Página 1 dos resultados de 8857 itens digitais encontrados em 0.013 segundos

Alocação dinâmica de largura de banda em redes EPON; Dynamic bandwidth allocation for EPON networks

Carrasco Arbieto, Carmen Orencia
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 10/08/2007 PT
Relevância na Pesquisa
36.83%
As redes de telecomunicações se dividem em redes de longa distância, redes metropolitanas e redes de acesso. As redes de longa distância e metropolitana usufruem a alta capacidade de largura de banda da fibra óptica, enquanto nas redes de acesso há um gargalo de largura de banda por causa do uso de pares de fios e cabo coaxial. Para solucionar este problema e oferecer aos usuários acesso banda larga de baixo custo foram propostas as redes ópticas passivas (passive optical network - PON). A PON é formada por dois elementos básicos, a unidade de rede óptica (optical network unit - ONU), localizada perto dos assinantes, e o terminal de linha óptica (optical line terminal - OLT), localizado próximo ao provedor de serviços. Dentre os padrões disponíveis para redes PON, o Ethernet (EPON), padronizado pelo grupo IEEE 802.3ah, é opção atraente porque ele é bastante difundido nas redes locais. O protocolo de controle multiponto (multipoint control protocol - MPCP), já especificado, é responsável pelo controle de acesso ao meio, fornecendo infra-estrutura de sinalização para transmissão entre OLT e ONUs. Entretanto, o algoritmo de alocação de largura de banda, que realiza o controle de acesso ao meio com base no MPCP...

Algoritmo de alocação dinâmica de largura de faixa para redes de comunicação móvel celular; Dynamic bandwidth allocation algorithm for mobile communication networks

Queiroz, Eduardo Martinelli Galvão de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/03/2008 PT
Relevância na Pesquisa
36.91%
O crescente aumento da demanda de tráfego nas redes celulares vem aumentando a necessidade de uma melhor utilização dos recursos do sistema, já que sua expansão é custosa. Nas estações rádio base (ERB), a disponibilidade de largura de faixa de freqüências é limitada e desta maneira, em uma rede de comunicação móvel celular, o controle de admissão de chamadas exerce grande influência no desempenho do sistema, pois determina a utilização de banda das ERBs e se uma determinada quantidade de recursos (banda) será alocado ou não para uma determinada chamada. O desempenho da rede pode ser atrelado a determinados parâmetros, como a probabilidade de bloqueio de novas chamadas, probabilidade de bloqueio de chamadas handoff e a utilização de banda da rede. Este trabalho propõe um controle de admissão de chamadas que, no atendimento de uma chamada, faz o empréstimo de banda de chamadas em andamento na célula no caso de banda insuficiente. O sistema adota um mecanismo heurístico que determina a banda disponível para novas chamadas conforme os valores de certos parâmetros do sistema. O empréstimo de banda é realizado em chamadas em andamento nas células até níveis mínimos estabelecidos para cada tipo de chamada...

Algoritmos para alocação de banda em redes de acesso GPON; Algorithms for bandwidth allocation in GPON access networks

Santos, Alex Ferreira dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/02/2010 PT
Relevância na Pesquisa
36.89%
Neste trabalho propomos e analisamos algoritmos de alocação dinâmica de banda para rede óptica passiva (PON) de acesso padrão GPON (Gigabit PON). Estes algoritmos utilizam dados oriundos de SLA (service level agreement) para gerenciar a alocação de banda e classificar em 4 contêineres de tráfego (T-CONT) o tráfego gerado em 16 ONUs (optical network unit). Na transmissão upstream é utilizada a técnica de multiplexação por divisão de tempo (TDM) para gerenciar o acesso ao meio, evitando colisões. O primeiro algoritmo proposto aloca banda garantida para as ONUs e distribui a banda não utilizada de acordo com critério baseado em três SLAs. A taxa de bit upstream é 1,25 Gbps e o desempenho do algoritmo é analisado com base na variação do atraso de pacotes em função do tráfego gerado nas ONUs. O segundo algoritmo proposto utiliza ponderação de tráfego. Neste, analisamos o comportamento dos atrasos e a quantidade de banda solicitada e atendida por ONU quando as bandas garantida e extra são alteradas. Por fim, acrescentamos em nossa implementação um intervalo para o processamento do algoritmo de alocação dinâmica de banda (DBA) e resposta do hardware relacionado ao ciclo de interrogação. Então, analisamos o atraso de pacotes quando variamos o intervalo de processamento do DBA. Ao final...

Contribuições ao calculo de banda e de probabilidade de perda para trafego multifractal de redes; Contributions to the effective bandwidth and loss probability computing for multifractal network traffic

Flavio Henrique Teles Vieira
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/12/2006 PT
Relevância na Pesquisa
36.91%
A modelagem multifractal generaliza os modelos de tráfego existentes na literatura e se mostra apropriada para descrever as características encontradas nos fluxos de tráfego das redes atuais. A presente tese investiga abordagens para alocação de banda, predição de tráfego e estimação de probabilidade de perda de bytes considerando as características multifractais de tráfego. Primeiramente, um Modelo Multifractal baseado em Wavelets (MMW) é proposto. Levando em consideração as propriedades deste modelo, são derivados o parâmetro de escala global, a função de autocorrelação e a banda efetiva para processos multifractais. A capacidade de atualização em tempo real do MMW aliada à banda efetiva proposta permite o desenvolvimento de um algoritmo de estimação adaptativa de banda efetiva. Através deste algoritmo é introduzido um esquema de provisão adaptativo de banda efetiva. Estuda-se também a alocação de banda baseada em predição de tráfego. Para este fim, propõe-se um preditor adaptativo fuzzy de tráfego, o qual é aplicado em uma nova estratégia de alocação de banda. O preditor fuzzy adaptativo proposto utiliza funções de base ortonormais baseadas nas propriedades do MMW. Com relação à probabilidade de perda para tráfego multifractal...

Estudo de trafego e alocação de banda para redes multiserviço; Traffic study and bandwidth allocation for multservice networks

Firmiano Ramos Perlingeiro
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 18/12/2006 PT
Relevância na Pesquisa
36.72%
O provisionamento de QoS garantida é de extrema importância no desenvolvimento das futuras redes. Os recentes avanços tecnológicos em comutação e em transmissão permitem a implementação de redes com velocidades extremamente altas que podem transportar grandes quantidades de tráfego geradas por aplicações mais sensíveis aos requisitos de qualidade de serviço. A próxima geração de redes deverá suportar novas aplicações multimídia em um ambiente global e disponibilizar novos serviços em plataformas flexíveis sem necessidade de alteração da infra-estrutura. Isto requer uma nova arquitetura de redes capaz de oferecer serviços de transporte e de processamento para aplicações de comunicação com fortes requisitos de QoS. No amplo escopo da engenharia de tráfego de redes e do provimento de serviços com qualidade assegurada, esta tese se dedica a propor algumas soluções para os problemas de alocação de recursos de rede, em especial soluções para a estimação da banda efetiva. Para tanto, se utiliza de forma intensiva a caracterização de tráfego, métodos analíticos, heurísticos e de simulação. Os métodos propostos de alocação de banda neste estudo estão fundamentados na Teoria dos Grandes Desvios...

Bandwidth aspects in second generation current conveyors

Alves, L. N.; Aguiar, R.L.; Santos, D.M.
Fonte: Springer Verlag Publicador: Springer Verlag
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.83%
This paper discusses bandwidth problems associated with second-generation current conveyors (CCII). In particular, our work is centered in high-capacitance applications, and has been oriented for wireless optical links and applied physics. We discuss techniques for improving bandwidth in these CCIIs, and develop a new CCII structure with larger bandwidth than traditional circuits. These circuits are then compared in terms of their noise and dynamic range characteristics. A test circuit was developed to verify these different bandwidth behaviors.

Bandwidth boosting in transimpedance amplifiers for optical LANs, using delayed feedback

Martins, N.; Barbosa, L.; Alves, L. N.; Aguiar, R.L.
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
36.72%
Delayed-feedback amplifiers are composed of, a forward gain amplifier, a feedback network and a time-delay element. Recently published results [1] claim the possibility of bandwidth enhancement for this type of systems, simply by a judicious choice of loop-gain, open loop poles and the net time-delay. This paper describes the design steps for a shunt-shunt feedback amplifier with an active delay on the feedback loop. The designed circuit was optimized for Free-Space Optical (FSO) line-of-sight receivers. Achieved results show that the inclusion of the active delay, improve bandwidth in a maximum of 60%. A maximum of 1.5THzΩ. GBW (11kΩ. transimpedance gain) was achieved with a photodiode having intrinsic capacitance of 100pF.

Maximizing bandwidth in CCII for wireless optical applications

Alves, L. N.; Aguiar, R.L.
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
36.89%
This paper discusses bandwidth problems associated with the usage of second-generation current conveyors in wireless optical systems, and presents a new current amplifier with wide bandwidth and large input dynamic range, developed for Fast Ethernet wireless applications This current amplifier is used to interconnect low cost photo-detectors (with large intrinsic capacitance) with transimpedance amplifiers, overcoming typical bandwidth limitations imposed by the input transducers. This current adaptation concept has proved to be adequate for increasing both bandwidth and dynamic range of traditional optical interfaces. The proposed current amplifier architecture is based on a CCII with reduced input impedance and achieves, for a lOpF input photo detector, a maximum gain of 18dB with a 130MHz bandwidth, with a noise floor of 9.2pA/√Hz,. The expected input dynamic range is larger than 65dB. © 2001 IEEE.

Bandwidth aspects in second generation current conveyors

Alves, Luis Nero; Aguiar, Rui L.; Santos, Dinis M.
Fonte: Faculdade de Engenharia da Universidade do Porto Publicador: Faculdade de Engenharia da Universidade do Porto
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
36.72%
This paper discusses bandwidth problems associated with second–generation current conveyors. In particular, our work is centered in high-capacitance applications, especially for wireless optical links and applied physics. We discuss techniques for improving bandwidth in these CCII, and develop a new CCII structure with larger bandwidth than traditional circuits. These circuits are then compared in terms of their noise and dynamic range characteristics.

Limits to Certainty in QoS Pricing and Bandwidth

Gideon, Carolyn; Camp, L. Jean
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 46353 bytes; application/pdf
EN_US
Relevância na Pesquisa
36.89%
This paper explores the relationship between certainty of bandwidth and certainty of price for Internet services over a statistically shared network. Both are important policy objectives. Certainty of bandwidth is necessary if the Internet is to serve as a platform for advanced communications, information and entertainment services, or even for telephony. Certainty of price is important for universal service. More specifically, we illustrate that certainty of bandwidth and certainty of price are mutually exclusive in a statistically shared network (of which the Internet is the canonical example). Section 2 of this paper outlines the importance of certainty of price and how it might be achieved. Section 3 explains the importance of certainty in bandwidth and how different QoS protocols impact variations in bandwidth. Here, we use standard queuing models to show that increasing certainty in bandwidth results in decreased certainty in price. Conversely, setting a constant price with cost-based pricing in a statistically shared network results in delay. This is followed by a discussion of market evidence for this inverse relationship between certainty of price and certainty of bandwidth. Finally, we present conclusions and implications to be considered by policy makers.

Can High Bandwidth and Latency Justify Large Cache Blocks in Scalable Multiprocessors?

LeBlanc, Thomas J. ; Bianchini, Ricardo
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Relatório
ENG
Relevância na Pesquisa
36.86%
An important architectural design decision affecting the performance of coherent caches in shared-memory multiprocessors is the choice of block size. There are two primary factors that influence this choice: the reference behavior of application programs and the remote access bandwidth and latency of the machine. Several studies have shown that increasing the block size can lower the miss rate and reduce the number of invalidations. However, increasing the block size can also increase the miss rate by, for example, increasing false sharing or the number of cache evictions. Large cache blocks can also generate network contention. Given that we anticipate enormous increases in both network bandwidth and latency in large-scale, shared-memory multiprocessors, the question arises as to what effect these increases will have on the choice of block size. We use analytical modeling and execution-driven simulation of parallel programs on a large-scale shared-memory machine to examine the relationship between cache block size and application performance as a function of remote access bandwidth and latency. We show that even under assumptions of high remote access bandwidth, the best application performance usually results from using cache blocks between 32 and 128 bytes in size. Using even larger blocks tends to increase the mean cost per reference...

Exploiting Bandwidth to Reduce Average Memory Access Time in Scalable Multiprocessors

Bianchini, Ricardo ; LeBlanc, Thomas J.
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Technical Report; Thesis
ENG
Relevância na Pesquisa
36.78%
Thesis (Ph. D.)--University of Rochester. Dept. of Computer Science, 1995. Simultaneously published in the Technical Report series.; The overhead of remote memory accesses is a major impediment to achieving good application performance on scalable shared-memory multiprocessors. This dissertation explores ways in which to exploit network and memory bandwidth in order to reduce the average cost of memory accesses. We consider scenarios in which (1) the remote access cost is dominated by contention, and (2) the hardware provides abundant bandwidth and the remote access time is dominated by the unsaturated request/access/reply sequence of operations. We introduce and evaluate two techniques for increasing the effective bandwidth available to processors, software interleaving and eager combining. We also evaluate strategies for hiding the high cost of remote accesses, including several forms of prefetching and update-based coherence protocols. We use both analytic models and detailed simulations of multiprocessor systems to quantify the effectiveness of these techniques, and to provide insight into the potential and limitations of exploiting bandwidth to reduce average memory access cost.

Uma avaliação de heurísticas para redução de largura de banda de matrizes; An evaluation of heuristics for matrix bandwidth reduction

Chagas, Guilherme Oliveira
Fonte: Programa de Pós-Graduação em Ciência da Computação; UFLA; brasil; Departamento de Ciência da Computação Publicador: Programa de Pós-Graduação em Ciência da Computação; UFLA; brasil; Departamento de Ciência da Computação
Tipo: Dissertação
Publicado em 27/08/2015 POR
Relevância na Pesquisa
36.78%
Computational cost of a linear system solver can be reduced by matrix bandwidth reduction. Bandwidth reduction consists of carrying out permutations of lines and columns so that they allow coefficients to remain near the main diagonal. By a systematic review, eight heuristics were identified with the best benefits, i.e., bandwidth reduction per computational cost, and then were implemented. In addition, the GPS heuristic, one of the most known heuristic in this problem, was implemented. Furthermore, two new heuristics are proposed in this work. Computational simulations were performed with these 11 heuristics in 113 instances of the Harwell-Boeing Sparse Matrix Collection and with three sets of instances with linear systems obtained from discretizations of the heat conduction and the Laplace equations by finite volumes. These linear systems were solved using the preconditioned Conjugate Gradient Method. According to the results presented here, the best heuristic in the simulations performed with the Harwell-Boeing Sparse Matrix Collection was the Variable neighborhood search for bandwidth reduction. However, this heuristic is not indicated to reduce the computational cost of preconditioned Conjugate Gradient Method in large-scale sparse linear systems. In particular...

PathChirp: Efficient Available Bandwidth Estimation for Network Paths

Ribeiro, Vinay Joseph; Riedi, Rudolf H.; Baraniuk, Richard G.; Navratil, Jiri; Cottrell, Les; Ribeiro, Vinay Joseph; Riedi, Rudolf H.; Baraniuk, Richard G.; Navratil, Jiri; Cottrell, Les
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
ENG
Relevância na Pesquisa
36.78%
Conference Paper; This paper presents PathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of "self-induced congestion," PathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing rate within each chirp, PathChirp obtains a rich set of information from which to dynamically estimate the available bandwidth. Since it uses only packet interarrival times for estimation, PathChirp does not require synchronous nor highly stable clocks at the sender and receiver. We test PathChirp with simulations and Internet experiments and find that it provides good estimates of the available bandwidth while using up to an order-of-magnitude fewer bytes than current state-of-the-art techniques.

Locating Available Bandwidth Bottlenecks

Ribeiro, Vinay Joseph; Riedi, Rudolf H.; Baraniuk, Richard G.; Ribeiro, Vinay Joseph; Riedi, Rudolf H.; Baraniuk, Richard G.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.72%
Journal Paper; The Spatio-temporal Available Bandwidth estimator (STAB), a new edge-based probing tool, locates thin links --- those links with less available bandwidth than all links preceeding them --- on end-to-end network paths. By localizing thin links, STAB facilitates network operations and troubleshooting, provides insight into what causes network congestion, and aids network-aware applications. The tool uses special chirp probing trains, featuring an exponential flight pattern of packets, which have the advantage of employing few packets while giving an accurate estimate of available bandwidth.

Local Cross-validation for Spectrum Bandwidth Choice

Velasco, Carlos
Fonte: Blackwell Publicador: Blackwell
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em /05/2000 ENG
Relevância na Pesquisa
36.72%
We investigate an automatic method of determining a local bandwidth for non-parametric kernel spectral density estimates at a single frequency. This procedure is a modification of a cross-validation technique for global bandwidth choices, avoiding the computation of any pilot estimate based on initial bandwidths or on approximate parametric models. Only local conditions on the spectral density around the frequency of interest are assumed. We illustrate with a Monte Carlo study the performance in finite samples of the bandwidth estimates proposed.

Impact of transient CSMA/CA access delays on active bandwidth measurements

Portoles-Comeras, Marc; Cabellos-Aparicio, Albert; Mangues-Bafalluy, Josep; Banchs, Albert; Domingo- Pascual, Jordi
Fonte: ACM Publicador: ACM
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/conferenceObject Formato: application/pdf
Publicado em //2009 ENG
Relevância na Pesquisa
36.78%
WLAN devices based on CSMA/CA access schemes have become a fundamental component of network deployments. In such wireless scenarios, traditional networking applications, tools, and protocols, with their built-in measurement techniques, are usually run unchanged. However, their actual interaction with the dynamics of underlying wireless systems is not yet fully understood. A relevant example of such built-in techniques is bandwidth measurement. When considering WLAN environments, various preliminary studies have shown that the application of results obtained in wired setups is not straightforward. Indeed, the contention for medium sharing among multiple users inherent to CSMA/CA access schemes has remarkable consequences on the behavior of and results obtained by bandwidth measurement techniques. In this paper, we focus on evaluating the effect of CSMA/CA-based contention on active bandwidth measurement techniques. As a result, it presents the rate response curve in steady state of a system with both FIFO and CSMA/CA-based contending cross-traffic. We also find out that the distribution of access delay shows a transient regime before reaching a stationary state. The duration of such transient regime is characterized and bounded. We also show how dispersion-based measurements that use a short number of probing packets are biased measurements of the achievable throughput...

A FRAMEWORK FOR EFFICIENT BANDWIDTH MANAGEMENT IN BROADBAND WIRELESS ACCESS SYSTEMS

Al-Manthari, Bader
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 1864297 bytes; application/pdf
EN; EN
Relevância na Pesquisa
36.97%
Broadband Wireless Access Systems (BWASs) such as High Speed Downlink Packet Access (HSDPA) and the Worldwide Interoperability for Microwave Access (WiMAX), pose a myriad of new opportunities for leveraging the support of a wide range of “content-rich” mobile multimedia services with diverse Quality of Service (QoS) requirements. This is due to the remarkably high bandwidth that is supported by these systems, which was previously only available to wireline connections. Despite the support for such high bandwidth, satisfying the diverse QoS of users while maximizing the revenues of network operators is still one of the major issues in these systems. Bandwidth management, therefore, will play a decisive role in the success of such wireless access systems. Without efficient bandwidth management, network operators may not be able to meet the growing demand of users for multimedia services, and may consequently suffer great revenue loss. Bandwidth management in BWASs is, however, a challenging problem due to many issues that need to be taken into consideration. Examples of such issues include the diverse QoS requirements of the services that BWASs support, the varying channel quality conditions of mobile users, and hence the varying amount of resources that are needed to guarantee certain QoS levels during the lifetime of user connections...

General model for delayed feedback and its application to transimpedance amplifier's bandwidth optimization

Alves, L. N.; Barbosa, L.; Macedo, E.A.L.; Aguiar, R.L.
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
36.78%
Delays in real systems can be of two types: i) intrinsic delays - due to the physical principles of operation of each electronic device; ii) designed delays - due to extra circuits used to add the desired delay. Previous work established the possibility of achieving bandwidth improvements using small delays inside the feedback loop of feedback amplifiers. The modeling approach followed on these contributions used only one designed delay element. The bandwidth reduction effect due to intrinsic delays was not considered on these contributions. This paper extends the concept to the general case of feedback amplifiers that incorporates delays of both types. An experimental demonstration using a simple 0.35μm BiCMOS transimpedance amplifier further confirms the proposed model. © 2006 IEEE.

Bandwidth choice for local polynomial estimation of smooth boundaries

Hall, Peter; Park, B
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.91%
Local polynomial methods hold considerable promise for boundary estimation, where they offer unmatched flexibility and adaptivity. Most rival techniques provide only a single order of approximation; local polynomial approaches allow any order desired. Their more conventional rivals, for example high-order kernel methods in the context of regression, do not have attractive versions in the case of boundary estimation. However, the adoption of local polynomial methods for boundary estimation is inhibited by lack of knowledge about their properties, in particular about the manner in which they are influenced by bandwidth; and by the absence of techniques for empirical bandwidth choice. In the present paper we detail the way in which bandwidth selection determines mean squared error of local polynomial boundary estimators, showing that it is substantially more complex than in regression settings. For example, asymptotic formulae for bias and variance contributions to mean squared error no longer decompose into monotone functions of bandwidth. Nevertheless, once these properties are understood, relatively simple empirical bandwidth selection methods can be developed. We suggest a new approach to both local and global bandwidth choice, and describe its properties.