Complex networks like the Internet, peer-to-peer systems, and emerging sensor and ad-hoc networks are large distributed decentralized communication systems arising repeatedly in today's technology. In such networks it is critical to characterize network performance as the size of the network scales. The focus of my work is to relate basic network performance metrics to structural characteristics of underlying network topologies, and to develop protocols that reinforce and exploit desired structural characteristics. For the case of the Internet at the Autonomous System level, we relate the graph theoretic notions of conductance and spectrum to network clustering and network congestion. In particular, we show how spectral analysis can identify clusters, and how the presence of clusters affects congestion. This is important for network prediction and network simulation. For the case of peer-to-peer networks we relate conductance and spectral gap to the fundamental questions of searching and topology maintenance. We propose new protocols for maintaining peer-to-peer networks with good conductance and low network overhead. We compare the performance of the traditional method of search by flooding to searching by random walks. We isolate cases of practical interest, such as clustered and dynamic network topologies, where the latter have superior performance. The improvement in the performance can be directly quantified in terms of the conductance of the underlying topology. We introduce further hybrid search schemes, of which flooding and random walks are special instances, which aim to improve the performance of searching by using locally maintained information about the network topology.

Frameworks have been used since the early eighties. Now that frameworks are becoming increasingly popular, several problems are surfacing. Those problems can be categorized into evolution problems (i.e. problems with changes over time) and composition problems (i.e. problems that occur when more than one framework is used in an application). This master thesis focusses on preventing these problems in an early stage in the development of a framework. Guidelines for building OO Frameworks are presented and the guidelines are tried out in the domain of communication protocols.

<p> Wireless communication technologies, such as cellular ones, Bluetooth, and WiFi, are fundamental for today’s and tomorrow’s communication infrastructure. Networks based on those technologies are or will be increasingly deployed in many critical domains, such as critical infrastructures, smart cities, healthcare, and industrial environments. Protecting wireless networks against attacks and privacy breaches is thus critical. A fundamental step for the security and privacy of these networks is ensuring that their protocols are implemented as mandated by the standards. These protocols are however quite complex and unfortunately, the lack of secure-by-design approaches for these complex protocols often induces vulnerabilities in implementations with severe security and privacy repercussions. For these protocols, the standards are thousands of pages long, written in natural language, describe the high-level interaction of the protocol entities, and most often depend on human interpretation—which is open to misunderstanding and ambiguity. This inherently entails the question of whether these wireless protocols and their communication equipment implement the corresponding standards correctly or whether the implementations introduce vulnerabilities that can have severe consequences.</p>

The demands of a modern way of life have changed the way power electronics systems work. For instance, the grid has to provide not only the service of delivering electrical energy but also the communication to enable interactions between customers and enable them to be producers of electrical energy, too. Thus, the smart grid has come into existence. The consequence of the smart grid is that consumers could be “smart.” The most obvious consumers are households, so the houses have to also be smart and must be equipped with various power electronics devices for producing and managing electrical energy. Again, all those devices have to communicate somehow and provide data for managing electrical energy in the house. Zoomed in further, novel, state-of-the-art measurement equipment could have been built from different power electronics devices, and communication among them would be necessary for good operation. Zoomed further in, communication among different pieces of power electronics devices (such as converters) could offer benefits such as flexibility, abstraction, and modularity. This thesis provides insight into different communication techniques and protocols used in power electronics systems. A top-down approach presents three different levels of communication used in real-life projects with all the challenges they bring, starting with the smart house, followed by the state-of-the-art impedance measurement unit, and finalizing with internal power electronics building block (PEBB) communication. In the case of a smart house, where the house is equipped with solar panels, charge controllers, batteries, and inverters, communication allows interoperation between different elements of the power electronics system, enabling energy management. Results show the operation of the system and energy management algorithm. A house of this type won first prize at an international competition where energy management was one of the disciplines. The impedance measurement unit consists of different power electronics devices. In this case, too, communication between devices enables the operation of the impedance measurement unit. Communication techniques used here are shown together with measurement results. Finally, inter-PEBB communication has been shown as an approach for interaction among the different elements inside the PEBB, such as controller, GDs, sensors, and actuators. Real-time communication protocol, including all challenges, is described and developed. This approach is shown to enable communication and synchronization among different nodes inside the PEBB. Communication enables all internal elements of the PEBB to be transparent outside the PEBB in the sense that data gathered from them could be reused anywhere else in the system. Also, this approach enables the development of distributed event (time) driven control, hardware and software, abstraction, high modularity, and flexibility. A very important aspect of inter-PEBB communication is synchronization. A simple technique of sharing a clock among the parts of a 6 kV PEBB has been shown. / M.S. / This thesis provides insight into different communication techniques and protocols used in power electronics systems. A top-down approach presents three different levels of communication used in real-life projects with all the challenges they bring, starting with the smart house and a custom device designed and developed to be a communication interface among different power electronics devices from different vendors, such as charge controllers or inverters, but with capabilities not only to communicate but to also provide a platform for the development of energy management algorithms used to make houses grid zero if not grid positive. Aside from the smart house, this thesis describes communication protocols and techniques used in the impedance measurement unit (IMU). This complex measurement device provides valuable and accurate impedance measurements and consists of different power electronics devices that need to communicate. Finally, at the power electronics building block (PEBB) level, real-time communication protocol with all challenges is described. Developed communication protocol provides communication and synchronization among different nodes such as GDs, sensors, and actuators inside the PEBB. This intra-PEBB communication and synchronization combined with inter-PEBB communication and synchronization provide the foundation for the development of truly distributed event- (time-) driven control as well as hardware and software abstraction.

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / The Data Acquisition, Analysis, and Simulation System (DAAS) is a computer system designed to allow data sources on spacecraft in the Flight System Testbed (FST) to be monitored, analyzed, and simulated. This system will be used primarily by personnel in the Flight System Testbed, flight project designers, and test engineers to investigate new technology that may prove useful across many flight projects. Furthermore, it will be used to test various spacecraft design possibilities during prototyping. The basic capabilities of the DAAS involve unobtrusively monitoring various information sources on a developing spacecraft. This system also provides the capability to generate simulated data in appropriate formats at a given data rate, and to inject this data onto the communication line or bus, using the necessary communication protocol. The DAAS involves Serial RS232/RS422, Ethernet, and MIL-STD-1553 communication protocols, as well as LabVIEW software, VME hardware, and SunOS/UNIX operating systems.

Sensor nodes are deployed over sensing fields for the purpose of monitoring certain phenomena of interest. The sensor nodes perform specific measurements, process the sensed data, and send the data to a base station over a wireless channel. The base station collects data from the sensor nodes, analyses this data, and reports it to the users. Wireless sensor networks are different from traditional networks, because of the following constraints. Typically, a large number of sensor nodes need to be randomly deployed and, in most cases, they are deployed in unreachable environments; however, the sensor nodes may fail, and they are subject to power constraints. Energy is one of the most important design constraints of wireless sensor networks. Energy consumption, in a sensor node, occurs due to many factors, such as: sensing the environment, transmitting and receiving data, processing data, and communication overheads. Since the sensor nodes behave as router nodes for data propagation, of the other sensor nodes to the base station, network connectivity decreases gradually. This may result in disconnected sub networks of sensor nodes. In order to prolong the network's lifetime, energy efficient protocols should be designed for the characteristics of the wireless sensor network. Sensor nodes in different regions of the sensing field can collaborate to aggregate the data that they gathered. Data aggregation is defined as the process of aggregating the data from sensor nodes to reduce redundant transmissions. It reduces a large amount of the data traffic on the network, it requires less energy, and it avoids information overheads by not sending all of the unprocessed data throughout the sensor network. Grouping sensor nodes into clusters is useful because it reduces the energy consumption. The clustering technique can be used to perform data aggregation. The clustering procedure involves the selection of cluster heads in each of the cluster, in order to coordinate the member nodes. The cluster head is responsible for: gathering the sensed data from its cluster's nodes, aggregating the data, and then sending the aggregated data to the base station. An adaptive clustering protocol was introduced to select the heads in the wireless sensor network. The proposed clustering protocol will dynamically change the cluster heads to obtain the best possible performance, based on the remaining energy level of sensor nodes and the average energy of clusters. The OMNET simulator will be used to present the design and implementation of the adaptive clustering protocol and then to evaluate it. This research has conducted extensive simulation experiments, in order to fully study and analyse the proposed energy efficient clustering protocol. It is necessary for all of the sensor nodes to remain alive for as long as possible, since network quality decreases as soon as a set of sensor nodes die. The goal of the energy efficient clustering protocol is to increase the lifetime and stability period of the sensor network. This research also introduces a new bidirectional data gathering protocol. This protocol aims to form a bidirectional ring structure among the sensor nodes, within the cluster, in order to reduce the overall energy consumption and enhance the network's lifetime. A bidirectional data gathering protocol uses a source node to transmit data to the base station, via one or more multiple intermediate cluster heads. It sends data through energy efficient paths to ensure the total energy, needed to route the data, is kept to a minimum. Performance results reveal that the proposed protocol is better in terms of: its network lifetime, energy dissipation, and communication overheads.

This research studies the security challenges in IoT devices. At first, security challenges have been described and then specifically the security of communication protocols in the IoT has been addressed. Finally, among different communication protocols, ZigBee and Z-Wave protocols have been chosen for this study. The criterion for choosing these two protocols is the level of security they provide for IoT devices to protect them against unauthorized access and hacking. Security, frequency, power consumption and data rate are the characteristics that have been discussed in the review of these two protocols. In the end, a comparison of the various features of these two protocols clarified that the security of IoT devices in each of these protocols depends on the type of the IoT device, the required range and other requirements, however, in most cases the ZigBee protocol showed more security than Z-Wave.

Nas subestações das grandes concessionárias de distribuição de energia elétrica coexistem sistemas de proteção com diferentes tecnologias, formados por relés eletromecânicos, estáticos e digitais, que, em alguns casos, continuarão funcionando por algumas décadas. Essa diversidade de tecnologias implica em sistemas com características de hardware e software diferentes, o que dificulta a implantação de funcionalidades locais e remotas que sejam interoperáveis. Dessa forma, torna-se interessante desenvolver um sistema baseado nas diferentes plataformas de proteção do mercado, com o objetivo de integrar as informações dos relés de proteção de diferentes tecnologias e que se comunicam através de protocolos distintos, criando uma base de dados homogênea. Para isso é necessário realizar uma coleta de dados provenientes dos vários relés de proteção e disponibilizar as informações do sistema de proteção para uma base de dados, através de uma interface de protocolos, onde essas informações possam ser tratadas de maneira uniforme e organizadas de forma estruturada, otimizando a funcionalidade local da instalação e podendo alimentar um sistema central de gestão. / In substations of large electric power distribution companies coexist protection systems with different technologies, comprised of electromechanical, static and digital relays that, in some cases, will continue to work for a few decades. This technology diversity implies in systems with different features of hardware and software, which hampers the implementation of local and remote functionalities that are interoperable. It would be interesting to develop a system based on integrated functional use of different protection platforms on the market, aiming to integrate the information of protective relays from different technologies that communicate with different protocols, creating a homogeneous database. It would be necessary a collection of data from the various protection relays that, through an interface protocols, provide information from the protection system for a database where information can be treated uniformly and organized in a structured manner, optimizing the local functionalities and feeding a central management system.

Nas subestações das grandes concessionárias de distribuição de energia elétrica coexistem sistemas de proteção com diferentes tecnologias, formados por relés eletromecânicos, estáticos e digitais, que, em alguns casos, continuarão funcionando por algumas décadas. Essa diversidade de tecnologias implica em sistemas com características de hardware e software diferentes, o que dificulta a implantação de funcionalidades locais e remotas que sejam interoperáveis. Dessa forma, torna-se interessante desenvolver um sistema baseado nas diferentes plataformas de proteção do mercado, com o objetivo de integrar as informações dos relés de proteção de diferentes tecnologias e que se comunicam através de protocolos distintos, criando uma base de dados homogênea. Para isso é necessário realizar uma coleta de dados provenientes dos vários relés de proteção e disponibilizar as informações do sistema de proteção para uma base de dados, através de uma interface de protocolos, onde essas informações possam ser tratadas de maneira uniforme e organizadas de forma estruturada, otimizando a funcionalidade local da instalação e podendo alimentar um sistema central de gestão. / In substations of large electric power distribution companies coexist protection systems with different technologies, comprised of electromechanical, static and digital relays that, in some cases, will continue to work for a few decades. This technology diversity implies in systems with different features of hardware and software, which hampers the implementation of local and remote functionalities that are interoperable. It would be interesting to develop a system based on integrated functional use of different protection platforms on the market, aiming to integrate the information of protective relays from different technologies that communicate with different protocols, creating a homogeneous database. It would be necessary a collection of data from the various protection relays that, through an interface protocols, provide information from the protection system for a database where information can be treated uniformly and organized in a structured manner, optimizing the local functionalities and feeding a central management system.

Electronic document handling was first used in the automotive industry in the early 1970’s, the way of communicating electronic at the time was concerned with the communication way of EDI (Hsieh, 2004). In the beginning of 2000 a new way of communicating electronic documents was introduced with the emergence of VAN-operators (Hsieh, 2004). This technology of communicating electronic invoices has shown to be less complex for the businesses than the previous EDI connections. The VAN-operators enable companies regardless of size, ERP, also known as Enterprise Resource Planning, system, formats or transaction volume to send and receive electronic invoices. The subject of electronic invoice handling have become increasingly debated, mainly because of the legislations taking place all over Europe, and as well as the environmental impact by business transactions being sent by paper. The objective of this thesis is to examine the challenges, solutions and outcomes for companies switching to electronic invoice handling. The data collected for the thesis is divided into two parts. The first part consist of information retrieved by previous literature as well as internet sources. The second part concerns the case studies conducted for the thesis in respect to our research questions. For this reason Scandinavian companies have been interviewed, with different precondition as in size, industry, transaction volume and IT structure. The findings from the first and second part have been analyzed and conclusion have been made, we suggest using a VAN-operators, which have shown to be the most appropriate alternative for companies that are implementing electronic invoice handling. The result of this thesis can be used as a guideline for companies when considering a switch from manual to electronic invoice handling.