Managing data is one of the main challenges in distributed systems and computer science in general. Data is created, shared, and managed across heterogeneous distributed systems of users, services, applications, and devices without a clear and comprehensive data model. This technological fragmentation and lack of a common data model result in a poor understanding of what data is, how it evolves over time, how it should be managed in a distributed system, and how it should be protected and shared. From a user perspective, for example, backing up data over multiple devices is a hard and error-prone process, or synchronising data with a cloud storage service can result in conflicts and unpredictable behaviours. This thesis identifies three challenges in data management: (1) how to extend the current data abstractions so that content, for example, is accessible irrespective of its location, versionable, and easy to distribute; (2) how to enable transparent data storage relative to locations, users, applications, and services; and (3) how to allow data owners to protect data against malicious users and automatically control content over a distributed system. These challenges are studied in detail in relation to the current state of the art and addressed throughout the rest of the thesis. The artefact of this work is the Sea of Stuff (SOS), a generic data model of immutable self-describing location-independent entities that allow the construction of a distributed system where data is accessible and organised irrespective of its location, easy to protect, and can be automatically managed according to a set of user-defined rules. The evaluation of this thesis demonstrates the viability of the SOS model for managing data in a distributed system and using user-defined rules to automatically manage data across multiple nodes.

Peer-to-peer networks and mobile ad hoc networks are emerging distributed networks that share several similarities. Fundamental among these similarities is the decentralized role of each participating node to route messages on behalf of other nodes, and thereby, collectively realizing communication between any pair of nodes. Messages are routed on a topology graph that is determined by the peer relationship between nodes. Although routing is fairly straightforward when the topology graph is static, dynamic variations in the peer relationship that often occur in peer-to-peer and mobile ad hoc networks present challenges to routing. In this thesis, we examine the interplay between routing messages and network topology design in two classes of these networks -- unstructured peer-to-peer networks and sparsely-connected mobile ad hoc networks. In unstructured peer-to-peer networks, we add structure to overlay topologies to support file sharing. Specifically, we investigate the advantages of designing overlay topologies with small-world properties to improve (a) search protocol performance and (b) network utilization. We show, using simulation, that "small-world-like" overlay topologies where every node has many close neighbors and few random neighbors exhibit high chances of locating files close to the source of file search query. This improvement in search protocol performance is achieved while decreasing the traffic load on the links in the underlying network. In the context of sparsely-connected mobile ad hoc networks where nodes provide connectivity via mobility, we present a protocol for routing in space and time where the message forwarding decision involves not only where to forward (space), but also when to forward (time). We introduce space-time routing tables and develop methods to compute these routing tables for those instances of ad hoc networks where node mobility is predictable over either a finite horizon or indefinitely due to periodicity in node motion. Furthermore, when the node mobility is unpredictable, we investigate several forwarding heuristics to address the scarcity in transmission opportunities in these sparsely-connected ad hoc networks. In particular, we present the advantages of fragmenting messages and augmenting them with erasure codes to improve the end-to-end message delivery performance.

Recent advances in pervasive computing and peer-to-peer computing have opened up vast opportunities for developing collaborative applications. To benefit from these emerging technologies, there is a need for investigating techniques and tools that will allow development and deployment of these applications on mobile and heterogeneous platforms. To meet these challenging tasks, we need to address the typical characteristics of mobile peer-to-peer systems such as frequent disconnections, frequent network partitions, and peer heterogeneity. This research focuses on developing the necessary models, techniques and algorithms that will enable us to build and deploy collaborative applications in the Internet enabled, mobile peer-to-peer environments. This dissertation proposes a multi-state transaction model and develops a quality aware transaction processing framework to incorporate quality of service with transaction processing. It proposes adaptive ACID properties and develops a quality specification language to associate a quality level with transactions. In addition, this research develops a probabilistic concurrency control mechanism and a group based transaction commit protocol for mobile peer-to-peer systems that greatly reduces blockings in transactions and improves the transaction commit ratio. To the best of our knowledge, this is the first attempt to systematically support disconnection-tolerant and partition-tolerant transaction processing. This dissertation also develops a scalable directory service called PeerDS to support the above framework. It addresses the scalability and dynamism of the directory service from two aspects: peer-to-peer and push-pull hybrid interfaces. It also addresses peer heterogeneity and develops a new technique for load balancing in the peer-to-peer system. This technique comprises an improved routing algorithm for virtualized P2P overlay networks and a generalized Top-K server selection algorithm for load balancing, which could be optimized based on multiple factors such as proximity and cost. The proposed push-pull hybrid interfaces greatly reduce the overhead of directory servers caused by frequent queries from directory clients. In order to further improve the scalability of the push interface, this dissertation also studies and evaluates different filter indexing schemes through which the interests of each update could be calculated very efficiently. This dissertation was developed in conjunction with the middleware called System on Mobile Devices (SyD).

[Truncated abstract] This thesis develops a scheduled protocol (time division multiple access, TDMA) called flexible-schedule-based TDMA Protocol (FlexiTP), to address the problem of providing end-to-end guarantees on data delivery, whilst also respecting severe resource constraints of wireless sensor networks. FlexiTP achieves this balance through a distributed, synchronised, and loose slot structure in which sensor nodes can build, modify, or extend their schedules based on their local information. In FlexiTP, it is not necessary to predetermine the number of slots required for a network. FlexiTP's local repair scheme allows nodes to adjust their schedules dynamically and autonomously to recover from node and communication faults. Hence, it maintains a reliable and selforganising multihop network. Most sensor network protocols designed for data gathering applications implicitly assume a periodic rate of data collection from all nodes in the network to the base station. However, nodes may want to report their data more rapidly or slowly depending on the significance and importance of their data to the end-user. The problem is that traditional TDMA-based protocols are not flexible to changes in traffic patterns because of their rigid slot structure schemes. This thesis aims to solve this problem by developing an ondemand TDMA slot transfer method that leverages the flexible-slot structure algorithm of FlexiTP to transfer time slots from one part of the network to another part. ... While these communication patterns are sufficient for monitoring applications, individual sensor nodes may need to send their data to multiple destination nodes across the network in order to execute a distributed cooperative-function based on their local environment. This peer-to-peer communication pattern makes sensor networks more reactive to triggers from the environment. This thesis attempts to solve the problem of lack of peer-to-peer communication in the design of a TDMA-driven protocol by extending the idea of on-demand TDMA slot transfer method to allow each sensor node in the network to claim extra time slots to communicate with any other nodes (peers) in the network, without going through the base station. Nodes in the network may have different priorities of data because of event-triggering sensor readings or various types of sensor readings (e.g., light, temperature, and humidity) they provide. When nodes with high priority packets increase the frequency of their data collections, the network bandwidth may be dominated by these nodes. It is desirable to allow nodes with low priority packets to aggregate their packets and so enabling these nodes to send their data to the base station under the current available network bandwidth. This thesis proposes an on-demand data aggregation algorithm that enables sensor nodes to perform an in-network-aggregation based on their current sensing requirements and network capacity constraints. In summary, this thesis describes the design, implementation, and evaluation of protocols for wireless sensor networks that focus on achieving energy-efficiency, provisioning performance assurances, and supporting reactivity and adaptability in constantly changing environment.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The way in which people consume video is changing with the adoption of new technologies such as tablet computers and smart televisions. These new technologies, along with the Internet, are moving video distribution away from satellite and terrestrial broadcast to distribution over the Internet. Services online now offer the same content that originally was only available on satellite broadcast television. However, these services are only viable in countries with high speed, inexpensive Internet bandwidth. The need therefore exists for alternative services to deliver content in countries where bandwidth is still expensive and slow. These include many of the developing nations of Africa. In this thesis we design and develop a video distribution platform that relies on peer-to-peer networking to deliver high quality video content. We use an existing video streaming peer-to-peer protocol as the primary distribution mechanism, but allow users to share video over other protocols and services. These can include BitTorrent, DC++ and users sharing hard drives with one another. In order to protect the video content, we design and implement a security scheme that prevents users from pirating video content, while allowing easy distribution of video data. The core of the security scheme requires a low bandwidth Internet connection to a server that streams keys to unlock the video content. The project also includes the development of a custom video player application to integrate with the security scheme. The platform is not limited to, but is aimed at high speed local area networks where bandwidth is free. In order for the platform to support feasible business models, we provision additional services, such as video cataloging and search, video usage monitoring and platform administration. The thesis includes a literature study on techniques and solutions to secure video entertainment, specifically in a peer-to-peer environment. / AFRIKAANSE OPSOMMING: Die wyse waarvolgens mense video verbruik is aan die verander met die ingebruikneming van nuwe tegnologie soos tabletrekenaars en slim televisiestelle. Hierdie nuwe tegnologie tesame met die Internet maak dat die verspreiding van video al hoe minder plaasvind deur middel van satellietuitsendings en al hoe meer versprei word deur die Internet. Aanlyn-Internetdienste bied deesdae dieselfde inhoud aan as wat voorheen slegs deur beeldsending versprei is. Hierdie dienste is egter slegs lewensvatbaar in lande met hoëspoed- en goedkoop Internetbandwydte. Daar is dus ’n behoefte aan alternatiewe tot hierdie dienste in lande waar bandwydte steeds duur en stadig is. Baie lande in Afrika kan in hierdie kategorie ingesluit word. In hierdie tesis word ’n videoverspreidingsplatform ontwerp en ontwikkel, wat van portuurnetwerke gebruik maak om hoëkwaliteit-beeldmateriaal te versprei. Die stelsel gebruik ’n bestaande portuurnetwerk-datavloeiprotokol as die premêre verspreidingsmeganisme, maar laat gebruikers ook toe om videoinhoud direk met ander gebruikers en dienste te deel. BitTorrent, DC++ en gebruikers wat hardeskywe met mekaar deel word hierby ingesluit. Ten einde die videoinhoud te beskerm ontwerp en implimenteer ons ’n sekuriteitstelsel wat verhoed dat gebruikers die videoinhoud onregmatig kan toe-eien, maar wat terselfdertyd die verspreiding van die data vergemaklik. Hierdie sluit die ontwikkeling van ’n pasgemaakte videospeler in. Die kern van die sekuriteitstelsel benodig ’n lae-bandwydte-Internetverbinding na ’n bediener wat sleutels uitsaai om die videoinhoud te ontsluit. Alhoewel nie daartoe beperk nie, is die platform gemik op hoëspoed-plaaslikegebiedsnetwerke met gratis bandwydte. Om die platvorm aan ’n haalbare sakemodel te laat voldoen het ons vir addisionele dienste soos videokatalogisering met soekfunksies, videoverbruikersmonitering en platvormadministrasie voorsiening gemaak. Die tesis sluit ’n literatuurstudie oor tegnieke en oplossings vir die beskerming van video data, spesifiek in die portuurnetwerke omgeving, in.

The main purpose of this project is to build a bank system that offers a friendly and simple interface to let users easily manage their lightweight currencies. The Lightweight Currency Protocol (LCP) was originally proposed to solve the problem of fairness in resource cooperatives. However, there are other possible applications of the protocol, including the control of spam and as a general purpose medium of exchange for low value transactions. This project investigates the implementation issues of the LCP, and also investigates LCP bank services to provide human interface to currency operations.

A study is done on the protection of sound recordings in the decentralized peer-to-peer (DP2P) file sharing in the United States, the United Kingdom and South Africa. This study reveals that because sound recordings have unique features different from other copyright works, the illegal sharing of sound recordings can ordinarily be filtered, identified, and detected by the Internet service providers (ISPs) before granting access to users and without infringing the users‟ right to privacy. However, the ISPs have failed in this regard, hence, they are strictly held liable under the contributory, vicarious and inducing infringements notwithstanding the statutory law which prohibits ISPs from monitoring, and intercepting their networks. In fact and law, the terms filtering, identifying and detecting on the one hand and monitoring and intercepting on the other hand are different in relation to sound recordings and as such ISPs are not prohibited from filtering, identifying and detecting illegal sound recordings on their networks, thus, ISPs are not protected under the limitation law as it is generally believed. However, several recommendations are made for reform, inter alia: a review of the limitation law to include the terms filtering, identifying and detecting in pursuance of the terms monitoring, and intercepting, if the intention of the legislators was meant to include the latter terms; protection of access right in digital sound recordings, protection of the neighbouring rights of ISPs in the digital world, imposing levies on all recording equipment, the insurability of sound recordings and ISPs‟ signals, and bandwidth. / Mercentile Law / LL. M. (Mercantile Law)

A study is done on the protection of sound recordings in the decentralized peer-to-peer (DP2P) file sharing in the United States, the United Kingdom and South Africa. This study reveals that because sound recordings have unique features different from other copyright works, the illegal sharing of sound recordings can ordinarily be filtered, identified, and detected by the Internet service providers (ISPs) before granting access to users and without infringing the users‟ right to privacy. However, the ISPs have failed in this regard, hence, they are strictly held liable under the contributory, vicarious and inducing infringements notwithstanding the statutory law which prohibits ISPs from monitoring, and intercepting their networks. In fact and law, the terms filtering, identifying and detecting on the one hand and monitoring and intercepting on the other hand are different in relation to sound recordings and as such ISPs are not prohibited from filtering, identifying and detecting illegal sound recordings on their networks, thus, ISPs are not protected under the limitation law as it is generally believed. However, several recommendations are made for reform, inter alia: a review of the limitation law to include the terms filtering, identifying and detecting in pursuance of the terms monitoring, and intercepting, if the intention of the legislators was meant to include the latter terms; protection of access right in digital sound recordings, protection of the neighbouring rights of ISPs in the digital world, imposing levies on all recording equipment, the insurability of sound recordings and ISPs‟ signals, and bandwidth. / Mercentile Law / LL. M. (Mercantile Law)

The aim of this study was to investigate the various reasons consumers continue to infringe on copyrighted content, specifically in the South African context, even if the law forbids it. This investigation is two-fold since it also recognises that there are many individuals who do not infringe on copyrighted content even though they have access to peer-to-peer file sharing technology. This information could prove valuable since it can then be used to find comprehensive market-led solutions to the problem that targets the end-user. This study adopted a mixed method approach in order to cross validate findings and to reveal aspects of empirical reality. The target population for this study consisted of 100 adult South Africans who have access to the internet. Data was collected through an online, self-administered questionnaire. Quantitative data was analysed through descriptive statistics, while qualitative data was analysed through thematic analysis. The results show that there are variety of factors that influence respondents’ attitudes towards copyright infringement of films and/or television series through peer-to-peer file sharing technology, each of which is discussed in detail. The study concluded by identifying 24 factors that favourably influence people’s attitudes towards copyright infringement, including high prices of legitimate goods, historical inequality in South Africa, and perceived low risk of being caught and punished. Based on the conclusion above, the study recommends that policy makers such as government officials, boards of directors, managers, committees, and executives use the results of the study when making decisions and determining policies, especially in the South African context. / Communication Science / M.A. (Communication Science)