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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.
1

Camel; an adaptive migratory applications framework

Al Bar, A. M. January 2004 (has links)
Process Migration techniques have been around since the early days of Networked Operating Systems. However, process migration has not been widely adopted in software architecture design due to performance cost and unfeasible applications domain at that time. The emergence of new mobile computing technology is now the driving force to investigate new migration models that will support mobile applications and will help to optimise the available scarce resources that are a feature of the mobile computing environment. New alternatives to process migration have been developed and are attracting more researchers. These alternatives include remote execution, process cloning, mobile agents, and mobile code systems. They are simpler to implement and more inexpensive in their overhead cost to the execution environment. This thesis investigates the design and a reference implementation of a framework to support application designers in building adaptive migratory applications. The framework is called Camel. For applications to migrate they need to capture/save their states so that they can be restarted at the new location. However, capturing/saving mechanism of low level execution state imposes great performance cost on applications and are not necessarily required for migration. In Camel we argue that applications can migrate successfully with no need for low level execution state and with minimum application state, if the application designer decides on the necessary state at design time. The design of adaptive migratory applications requires infrastructure support for monitoring the execution environment so that applications can be notified of any changes in a critical resource that might trigger migration, adaptation or a combination of both. Monitoring a critical resource is accomplished through the use of the monitor component of Camel. In this work we only focus on monitoring of memory and application throughput. The framework provides support for the application designer to construct adaptation at design time through the provision of a common framework of helper objects and classes. The designer can then tweak the behaviour of the application through a set of policy profiles to better utilise critical resources
2

Integrated ZigBee RFID sensor networks for resource tracking and monitoring in logistics management

Yang, Huanjia January 2010 (has links)
The Radio Frequency Identification (RFID), which includes passive and active systems and is the hottest Auto-ID technology nowadays, and the wireless sensor network (WSN), which is one of the focusing topics on monitoring and control, are two fast-growing technologies that have shown great potential in future logistics management applications. However, an information system for logistics applications is always expected to answer four questions: Who, What, When and Where (4Ws), and neither of the two technologies is able to provide complete information for all of them. WSN aims to provide environment monitoring and control regarded as When and What , while RFID focuses on automatic identification of various objects and provides Who (ID). Most people usually think RFID can provide Where at all the time. But what normal passive RFID does is to tell us where an object was the last time it went through a reader, and normal active RFID only tells whether an object is presenting on site. This could sometimes be insufficient for certain applications that require more accurate location awareness, for which a system with real-time localization (RTLS), which is an extended concept of RFID, will be necessary to answer Where constantly. As WSN and various RFID technologies provide information for different but complementary parts of the 4Ws, a hybrid system that gives a complete answer by combining all of them could be promising in future logistics management applications. Unfortunately, in the last decade those technologies have been emerging and developing independently, with little research been done in how they could be integrated. This thesis aims to develop a framework for the network level architecture design of such hybrid system for on-site resource management applications in logistics centres. The various architectures proposed in this thesis are designed to address different levels of requirements in the hierarchy of needs, from single integration to hybrid system with real-time localization. The contribution of this thesis consists of six parts. Firstly, two new concepts, Reader as a sensor and Tag as a sensor , which lead to RAS and TAS architectures respectively, for single integrations of RFID and WSN in various scenarios with existing systems; Secondly, a integrated ZigBee RFID Sensor Network Architecture for hybrid integration; Thirdly, a connectionless inventory tracking architecture (CITA) and its battery consumption model adding location awareness for inventory tracking in Hybrid ZigBee RFID Sensor Networks; Fourthly, a connectionless stochastic reference beacon architecture (COSBA) adding location awareness for high mobility target tracking in Hybrid ZigBee RFID Sensor Networks; Fifthly, improving connectionless stochastic beacon transmission performance with two proposed beacon transmission models, the Fully Stochastic Reference Beacon (FSRB) model and the Time Slot Based Stochastic Reference Beacon (TSSRB) model; Sixthly, case study of the proposed frameworks in Humanitarian Logistics Centres (HLCs). The research in this thesis is based on ZigBee/IEEE802.15.4, which is currently the most widely used WSN technology. The proposed architectures are demonstrated through hardware implementation and lab tests, as well as mathematic derivation and Matlab simulations for their corresponding performance models. All the tests and simulations of my designs have verified feasibility and features of our designs compared with the traditional systems.
3

A tool for collaborative online dialogue : CodeZebraOS

Diamond, Sara January 2009 (has links)
How can an artist-created conversation and data visualisation tool be of value to the practices of data visualisation and social media? In what ways can the processes of designing and analysing such a tool inform the fields of Digital Media Studies, Data Visualisation, Collaboration Studies and Design Methods Research? The primary research was the creation of a unique conversation visualisation tool that encourages creativity in new ways. CodeZebraOS facilitates brainstorming, lateral thought, creative sketching, and the analysis of social dynamics and emotions in online conversation. This thesis integrates dialogues from Digital Media Studies and Collaboration Studies into the field of Data Visualisation. CodeZebraOS contributes a unique metaphor to Data Visualisation, advocating aesthetics that account for relationships between biological, human and virtual worlds, keeping in mind the structure of the source data. CodeZebraOS contributes to current understandings of the complex relationships between human and zoological life forms in Science and Technology disciplines, and applies the study of these relationships to the practice-based design of the tool's aesthetics. A major contribution is the CodeZebra Method, a unique process created for interdisciplinary teams who undertake software development. The methods used to develop CodeZebraOS derive from the empirical approaches of the charrette, participatory design, agile computing and artistic improvisation, creating a hybrid development method. This approach employed usability testing and public deployment at every stage of the tool's development, concluding with a self-reflexive analysis of the artistic and technological results. Finally, this thesis emphasises the skills and theoretical understandings of artists and designers. This thesis argues for the centrality of both the artist's and the designer's role in the creation of social media and data visualisation tools. It makes an original and substantial contribution in four forms: the creation of CodeZebraOS itself; a substantial academic dissertation with an interdisciplinary analysis of practice in the theoretical context of Computer Science (Data Visualisation), Digital Media Studies (ArtSci), Design Methods Research, and Collaboration Studies; the creation and explication of the CodeZebra Method, and finally, a demonstration of the primacy of art and design skills in software development
4

Improving the performance and reliability of systems which employ the 'Controller Area Network' protocol through low-level changes to the controller implementation

Sheikh, Imran January 2011 (has links)
The CAN (Controller Area Network) protocol provides one of the cost-effective methods to network current generations of distributed embedded systems. Although it is a robust protocol with short messages and simple priorities, it is largely thought of as only being suitable for soft real-time, event-triggered systems. Safety critical applications require highly predictable behaviour with strict bounds on worst-case message transmission times; the next-generation mechatronic systems also requires a high level of information throughput. In its current form, CAN lacks most of these requirements principally due to its medium access scheme and physical-layer design. This thesis presents a frame work which aims to enhance the capabilities of CAN, in order to push the boundaries of the protocol’s current operation. In particular, the main research question to be addressed is the exploration of the extent to which low-level modifications can enhance CAN suitability for use in the next generation of critical systems. In order to answer this question, it is first necessary to develop a flexible and robust platform to implement these modifications using a novel facility made up from custom soft-core CAN controllers. This novel facility was then employed to implement and experimentally investigate three small but conceptually significant protocol modifications as follows: Increasing the effective data rate from 1 to 10 Mbps whilst doubling the effective payload from 8 to 16 bytes; Reduction of unwanted transmission jitter by compensating for bit stuffing; Enabling a windowed transmission scheme to provide optimal trade-off’s between transmission reliability and real-time behaviour in noisy environments. The thesis describes the results obtained from these experiments and summarizes the main pros and cons that appear. The thesis then concludes with observation that the modified CAN protocol may be suitable for use with certain classes, of the next generation time-critical distributed embedded systems.
5

Interconnection networks for parallel and distributed computing

Xiang, Yonghong January 2008 (has links)
Parallel computers are generally either shared-memory machines or distributed- memory machines. There are currently technological limitations on shared-memory architectures and so parallel computers utilizing a large number of processors tend tube distributed-memory machines. We are concerned solely with distributed-memory multiprocessors. In such machines, the dominant factor inhibiting faster global computations is inter-processor communication. Communication is dependent upon the topology of the interconnection network, the routing mechanism, the flow control policy, and the method of switching. We are concerned with issues relating to the topology of the interconnection network. The choice of how we connect processors in a distributed-memory multiprocessor is a fundamental design decision. There are numerous, often conflicting, considerations to bear in mind. However, there does not exist an interconnection network that is optimal on all counts and trade-offs have to be made. A multitude of interconnection networks have been proposed with each of these networks having some good (topological) properties and some not so good. Existing noteworthy networks include trees, fat-trees, meshes, cube-connected cycles, butterflies, Möbius cubes, hypercubes, augmented cubes, k-ary n-cubes, twisted cubes, n-star graphs, (n, k)-star graphs, alternating group graphs, de Bruijn networks, and bubble-sort graphs, to name but a few. We will mainly focus on k-ary n-cubes and (n, k)-star graphs in this thesis. Meanwhile, we propose a new interconnection network called augmented k-ary n- cubes. The following results are given in the thesis.1. Let k ≥ 4 be even and let n ≥ 2. Consider a faulty k-ary n-cube Q(^k_n) in which the number of node faults f(_n) and the number of link faults f(_e) are such that f(_n) + f(_e) ≤ 2n - 2. We prove that given any two healthy nodes s and e of Q(^k_n), there is a path from s to e of length at least k(^n) - 2f(_n) - 1 (resp. k(^n) - 2f(_n) - 2) if the nodes s and e have different (resp. the same) parities (the parity of a node Q(^k_n) in is the sum modulo 2 of the elements in the n-tuple over 0, 1, ∙∙∙ , k - 1 representing the node). Our result is optimal in the sense that there are pairs of nodes and fault configurations for which these bounds cannot be improved, and it answers questions recently posed by Yang, Tan and Hsu, and by Fu. Furthermore, we extend known results, obtained by Kim and Park, for the case when n = 2.2. We give precise solutions to problems posed by Wang, An, Pan, Wang and Qu and by Hsieh, Lin and Huang. In particular, we show that Q(^k_n) is bi-panconnected and edge-bipancyclic, when k ≥ 3 and n ≥ 2, and we also show that when k is odd, Q(^k_n) is m-panconnected, for m = (^n(k - 1) + 2k - 6’ / ‘_2), and (k -1) pancyclic (these bounds are optimal). We introduce a path-shortening technique, called progressive shortening, and strengthen existing results, showing that when paths are formed using progressive shortening then these paths can be efficiently constructed and used to solve a problem relating to the distributed simulation of linear arrays and cycles in a parallel machine whose interconnection network is Q(^k_n) even in the presence of a faulty processor.3. We define an interconnection network AQ(^k_n) which we call the augmented k-ary n-cube by extending a k-ary n-cube in a manner analogous to the existing extension of an n-dimensional hypercube to an n-dimensional augmented cube. We prove that the augmented k-ary n-cube Q(^k_n) has a number of attractive properties (in the context of parallel computing). For example, we show that the augmented k-ary n-cube Q(^k_n) - is a Cayley graph (and so is vertex-symmetric); has connectivity 4n - 2, and is such that we can build a set of 4n - 2 mutually disjoint paths joining any two distinct vertices so that the path of maximal length has length at most max{{n- l)k- (n-2), k + 7}; has diameter [(^k) / (_3)] + [(^k - 1) /( _3)], when n = 2; and has diameter at most (^k) / (_4) (n+ 1), for n ≥ 3 and k even, and at most [(^k)/ (_4) (n + 1) + (^n) / (_4), for n ^, for n ≥ 3 and k odd.4. We present an algorithm which given a source node and a set of n - 1 target nodes in the (n, k)-star graph S(_n,k) where all nodes are distinct, builds a collection of n - 1 node-disjoint paths, one from each target node to the source. The collection of paths output from the algorithm is such that each path has length at most 6k - 7, and the algorithm has time complexity O(k(^3)n(^4)).
6

Improvement of High Rate Wireless Personal Area Network Protocol (IEEE 802.15.3)

Sulaiman, Thafer January 2008 (has links)
The IEEE 802.15.3 is a High Rate (HR) Wireless Personal Area Network (WPAN) standard, which is standardised by IEEE in 2003. This standard is· MACIPHY specifications for wireless connections ofpersonal devices. This thesis proposes enhancements for the HR WPAN standard including the Piconet Coordinator (PNC) selection criteria and power management. The following topics have been studied, analysed, simulated and presented in this thesis: 1. Piconet Coordinator Selection Criteria 2. User Centricity in WPAN using the Personal Identification Device (PID) 3. User Detection (using the PID) 4. WPAN Routing Due to the vital functionality of the PNC in the WPAN, the most capable device in the WPAN is selected as the PNC. The original WPAN standard has presented a set of PNC criteria based on the PNC candidate potential capabilities such as the maximum transmitter power and the maximum association requests the device can handle. The proposed criteria are based on the actual PNC capabilities such as the number of devices directly connected to the PNC candidate. The proposed criteria extension field is designed and integrated within the standard model. The simulation results have proven that the WPAN functionality is improved when the proposed PNC criteria are applied compared to the original criteria. The concepts of user-centricity and user detection have been introduced to the WPAN in order to improve the network friendly-use and to enhance the standard security and data protection. According to the proposed PID design, the network detects the user vicinity and is activated automatically accordingly. The network activity is based on the user location and it follows the nearest device used by the network owner. This is a new feature that is added to the original WPAN standard. Finally, the WPAN routing issue has been studied and analysed. Mathematical model has been designed and analysed for piconet coverage. Accordingly, a new routing approach has been proposed based on the PNC enhancement for routing information.
7

An investigation into MAC layer frame clustering for wirelass LAN intrusion detection

Zhou, Wenzhe January 2006 (has links)
The proliferation of wireless networks has today made security a major concern in the design and operation of these networks. The most popular wireless local area networks (WLANs) are those confonning to the IEEE 802.11 WLAN standards. However, research has shown that there are many vulnerabilities that exist in the wireless MAC layer of these networks that provide opportunities for malicious hackers. Identification of~ttacks occurring inside WLANs is therefore critical to their future developme.nt. This thesis aims at developing a novel MAC frame clustering scheme to solve this problem. This approach is based on the observation that when active events occurs in wireless networks, for example, scanning, joining, and attacking, the management traffic pattern in the MAC layer will be impacted. By analyzing these impacts, MAC layer attacks can be observed and recognized. The methodology involved in this research is machine learning, and a major contribution ofthe work is the classification of attack patterns through observation ofmanagement traffic clusters. The work firstly clusters the MAC management frames into groups which represent corresponding events. For each specific cluster, or event, there are unique patterns. Throug];1/recognizing the patterns of the cluster, attacking clusters can be classified into known categories. The thesis proposes the· above theory and applies it to a MAC layer Intrusion Detection System (IDS) for 802.11 Wireless LANs. This is the first time that a MAC layer IDS has been based on this technique. The IDS consists of six functions: a Traffic Filtration Function (TFF), a Management Traffic Clustering Function (MTCF), an Information Filtration Function (IFF), a First Level Classification (FLC), a Cluster Infonnation Management Function (CIMF) and a Second Level Classification (SLC). The TFF filters the MAC layer management frames and certain information from the filtered frames will be stored in the IFF. The MTCF then clusters the rest of the management frames. A novel clustering algorithm based on a sliding window approach is developed for the MTCF. A two-level classification structure is designed to recognize the cluster types. This two-level structure ensures that the IDS is able to detect unknown pattern attacks and helps decrease system false alarms. The FLC decides whether a cluster represents an abnonnal event based on the content value of the cluster (CCV) and beacon infonnation. When there is an abnonnal event, theSLC is then executed in order to determine the category of the attack according to known patterns. The work has analyzed a variety of 802.11 WLAN MAC layer active attacks and selected thirteen features for classifying the clusters. Support Vector Machine is used as the classification approach. Data captured from the real network test bed are tested on the IDS and the results show high accuracy of detection. The work presented in this thesis is applied in the 802.11 WLANs, however the underlying principles can be applIed to other wireless networks.
8

A cooperative system for enhancing mobile access

Rocha Sa e Moura, Jose Andre January 2011 (has links)
This thesis is in the context of a Next Generation Network environment formed by two or more distinct wireless access technologies covering a public area. These technologies are administered by different mobile operators, where an end-user terminal can connect to any access technology, through the corresponding wireless interface of that multi-interface terminal. In this emergent network environment, congestion will occur very frequently due to a significant increase in the amount of data traffic crossing the network infrastructure. Consequently, the operators must deploy a deployment strategy to cope with high values of data demand, using the available network resources, without compromising the users' connection quality. The work described in this thesis proposes a distributed brokerage service in the heterogeneous network infrastructure that provides a management solution using cooperative strategy from the mobile operators and allowing the terminals to make well informed decisions for their connections. In this way, a closed management loop among that brokerage service at the network and agents at the mobile terminals counteracts any abnormal traffic load. The brokerage service periodically evaluates each technology, combines both wireless and backhaul status in quality metrics and, disseminates these to the client terminals. Depending on the management policies of the brokerage service, the quality metrics and Service Level Agreements (SLAs), diverse classes of service can be supported across the distinct access technologies. The proposed management distributed algorithm proves to be technically robust and stable, because it performs very satisfactorily in diverse scenarios, supporting different management policies, network loads, user mobility patterns and levels of backhaul provisioning. In addition, the impact of deploying the brokerage service in a real scenario with a dynamic business model was studied. This study concludes that the operator who adopts a deployment strategy of enhancing its network infrastructure can be only rewarded from its initial investment when the brokerage service is in operation. In this way, the market operation becomes fairer.
9

Access control scheme for delay/disruption tolerant networks (DTNs)

Johnson, Enyenihi Henry January 2012 (has links)
DelaylDisruption tolerant networks (DTNs) are wireless networks where a complete path from source to destination is not in existence most of the time, and even when it does exist, it is highly unstable and unpredicted. This together with limited computing and storage capacity, heterogeneity and high error rate amongst others violate most of the internet assumptions. This necessitated the design of DTN architecture to relax some of the Internet assumptions and provide interoperabilijy across heterogeneous networks with different network characteristics. The identified security threats in these networks this work is designed to address are masquerading, modification, replay and unauthorized access/use of resources. This work proposes a novel access control scheme that is based on both secret-key and public-key cryptography. The scheme is designed to be independent of server availability and recipient network connectivity during post trust establishment communication. The main contributions in this thesis are: Propose and implement a lightweight asymmetric based Authorization Pass (APass) as an alternative to digital certificate; Design and implement a PKI-based trust management scheme that facilitates secure exchange of public keys without binding it to credential, access control implementation and flexible trust termination process; Propose and implement a trust based authentication scheme that employs Hash-based Message Authentication Code (HMAC) for message authentication and integrity, and APass for source authentication; Investigate and establish the applicability of the push messaging sequence of the generic AAA (Authentication, Authorization and Accounting) architecture with modification, and extend the proposed authentication scheme to implement policy; Propose and implement generic AAA architecture concepts based access control decision making process using DTN Bundle Node. The proposed solutions are extensively discussed with their efficiency and effectiveness as well as comparative advantage demonstrated through simulations.
10

Collaborative multi-Carrier communication techniques for multi-user systems

Gheitanchi, Shahin January 2009 (has links)
Developing robust techniques for fast growing multi-user networks in pervasive environments is an important challenge. Multi-carrier communication is an established technique for achieving superior performance in multi-path frequency selective fading channels. In this thesis, new multi-carrier multiple access techniques using collaborative and cooperative approaches are proposed for multi-user systems in fading environments.

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