915 resultados para fixed telephony


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Wireless technologies are continuously evolving. Second generation cellular networks have gained worldwide acceptance. Wireless LANs are commonly deployed in corporations or university campuses, and their diffusion in public hotspots is growing. Third generation cellular systems are yet to affirm everywhere; still, there is an impressive amount of research ongoing for deploying beyond 3G systems. These new wireless technologies combine the characteristics of WLAN based and cellular networks to provide increased bandwidth. The common direction where all the efforts in wireless technologies are headed is towards an IP-based communication. Telephony services have been the killer application for cellular systems; their evolution to packet-switched networks is a natural path. Effective IP telephony signaling protocols, such as the Session Initiation Protocol (SIP) and the H 323 protocol are needed to establish IP-based telephony sessions. However, IP telephony is just one service example of IP-based communication. IP-based multimedia sessions are expected to become popular and offer a wider range of communication capabilities than pure telephony. In order to conjoin the advances of the future wireless technologies with the potential of IP-based multimedia communication, the next step would be to obtain ubiquitous communication capabilities. According to this vision, people must be able to communicate also when no support from an infrastructured network is available, needed or desired. In order to achieve ubiquitous communication, end devices must integrate all the capabilities necessary for IP-based distributed and decentralized communication. Such capabilities are currently missing. For example, it is not possible to utilize native IP telephony signaling protocols in a totally decentralized way. This dissertation presents a solution for deploying the SIP protocol in a decentralized fashion without support of infrastructure servers. The proposed solution is mainly designed to fit the needs of decentralized mobile environments, and can be applied to small scale ad-hoc networks or also bigger networks with hundreds of nodes. A framework allowing discovery of SIP users in ad-hoc networks and the establishment of SIP sessions among them, in a fully distributed and secure way, is described and evaluated. Security support allows ad-hoc users to authenticate the sender of a message, and to verify the integrity of a received message. The distributed session management framework has been extended in order to achieve interoperability with the Internet, and the native Internet applications. With limited extensions to the SIP protocol, we have designed and experimentally validated a SIP gateway allowing SIP signaling between ad-hoc networks with private addressing space and native SIP applications in the Internet. The design is completed by an application level relay that permits instant messaging sessions to be established in heterogeneous environments. The resulting framework constitutes a flexible and effective approach for the pervasive deployment of real time applications.

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[ES] El catalogar a un determinado bien o servicio como una de las «extensiones de los sentidos y las funciones humanas de la vista, el oído y el tacto», muestra la importancia del papel que desempeñan en nuestras vidas, muestra el desarrollo que alcanzaron impulsadas por las mismas necesidades de los seres humanos, muestra un mercado dinámico e importante. El servicio de telefonía móvil o celular es el desencadenador de estas expresiones y además tema de comentario, investigación y preocupación de comunidades científicas y organismos internacionales como el World Economic Forum de Davos.

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Esta dissertação examina as implicações do processo de acumulação de competências tecnológicas para a melhoria da performance técnico-econômica. Este relacionamento foi examinado na Telemar Norte Leste, empresa prestadora de serviços de telefonia fixa, durante o período de 1998 a 2002. O exame da acumulação de competências é feito tendo como base uma estrutura descritiva existente na literatura e adaptada especificamente para o setor de telefonia fixa. A aplicação de estruturas descritivas para examinar as implicações da acumulação de competências tecnológicas sobre o aprimoramento da performance técnico-econômica, em empresas do setor de telecomunicações no Brasil, ainda é escassa. Esta dissertação realiza essa análise, baseada num estudo de caso individual e fundamenta-se em evidências empíricas qualitativas e quantitativas, obtidas através de entrevistas, observação direta e documentação interna. A acumulação de competências tecnológicas foi estudada em duas funções: "desenvolvimento de processos comerciais, produtos e serviços" e "desenvolvimento de sistemas de telecomunicações e processos operacionais". O exame do aprimoramento de performance está baseado num conjunto de indicadores técnico-econômicos, típicos desse setor. A análise realizada na Telemar identificou que esta desenvolveu esforços que lhe possibilitaram acumular competências inovadoras nestas funções, considerando a estrutura analítica adaptada nesta dissertação, alcançando o Nível 5 ou Intermediário, numa escala de sete níveis. Foram ainda encontradas evidências de influencias positivas para o aprimoramento da performance de vinte e nove indicadores de desempenho analisados, representativos das funções analisadas. Alinhando-se a outros estudos recentes na literatura de empresas localizadas em países em desenvolvimento, as evidências encontradas nesta dissertação sugerem que a acumulação de competências para adaptar, modificar ou criar novas tecnologias é essencial para a sobrevivência e o desempenho competitivo das firmas, exercendo papel fundamental no aprimoramento de seus indicadores de performance. Outros fatores, internos e externos, podem também influenciar a evolução das empresas. Esta dissertação comenta somente a crise mundial do setor de telecomunicações. Provocada pela drástica reversão dos investimentos vinculados à nova economia, desde 2001 tem provocado uma revisão no processo de gestão dos prestadores de serviços de telecomunicações, afetando o desempenho organizacional. Este contexto, no entanto, dada a complexidade de suas implicações, não foram aqui examinados.

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Existe uma dissonância entre a teoria dominante de competição entre telefonias e evidências empíricas. Aquela tem como resultado que as redes de telefonia móvel irão definir a tarifa de interconexão abaixo do custo marginal de término da ligação. Já evidências empíricas diversas mostram que as tarifas de interconexão das telefonias móveis são mais elevadas e que as agências reguladoras encontram resistência destas ao aplicarem políticas de redução das tarifas de interconexão. Este trabalho desenvolve um modelo, baseado em Hoernig (2010), que provê resultados mais aderentes às evidências de existência de incentivos para precificação de tarifas de interconexão acima do custo marginal. O modelo aqui proposto inova em relação a Hoernig (2010) ao assumir que as redes de telefonia móvel concorrem com a telefonia fixa, a qual é sujeita à regulação da tarifa de interconexão. Esta é uma representação bastante plausível frente ao desenvolvimento da telefonia móvel. O modelo também considera o efeito de uma das empresas de telefonia móvel ter o seu controle compartilhado com a de telefonia fixa. Devido ao pressuposto de competição em um mesmo mercado entre telefonia fixa e móvel, é encontrado como resultado geral que as redes de telefonia móvel irão definir a tarifa de interconexão acima do custo marginal de término da ligação.

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A aproximação do término dos contratos de concessão do STFC demanda maior detalhamento das discussões acerca do modo de aplicação do instituto da reversibilidade de bens. Este artigo trata dos contornos da regra de reversão aplicável ao setor de telecomunicações, indicando os limites para e as ferramentas jurídicas para sua aplicação. Especificamente, postula-se que a Lei Geral de Telecomunicações e a Constituição Federal impossibilitam a adoção de uma leitura patrimonialista, sendo necessária a adoção de soluções contratuais com o propósito de viabilizar a reversão da posse dos bens reversíveis, em parcelas restritas àquelas estritamente indispensáveis à continuidade do STFC. The approaching term of the switched fixed telephony (STFC) concessions requires the discussions on asset reversibility to be held at a greater level of detail as to the characteristics of this legal concept. This paper outlines the asset reversibility rule applicable to the telecommunications sector and indicates the limits and legal tools for its implementation. Specifically, we argue that the Federal Constitution and the General Telecommunications Act do not allow for an interpretation centered on the estate in reversion (an interpretation we refer to as patrimonialista). Consequently, the implementation of this reversion rule should rely on contractual arrangements dealing with possessory rights over the assets which are essential for the continuous provision of STFC, or capacities thereof.

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In the last decade, mobile phones and mobile devices using mobile cellular telecommunication network connections have become ubiquitous. In several developed countries, the penetration of such devices has surpassed 100 percent. They facilitate communication and access to large quantities of data without the requirement of a fixed location or connection. Assuming mobile phones usually are in close proximity with the user, their cellular activities and locations are indicative of the user's activities and movements. As such, those cellular devices may be considered as a large scale distributed human activity sensing platform. This paper uses mobile operator telephony data to visualize the regional flows of people across the Republic of Ireland. In addition, the use of modified Markov chains for the ranking of significant regions of interest to mobile subscribers is investigated. Methodology is then presented which demonstrates how the ranking of significant regions of interest may be used to estimate national population, results of which are found to have strong correlation with census data.

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In this paper, a fixed-switching-frequency closed-loop modulation of a voltage-source inverter (VSI), upon the digital implementation of the modulation process, is analyzed and characterized. The sampling frequency of the digital processor is considered as an integer multiple of the modulation switching frequency. An expression for the determination of the modulation design parameter is developed for smooth modulation at a fixed switching frequency. The variation of the sampling frequency, switching frequency, and modulation index has been analyzed for the determination of the switching condition under closed loop. It is shown that the switching condition determined based on the continuous-time analysis of the closed-loop modulation will ensure smooth modulation upon the digital implementation of the modulation process. However, the stability properties need to be tested prior to digital implementation as they get deteriorated at smaller sampling frequencies. The closed-loop modulation index needs to be considered maximum while determining the design parameters for smooth modulation. In particular, a detailed analysis has been carried out by varying the control gain in the sliding-mode control of a two-level VSI. The proposed analysis of the closed-loop modulation of the VSI has been verified for the operation of a distribution static compensator. The theoretical results are validated experimentally on both single- and three-phase systems.

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Crest-fixed steel claddings made of thin, high strength steel often suffer from local pull-through failures at their screw connections during high wind events such as storms and hurricanes. Adequate design provisions are not available for these cladding systems except for the expensive testing provisions. Since the local pull-through failures in the less ductile steel claddings are initiated by transverse splitting at the fastener holes, numerical studies have not been able to determine the pull-through failure loads. Numerical studies could be used if a reliable splitting criterion is available. Therefore a series of two-span cladding and small scale tests was conducted on a range of crest-fixed steel cladding systems under simulated wind uplift loads. The strains in the sheeting around the critical central support screw fastener holes were measured until the pull-through failure occurred. This paper presents the details of the experimental investigation and the results including a strain criterion for the local pull-through failures in crest-fixed steel claddings.

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This paper examines the recent introduction of mobile telephony into rural communities in Papua New Guinea (PNG). It presents the findings of substantial fieldwork conducted in 2009, and suggests ways in which the new technology is already changing people’s lives and relationships. The paper identifies the roles of mobile telephones in two communities, the changes taking place and how villagers are responding to them. Comparison of the two villages is strategic as it highlights similarities in perceptions of mobile phones in these two very different settings. An ethnographic approach is adopted, situated within an interpretative methodology. Data collection methods include semi-structured interviews, orally-administered surveys and participant observation. The village lifestyle or ‘culture’ provides an important lens for understanding this data and the assertions made by village respondents. This research is significant as it addresses changes currently occurring in the communication methods of whole communities.