrics were used to detect DoS traffic representing as little as 0.1% of the overall network traffic. The metrics discovered were then analysed to demonstrate that they are ap- propriate and rational metrics for the detection of network level anomalies. These metrics were shown to have distinctive characteristics during DoS by the analysis of live network observations taken during DoS events. This work was implemented and operated within a live system, at multiple sites within the core of a commercial ISP network. The statistical summaries are generated at city based points of presence and gathered centrally to allow for spacial and topological correlation of security events. The architecture chosen was shown to be exible in its application. The system was used to detect the level of VoIP traffic present on the network through the implementation of packet size distribution analysis in a multi-gigabit environment. It was also used to detect unsolicited SMTP generators injecting messages into the core. ii Monitoring in a commercial network environment is subject to data protec- tion legislation. Accordingly the system presented processed only network and transport layer headers, all other data being discarded at the capture interface. The system described in this thesis was operational for a period of 6 months, during which a set of over 140 network anomalies, both malicious and benign were observed over a range of localities. The system design, example anomalies and metric analysis form the majority of this thesis.

Using self-reported social networks to improve opportunistic networking

Bigwood, Greg January 2012 (has links)
Opportunistic networks provide an ad hoc communication medium without the need for an infrastructure network, by leveraging human encounters and mobile devices. Routing protocols in opportunistic networks frequently rely upon encounter histories to build up meaningful data to use for informed routing decisions. This thesis shows that it is possible to use pre-existing social-network information to improve existing opportunistic routing protocols, and that these self-reported social networks have a particular benefit when used to bootstrap an opportunistic routing protocol. Frequently, opportunistic routing protocols require users to relay messages on behalf of one another: an act that incurs a cost to the relaying node. Nodes may wish to avoid this forwarding cost by not relaying messages. Opportunistic networks need to incentivise participation and discourage the selfish behaviour. This thesis further presents an incentive mechanism that uses self-reported social networks to construct and maintain reputation and trust relationships between participants, and demonstrates its superior performance over existing incentive mechanisms.

Dynamic service deployment through consensus negotiation in programmable ad hoc networks

Prince, Daniel David Campbell January 2004 (has links)
No description available.

A language and architecture for unifying system-on-chip design

Watt, Douglas Ramsay January 2004 (has links)
No description available.

The explanation of benefits afforded by the application of force feedback effects to pointing interactions

Bierton, Robert A. January 2007 (has links)
No description available.

Quality of service management in IP networks

Awotula, Titus January 2006 (has links)
No description available.

Fixed broadband wireless access systems at millimeter wave frequency

Zhang, Jin January 2007 (has links)
No description available.

Resource allocation in networks with dynamic topology

Usaha, Wipawee January 2004 (has links)
No description available.

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