With the increasing pervasiveness of mobile technologies such as cellular phones, personal digital assistants and hand held computers, mobile technologies promise the next major technological and cultural shift. Like the Internet, it is predicted that the greatest impact will not come from hardware devices or software programs, but from emerging social practices, which were not possible before. To capitalize on the benefits of mobile technologies, organizations have begun to implement nomadic computing environments. Nomadic computing environments make available the systems support needed to provide computing and communication capabilities and services to the mobile work force as they move from place to place in a manner that is transparent, integrated, convenient and adaptive. Already, anecdotes suggest that within organizations there are social implications occurring with both unintended and intended consequences being perpetuated. The problems of nomadic computing users have widely been described in terms of the challenges presented by the interplay of time, space and context, yet a theory has yet to be developed which analyzes this interplay in a single effort. A temporal human agency perspective proposes that stakeholders’ actions are influenced by their ability to recall the past, respond to the present and imagine the future. By extending the temporal human agency perspective through the recognition of the combined influence of space and context on human action, I investigated how the individual practices of eleven nomadic computing users changed after implementation. Under the umbrella of the interpretive paradigm, and using a cross case methodology this research develops a theoretical account of how several stakeholders engaged with different nomadic computing environments and explores the context of their effectiveness. Applying a literal and theoretical replication strategy to multiple longitudinal and retrospective cases, six months were spent in the field interviewing and observing participants. Data analysis included three types of coding: descriptive, interpretive and pattern coding. The findings reveal that patterns of technology use in nomadic computing environments are influenced by stakeholders’ temporal orientations; their ability to remember the past, imagine the future and respond to the present. As stakeholders all have different temporal orientations and experiences, they exhibit different practices even when engaging initially with the same organizational and technical environments. Opposing forces emerge as users attempt to be effective by resolving the benefits and disadvantages of the environment as they undergo different temporal, contextual and spatial experiences. Insights about the ability to predict future use suggest that because they are difficult to envisage in advance, social processes inhibit the predictability of what technologies users will adopt. The framework presented highlights the need to focus on understanding the diversity in nomadic computing use practices by examining how they are influenced by individual circumstances as well as shared meanings across individuals.

Delay-tolerant networks (DTNs) have the potential to connect devices and areas of the world that are under-served by traditional networks. The idea is that an end-to-end connection may never be present. To make communication possible, intermediate nodes take custody of the data being transferred and forward it as the opportunity arises. Both links and nodes may be inherently unreliable and disconnections may be long-lived. A critical challenge for DTNs is determining routes through the network without ever having an end-to-end connection. <br /><br /> This thesis presents a practical routing protocol that uses only observed information about the network. Previous approaches either require complete future knowledge about the connection schedules, or use many copies of each message. Instead, our protocol uses a metric that estimates the average waiting time for each potential next hop. This learned topology information is distributed using a link-state routing protocol, where the link-state packets are flooded using epidemic routing. The routing is recomputed each time connections are established, allowing messages to take advantage of unpredictable contacts. Messages are exchanged if the topology suggests that a connected node is "closer" than the current node. <br /><br /> Simulation results are presented, showing that the protocol provides performance similar to that of schemes that have global knowledge of the network topology, yet without requiring that knowledge. Further, it requires a significantly less resources than the epidemic alternative, suggesting that this approach scales better with the number of messages in the network.

Delay-tolerant networks (DTNs) have the potential to connect devices and areas of the world that are under-served by traditional networks. The idea is that an end-to-end connection may never be present. To make communication possible, intermediate nodes take custody of the data being transferred and forward it as the opportunity arises. Both links and nodes may be inherently unreliable and disconnections may be long-lived. A critical challenge for DTNs is determining routes through the network without ever having an end-to-end connection. <br /><br /> This thesis presents a practical routing protocol that uses only observed information about the network. Previous approaches either require complete future knowledge about the connection schedules, or use many copies of each message. Instead, our protocol uses a metric that estimates the average waiting time for each potential next hop. This learned topology information is distributed using a link-state routing protocol, where the link-state packets are flooded using epidemic routing. The routing is recomputed each time connections are established, allowing messages to take advantage of unpredictable contacts. Messages are exchanged if the topology suggests that a connected node is "closer" than the current node. <br /><br /> Simulation results are presented, showing that the protocol provides performance similar to that of schemes that have global knowledge of the network topology, yet without requiring that knowledge. Further, it requires a significantly less resources than the epidemic alternative, suggesting that this approach scales better with the number of messages in the network.

Este trabalho explora a gerência de segurança e cooperação de aplicações em sistemas distribuídos móveis. Neste contexto, é feito um estudo sobre os diferentes middlewares para ambientes móveis (mobile middleware): suas capacidades de enfrentar os desafios da mobilidade e da segurança. As análises do estudo mostram que esses middlewares devem possuir características que lhes permitem uma melhor adaptação às necessidades das aplicações e à natureza dos ambientes móveis. Os middlewares existentes pouco abordam a questão da segurança. A segurança ainda é um problema complexo que deve ser gerido em todos os níveis de um sistema distribuído móvel, incluindo novos mecanismos. Com base nessa análise, foi desenvolvido um modelo de gerência de segurança que implementa um mecanismo de autenticação mútua, confidencialidade, detecção de intruso e controle de acesso em ambientes móveis. O objetivo é garantir a confiabilidade, a disponibilidade de serviços e a privacidade do usuário através da tecnologia PET - Privacy-Enhancing Tecnologies. A idéia é fundamentada em agentes interceptadores e autoridades de segurança que distribuem tíquetes de segurança e controlam o acesso a recursos e espaços de tuple do ambiente. O estudo de caso apresentou resultados satisfatórios que permitem julgar a pertinência do modelo proposto. O modelo será integrado a um sistema de e-saúde. / The work exploits the security management and the cooperation of applications in mobile distributed systems. In this context a study of different mobile middleware is made. The study examines their capacities to face the challenges of mobility and security issues. The analysis shows that the existing middleware has very few approaches on security problems; security is still a complex issue to be managed in all the levels of mobile distributed system including new mechanisms. Based on this analysis, a security management model is developed that implements a mechanism for mutual authentication, confidentiality, intrusion detection, access control of mobile agents in mobile environments, ensures services availability and user privacy, through technology PET (Privacy-Enhancing Technologies). The idea is based on interceptor agents and security authorities that distribute security tickets and control the access to resources and Tuple spaces in mobile environment. The proposed model presents good performance and is integrated to an e-health system: Relationship Management with Chronic Patient GRPC.

Este trabalho explora a gerência de segurança e cooperação de aplicações em sistemas distribuídos móveis. Neste contexto, é feito um estudo sobre os diferentes middlewares para ambientes móveis (mobile middleware): suas capacidades de enfrentar os desafios da mobilidade e da segurança. As análises do estudo mostram que esses middlewares devem possuir características que lhes permitem uma melhor adaptação às necessidades das aplicações e à natureza dos ambientes móveis. Os middlewares existentes pouco abordam a questão da segurança. A segurança ainda é um problema complexo que deve ser gerido em todos os níveis de um sistema distribuído móvel, incluindo novos mecanismos. Com base nessa análise, foi desenvolvido um modelo de gerência de segurança que implementa um mecanismo de autenticação mútua, confidencialidade, detecção de intruso e controle de acesso em ambientes móveis. O objetivo é garantir a confiabilidade, a disponibilidade de serviços e a privacidade do usuário através da tecnologia PET - Privacy-Enhancing Tecnologies. A idéia é fundamentada em agentes interceptadores e autoridades de segurança que distribuem tíquetes de segurança e controlam o acesso a recursos e espaços de tuple do ambiente. O estudo de caso apresentou resultados satisfatórios que permitem julgar a pertinência do modelo proposto. O modelo será integrado a um sistema de e-saúde. / The work exploits the security management and the cooperation of applications in mobile distributed systems. In this context a study of different mobile middleware is made. The study examines their capacities to face the challenges of mobility and security issues. The analysis shows that the existing middleware has very few approaches on security problems; security is still a complex issue to be managed in all the levels of mobile distributed system including new mechanisms. Based on this analysis, a security management model is developed that implements a mechanism for mutual authentication, confidentiality, intrusion detection, access control of mobile agents in mobile environments, ensures services availability and user privacy, through technology PET (Privacy-Enhancing Technologies). The idea is based on interceptor agents and security authorities that distribute security tickets and control the access to resources and Tuple spaces in mobile environment. The proposed model presents good performance and is integrated to an e-health system: Relationship Management with Chronic Patient GRPC.