On Applications of Disruption Tolerant Networking to Optical Networking in Space

The integration of optical communication links into space networks via Disruption Tolerant Networking (DTN) is a largely unexplored area of research. Building on successful foundational work accomplished at JPL, we discuss a multi-hop multi-path network featuring optical links. The experimental test bed is constructed at the NASA Glenn Research Center featuring multiple Ethernet-to-fiber converters coupled with free space optical (FSO) communication channels. The test bed architecture models communication paths from deployed Mars assets to the deep space network (DSN) and finally to the mission operations center (MOC). Reliable versus unreliable communication methods are investigated and discussed; including reliable transport protocols, custody transfer, and fragmentation. Potential commercial applications may include an optical communications infrastructure deployment to support developing nations and remote areas, which are unburdened with supporting an existing heritage means of telecommunications. Narrow laser beam widths and control of polarization states offer inherent physical layer security benefits with optical communications over RF solutions. This paper explores whether or not DTN is appropriate for space-based optical networks, optimal payload sizes, reliability, and a discussion on security

Livenet: A low-latency video transport network for large-scale live streaming

Low-latency live streaming has imposed stringent latency requirements on video transport networks. In this paper we report on the design and operation of the Alibaba low-latency video transport network, LiveNet. LiveNet builds on a flat CDN overlay with a centralized controller for global optimization. As part of this, we present our design of the global routing computation and path assignment, as well as our fast data transmission architecture with fine-grained control of video frames. The performance results obtained from three years of operation demonstrate the effectiveness of LiveNet in improving CDN performance and QoE metrics. Compared with our prior state-of-The-Art hierarchical CDN deployment, LiveNet halves the CDN delay and ensures 98% of views do not experience stalls and that 95% can start playback within 1 second. We further report our experiences of running LiveNet over the last 3 years

On the use of IEEE 802.15.4/ZigBee as federating communication protocols for Wireless Sensor Networks

Tese de mestrado. Redes e Serviços de Comunicação. Faculdade de Engenharia. Universidade do Porto, Instituto Superior de Engenharia. 200

A Multi-Hop 6LoWPAN Wireless Sensor Network for Waste Management Optimization

In the first part of this Thesis several Wireless Sensor Network technologies, including the ones based on the IEEE 802.15.4 Protocol Standard like ZigBee, 6LoWPAN and Ultra Wide Band, as well as other technologies based on other protocol standards like Z-Wave, Bluetooth and Dash7, are analyzed with respect to relevance and suitability with the Waste Management Outsmart European FP7 Project. A particular attention is given to the parameters which characterize a Large Scale WSN for Smart Cities, due to the amount of sensors involved and to the practical application requested by the project. Secondly, a prototype of sensor network is proposed: an Operative System named Contiki is chosen for its portability on different hardware platforms, its Open Source license, for the use of the 6LoW-PAN protocol and for the implementation of the new RPL routing protocol. The Operative System is described in detail, with a special focus on the uIPv6 TCP/IP stack and RPL implementation. With regard to this innovative routing proto col designed specifically for Low Power Lossy Networks, chapter 4 describes in detail how the network topology is organized as a Directed Acyclic Graph, what is an RPL Instance and how downward and upward routes are constructed and maintained. With the use of several AVR Atmel modules mounting the Contiki OS a real WSN is created and, with an Ultrasonic Sensor, the filling level of a waste basket prototype is periodically detected and transmitted through a multi-hop wireless network to a sink nodeope

Remote vital signs monitoring based on wireless sensor networks

Tese de doutoramento em Líderes para as Indústrias TecnológicasGovernmental and private institutions face a major challenge to provide quality health care to a population consisting of a growing number of elderly and chronically ill patients. According to the World Health Organization, in 2006, the total global health expenditures exceeded US$ 4 trillion and are rising in the majority of countries including Portugal which, during 2006, expended 9.9% of its gross domestic product in health care. The use of remote vital signs monitoring systems increases the probability of early detection of risky situations, allows frequent monitoring of in-patients, elderly and chronically ill patients, and streamlines the work of health professionals. However, at present, these systems are expensive, complex and employ obtrusive sensors, which limit their application to intensive care units and cardiac intermediate care units. This work is part of a project that aims to design, prototype and evaluate a remote vital signs monitoring system based on the IEEE 802.15.4 and ZigBee protocols, which allow the development of small low-power sensors. The prototype system comprises electrocardiogram/heart rate and axillary thermometer sensors, networking devices and three informatics applications that collect, process, and exhibit medical data. The wireless sensors, the networking devices and one of the applications were developed under this work. Additionally, the wireless sensor network was evaluated through simulations at the MAC level and experimental and field tests. Field tests were performed at an in-patient floor of Hospital Privado de Guimarães, a Portuguese hospital. Finally, questionnaires were used to measure the satisfaction of users and catalog their critics and suggestions for improvement. Simulations considered different topologies, operation modes and a crescent number of sensors and hops. Experimental and field tests confirmed most of the results obtained by simulations, but revealed that networks which did not assign transmission time slots to electrocardiogram sensors were unable to maintain a high delivery ratio. Contention between devices, aggravated by the inability of routers in receiving incoming packets during backoff, and collisions between packets generated by hiddennodes were responsible for most message losses. On the other hand, beacon-enabled star IEEE 802.15.4 networks that assigned a guaranteed time slot to sensors were able to maintain a very high delivery ratio. In contrast, these networks are restricted in terms of the coverage area and the number of sensors. Also, field tests showed that under low traffic scenarios ZigBee nonbeacon-enabled networks can achieve a high delivery ratio even in presence of a high percentage of hidden-nodes.Instituições governamentais e privadas enfrentam um grande desafio para prestar cuidados de saúde de qualidade a uma população constituída por um número crescente de idosos e doentes crónicos. Segundo a Organização Mundial de Saúde, em 2006, a despesa mundial em saúde ultrapassou a quantia de 4 bilhões de dólares americanos e cresce anualmente na maioria dos países, incluindo Portugal, o qual, em 2006, gastou 9,9% do seu produto interno bruto em cuidados de saúde. O uso de sistemas de monitorização remota de sinais vitais aumenta a probabilidade de deteção precoce de situações de risco, permite que doentes internados, idosos ou doentes crónicos sejam frequentemente monitorizados e agiliza o trabalho dos profissionais de saúde. No entanto, atualmente, estes sistemas são caros e complexos, o que limita a sua aplicação a alguns setores dos hospitais, tais como as unidades de cuidados intensivos e as unidades de cuidados intermédios na área da cardiologia. O projeto no qual insere-se este trabalho visa a conceção, a prototipagem e a avaliação de um sistema de monitorização remota de sinais vitais com base nos protocolos IEEE 802.15.4 e ZigBee, os quais oferecem a possibilidade de construção de sensores com consumos energéticos muito baixos e reduzidas dimensões. O sistema consiste em sensores de eletrocardiograma/frequência cardíaca e temperatura axilar, dispositivos de rede e três aplicações que coletam, processam e apresentam o eletrocardiograma e os sinais vitais. No âmbito deste trabalho foram desenvolvidos os sensores sem fios, os dispositivos de rede e uma das aplicações informáticas. Além disso, foi feita a avaliação do desempenho da rede de sensores sem fios através da análise de simulações a nível da camada de acesso ao meio (MAC) e de testes de laboratório e de campo. Os testes de campo da rede de sensores sem fios foram executados em um dos pisos de internamento do Hospital Privado de Guimarães. Finalmente, foram usados questionários para medir a satisfação dos utilizadores e recolher críticas e sugestões de melhoria. As simulações consideraram diferentes topologias e modos de operação, além de um número crescente de sensores e saltos. Testes experimentais e de campo confirmaram grande parte dos resultados obtidos por simulação mas, adicionalmente, revelaram que as redes constituídas por vários sensores de eletrocardiograma e que não reservaram um intervalo de tempo de transmissão aos sensores não foram capazes de manter uma elevada taxa de entrega de mensagens. Perdas de mensagens ocorreram devido a disputas entre sensores pelo acesso ao canal sem fios e devido a ocorrência de colisões de pacotes transmitidos por nós escondidos. Por outro lado, as redes baseadas no protocolo IEEE 802.15.4 que atribuíram um intervalo de tempo de transmissão a cada sensor conseguiram manter uma elevada taxa de entrega. Entretanto, essas redes são limitadas em termos da área de cobertura e do número de sensores. Adicionalmente, durante os testes de campo em cenários de tráfego reduzido, as redes ZigBee que não empregaram beacons atingiram uma elevada taxa de entrega mesmo na presença de uma grande percentagem de nós escondidos

A survey of self organisation in future cellular networks

This article surveys the literature over the period of the last decade on the emerging field of self organisation as applied to wireless cellular communication networks. Self organisation has been extensively studied and applied in adhoc networks, wireless sensor networks and autonomic computer networks; however in the context of wireless cellular networks, this is the first attempt to put in perspective the various efforts in form of a tutorial/survey. We provide a comprehensive survey of the existing literature, projects and standards in self organising cellular networks. Additionally, we also aim to present a clear understanding of this active research area, identifying a clear taxonomy and guidelines for design of self organising mechanisms. We compare strength and weakness of existing solutions and highlight the key research areas for further development. This paper serves as a guide and a starting point for anyone willing to delve into research on self organisation in wireless cellular communication networks

IoT and Smart Cities: Modelling and Experimentation

Internet of Things (IoT) is a recent paradigm that envisions a near future, in which the objects of everyday life will communicate with one another and with the users, becoming an integral part of the Internet. The application of the IoT paradigm to an urban context is of particular interest, as it responds to the need to adopt ICT solutions in the city management, thus realizing the Smart City concept. Creating IoT and Smart City platforms poses many issues and challenges. Building suitable solutions that guarantee an interoperability of platform nodes and easy access, requires appropriate tools and approaches that allow to timely understand the effectiveness of solutions. This thesis investigates the above mentioned issues through two methodological approaches: mathematical modelling and experimenta- tion. On one hand, a mathematical model for multi-hop networks based on semi- Markov chains is presented, allowing to properly capture the behaviour of each node in the network while accounting for the dependencies among all links. On the other hand, a methodology for spatial downscaling of testbeds is proposed, implemented, and then exploited for experimental performance evaluation of proprietary but also standardised protocol solutions, considering smart lighting and smart building scenarios. The proposed downscaling procedure allows to create an indoor well-accessible testbed, such that experimentation conditions and performance on this testbed closely match the typical operating conditions and performance where the final solutions are expected to be deployed

Modeling and experimental performance analysis of ZigBee-IEEE 802.15.4 for wireless body area networks

Dissertação de mestrado integrado em Engenharia de ComunicaçõesThe emerging field of wireless body area networks (WBAN) has the potential to play an important role in everyday life, and there are many industries such as health, sports and entertainment that can take advantage of these networks. The wireless monitoring of users’ physical state, in indoor or outdoor environments, can bring benefits in several application scenarios; for example, it can increase patients’ general well-being and reduce caregivers’ workload by allowing continuous monitoring. This dissertation identifies and analyzes key performance aspects of using the ZigBee and IEEE 802.15.4 protocols in WBAN applications. The main reason behind this work is because these protocols were designed primarily for wireless sensor networks (WSNs) but are also being used in WBAN applications, particularly in the healthcare area. The differences between WSN and WBANs are explained and are used to discuss the usage of the ZigBee and the IEEE 802.15.4 standards in WBANs. The analysis performed in this work consists mainly in the execution of experimental tests with non-beacon enabled ZigBee/IEEE 802.15.4 networks, using widespread hardware and software platforms from Texas Instruments, regarding relevant quality of service (QoS) metrics (maximum throughput, delivery ratio and network delay), as well as the effects of multiple constraints, such as hidden nodes, clock drift and body interference in the network performance. A clock drift model was proposed to estimate when two nodes will interfere with each other. This model was conceived due to the lack of support from the ZigBee to overcome this issue. A solution to overcome the clock drift and the hidden node problems was then designed. A parametric software delay model of ZigBee network devices was also defined and introduced into a simulator so that more accurate simulation results could be obtained. The proposed models were deemed valid since they were thoroughly tested and the predicted results were obtained.As redes de sensores sem fios de área corporal (WBAN) têm o potencial de desempenhar um papel importante no dia-a-dia. Hoje em dia há muitas indústrias, tais como na área da saúde, do desporto e do entretenimento, que podem tirar proveito dessas redes. A monitorização sem fios de sinais fisiológicos, tanto em ambientes fechados como ao ar livre, pode trazer benefícios em vários cenários de aplicação, tais como, aumentar o bem-estar de pacientes que são monitorizados e reduzir a carga de trabalho de médicos, permitindo a monitorização contínua. Esta dissertação identifica e analisa aspetos chave do desempenho das redes ZigBee e IEEE 802.15.4, quando usadas em aplicações típicas das WBAN. A principal motivação para a realização deste trabalho reside no facto de que, apesar de terem sido projetados principalmente para redes de sensores sem fio (WSN), estes protocolos estão também a ser utilizados em aplicações características das WBAN, particularmente na área da saúde. As diferenças entre as WSN e as WBAN são destacadas e usadas para discutir o uso dos protocolos ZigBee e IEEE 802.15.4 nas WBAN. A análise realizada neste trabalho consiste, principalmente, na execução de testes experimentais de redes ZigBee/IEEE 802.15.4 a funcionar no modo non-beacon enabled, usando as plataformas de hardware e software da Texas Instruments. A análise leva em consideração métricas relevantes (o máximo goodput, a taxa de entrega e o atraso da rede) de qualidade de serviço (QoS) e os efeitos de várias condicionantes, como os nós escondidos, o clock drift e a interferência do corpo humano no desempenho da rede. Um modelo para o clock drift foi proposto para estimar quando dois dispositivos irão interferir um com o outro devido a este fenómeno. Este modelo foi concebido devido à falta de capacidade para o ZigBee superar este problema. Posteriormente foi concebida uma solução para ultrapassar os problemas associados ao clock drift e aos nós escondidos. Um modelo paramétrico de atrasos de software em dispositivos de redes ZigBee foi também definido e introduzido num simulador, de modo a que resultados de simulações mais precisos possam ser obtidos. Os modelos propostos foram considerados válidos dado que foram testados e os resultados previstos foram obtidos