Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The Internet has experienced tremendous growth in the last three decades and has emerged as a platform to carryall forms of communications including voice, video and data. Along with this growth came the urgency for quality of service (QoS) controls in IP networks as different types of traffics have different service requirements. Although the IP protocol is able to scale to very large networks, it does not provide sufficient functionality for traffic engineering in order to enable QoS control. Multi-protocol label switching (MPLS) is a new routing technology that enhances IP with some QoS concepts from ATM and uses relatively simple packet forwarding mechanisms. MPLS has the ability to perform traffic engineering and QoS control by routing traffic flowson virtual connections called label switched paths (LSPs) which are assigned capacity. A large portion of the traffic carried on the Internet consists of data traffic in the form of TCP traffic. This thesis investigates several TCP models to find the ones most suitable to represent TCP traffic in MPLS networks. The models consist of three types. The first type models a single TCP source and the second type models a fixed number of TCP sources. The third type models an infinite number of TCP sources. The models were evaluated by comparing their throughput predictions and results obtained from simulation experiments that were done with the widely-used simulator ns. We also present a simple derivation of the 1/,;e law for the TCP congestion window size where e is the packet loss probability. / AFRIKAANSE OPSOMMING:In die afgelope drie dekades het die Internet beduidende groei ervaar, soveel so dat dit ontluik het as 'n medium om alle tipes van moderne kommunikasies te hanteer insluitend telefoon, video en data. Hierdie groei het gepaard gegaan met die behoefte na diensvlak (QoS) meganismes in IP netwerke aangesien verskillende tipe kommunikasies verskillende diens vereistes het. Alhoewel die IP protokol skalleerbaar is tot baie groot netwerke, voorsien dit nie voldoende funksionaliteit om QoS beheer toe te pas nie. "Multi-protocol label switching" (MPLS) is 'n nuwe roeterings tegnologie wat IP aanvul met QoS konsepte van ATM en dit maak gebruik van relatief eenvoudige pakkie versendings-meganismes. MPLS het die vermoe om netwerk-verkeer reeling en QoS beheer toe te pas deur verkeers-strome te roeteer op virtuele roetes genaamd "label switched paths" (LSPs) aan wie kapasiteit toegeken is. 'n Beduidende gedeelte van Internet-verkeer bestaan uit TCP-verkeer. Hierdie tesis ondersoek verskillende modelle van TCP om die te vind wat die mees geskik is om TCP verkeer in MPLS netwerke te verteenwoordig. Drie tipes modelle is ondersoek. Die eerste tipe moduleer 'n enkele TCP verkeersbron en die tweede tipe moduleer 'n vasgestelde aantal TCP verkeersbronne. Die derde tipe moduleer 'n oneindige aantal verkeersbronne. Die modelle is geevalueer deur hul voorspellings van die tempo van data transmissie te vergelyk met resultate van simulasies. Die simulasies is gedoen met die veelgebruikte simulator ns. Hierdie tesis bevat ook 'n eenvoudige afleiding vir die 1/,;e wet vir die TCP oorlading venster grootte met e die verlies waarskeinlikheid van 'n netwerk pakkie.

Data distribution management (DDM) is a mechanism to interconnect data producers and data consumers in a distributed application. Data producers provide useful data to consumers in the form of messages. For each message produced, DDM determines the set of data consumers interested in receiving the message and delivers it to those consumers. We are particularly interested in DDM techniques for parallel and distributed discrete event simulations. Thus far, researchers have treated synchronization of events (i.e. time management) and DDM independent of each other. This research focuses on how to realize time managed DDM mechanisms. The main reason for time-managed DDM is to ensure that changes in the routing of messages from producers to consumers occur in a correct sequence. Also time managed DDM avoids non-determinism in the federation execution, which may result in non-repeatable executions. An optimistic approach to time managed DDM is proposed where one allows DDM events to be processed out of time stamp order, but a detection and recovery procedure is used to recover from such errors. These mechanisms are tailored to the semantics of the DDM operations to ensure an efficient realization. A correctness proof is presented to verify the algorithm correctly synchronizes DDM events. We have developed a fully distributed implementation of the algorithm within the framework of the Georgia Tech Federated Simulation Development Kit (FDK) software. A performance evaluation of the synchronized DDM mechanism has been completed in a loosely coupled distributed system consisting of a network of workstations connected over a local area network (LAN). We compare time-managed versus unsynchronized DDM for two applications that exercise different mobility patterns: one based on a military simulation and a second utilizing a synthetic workload. The experiments and analysis illustrate that synchronized DDM performance depends on several factors: the simulations model (e.g. lookahead), applications mobility patterns and the network hardware (e.g. size of network buffers). Under certain mobility patterns, time-managed DDM is as efficient as unsynchronized DDM. There are also mobility patterns where time-managed DDM overheads become significant, and we show how they can be reduced.

With the emergence of computer networks as one of the primary platforms of communication, and with their adoption for an increasingly broad range of applications, there is a growing need for high-quality network traffic measurements to better understand, characterize and engineer the network behaviors. Due to the inherent lack of fine-grained measurement capabilities in the original design of the Internet, it does not have enough data or information to compute or even approximate some traffic statistics such as traffic matrices and per-link delay. While it is possible to infer these statistics from indirect aggregate measurements that are widely supported by network measurement devices (e.g., routers), how to obtain the best possible inferences is often a challenging research problem. We name this as "too little data" problem after its root cause. Interestingly, while "too little data" is clearly a problem, "too much data" is not a blessing either. With the rapid increase of network link speeds, even to keep sampled summarized network traffic (for inferring various network statistics) at low sample rates results in too much data to be stored, processed, and transmitted over measurement devices. In summary high-quality measurements in today's Internet is very challenging due to resource limitations and lack of built-in support, manifested as either "too little data" or "too much data". We present some new practices and proposals to alleviate these two problems.The contribution is four fold: i) designing universal methodologies towards ideal network traffic measurements; ii) providing accurate estimations for several critical traffic statistics guided by the proposed methodologies; iii) offering multiple useful and extensible building blocks which can be used to construct a universal network measurement system in the future; iv) leading to some notable mathematical results such as a new large deviation theorem that finds applications in various areas.

The growth of mobile networks and the imminent deployment of third generation networks and services will require signalling networks to maintain their integrity during increased unanticipated traffic volumes. As signalling networks become larger and more complex, an analysis ofprotocol operation is necessary to determine the effectiveness of the current protocol implementation and to evaluate the applicability of the proposed enhancements. The objective of this study ,is to develop analytical models to analyse the impact of Signalling Transfer Point congestion on network performance when simple message discard schemes are used as the primary flow control mechanism, and to investigate suitable congestion and flow control mechanisms to help alleviate the congestion. Unlike previous studies, that are localised and only concentrate on the nodes around the congested entity, the models presented here examine the impact of network wide and focused overloads on the entire network. The study considers both the fixed-line and mobile network environments, and analyses the performance of the ISDN User Part and Mobile Application Part protocols. The call completion rate and location update success rate are used to measure performance, instead of message throughput, since these parameters provide a more appropriate measure of the grade-of-service and more accurately reflect the level of service provided to a customer. The steady state equilibrium models, derived here, can be used to quickly estimate the safe operating regions of a signalling network, while the transient models provide a more intuitive perspective of the traffic processes that lead to congestion . Furthermore, these models can be used to examine the network performance for different message priority schemes, routing algorithms, overload scenarios and network configurations. The performance of various congestion control mechanisms that incorporate non-linear throttling schemes is also evaluated, together with an examination of the impact of congestion on multiple user parts in a mobile network environment. Message priority schemes are found to offer little or no advantage in a fixed network environment, but in a mobile network they can be used to maintain the network's performance at an optimum level during periods of overload. Network performance is also improved if congestion controls block load-generating traffic at the initial onset of congestion and then gradually restore traffic as the performance improves . / Thesis (Ph.D.)-University of Natal, Durban, 2002.

In this thesis, we analyze the bandwidth requirements of MPEG-4 AVC video traffic and then propose and evaluate the accuracy of new MPEG-4 AVC video traffic models. First, we analyze the bandwidth requirements of the videos by comparing the statistical characteristics of the different frame types. We analyze their coefficient of variability, autocorrelation, and crosscorrelation in both short and long term. The Hurst parameter is also used to investigate the long range dependence of the video traces. We then provide an insight into B-frame dropping and its impact on the statistical characteristics of the video trace. This leads us to design two algorithms that predict the size of the B-frame and the size of the group of pictures (GOP) in the short-term. To evaluate the accuracy of the prediction, a model for the error is proposed. In a broadband cable network, B-frame size prediction can be employed by a cable headend to provision video bandwidth efficiently or more importantly, reduce bit rate variability and bandwidth requirements via selective B-frame dropping, thereby minimizing buffering requirements and packet losses at the set top box. It will be shown that the model provides highly accurate prediction, in particular for movies encoded in high quality resolution. The GOP size prediction can be used to provision bandwidth. We then enhance the B-frame and GOP size prediction models using a new scene change detector metric. Finally, we design an algorithm that predicts the size of different frame types in the long-term. Clearly, a long-term prediction algorithm may suffer degraded prediction accuracy and the higher complexity may result in higher latency. However, this is offset by the additional time available for long-term prediction and the need to forecast bandwidth usage well ahead of time in order to minimize packet losses during periods of peak bandwidth demands. We also analyze the impact of the video quality and the video standard on the accuracy of the model.

Thesis (MSc (Mathematical Sciences. Computer Science))--University of Stellenbosch, 2008. / Consider a path-oriented telecommunications network where calls arrive to each route in a Poisson process. Each call brings on average a fixed number of packets that are offered to route. The packet inter-arrival times and the packet lengths are exponentially distributed. Each route can queue a finite number of packets while one packet is being transmitted. Each accepted packet/call generates an amount of revenue for the route manager. At specified time instants a route manager can acquire additional capacity (“interface capacity”) in order to carry more calls and/or the manager can acquire additional buffer space in order to carry more packets, in which cases the manager earns more revenue; alternatively a route manager can earn additional revenue by selling surplus interface capacity and/or by selling surplus buffer space to other route managers that (possibly temporarily) value it more highly. We present a method for efficiently computing the buying and the selling prices of buffer space. Moreover, we propose a bandwidth reallocation scheme capable of improving the network overall rate of earning revenue at both the call level and the packet level. Our reallocation scheme combines the Erlang price [4] and our proposed buffer space price (M/M/1/K prices) to reallocate interface capacity and buffer space among routes. The proposed scheme uses local rules and decides whether or not to adjust the interface capacity and/or the buffer space. Simulation results show that the reallocation scheme achieves good performance when applied to a fictitious network of 30-nodes and 46-links based on the geography of Europe.

O presente trabalho propõe uma arquitetura de controle de admissão de conexão para servidores de vídeo sob demanda, que visa introduzir garantias determinísticas para o atraso e aumentar a taxa de utilização do enlace. O sistema tira proveito do fato de que os arquivos de vídeo podem ser pré-processados, para calcular os parâmetros de tempo e espaço, com o objetivo de estimar a banda efetiva de um agregado de streams sobre o regime assintótico de muitas fontes. A geração automática dos arquivos de trace permite a caracterização total do processo de chegada dos dados, aumentando a precisão do cálculo da taxa de serviço requerida. Para contornar o problema de predição de tráfego, uma vez que o sistema não captura o comportamento dos fluxos de vídeo no domínio do tempo, o enlace é divido em vários enlaces virtuais, que transportam somente fluxos de vídeos idênticos. A utilização de um mecanismo, que compartilha a banda excedente, diminui o desperdício de recursos e a probabilidade de ocorrer uma violação aos parâmetros de QoS impostos. Todo processo de admissão de conexão é auxiliado por um sistema gestor de base de dados, onde uma função decide se deve ou não aceitar uma conexão pela simples comparação das somas das bandas efetivas das conexões com os recursos disponíveis. A eficiência do modelo proposto é analisada e comparada aos modelos determinísticos tradicionais. / This work proposes a admission control architecture for video-on-demand servers, which provide deterministic guarantees on the maximum delay of video traffic and increase the network resource utilization. The framework take advantage of the fact that stored video streams can be processed off-line to calculate the space and time parameters in order to estimate its effective bandwidth under the many sources asymptotic regime. The automatic generation of video data representation (packetized and encapsulated in network protocols) in textual format allows a full characterization of the underlying process so as to precisely calculate its bandwidth requirements. To bypass the traffic prediction problem, since the off-line estimation does not capture the exact dynamics of the video stream in the time domain, the link is divided into several virtual links, where only streams with same content are multiplexed (group multiplexing approach). The introduction of a borrowing mechanism to distribute the excess bandwidth to other groups which request service increases the resource utilization and QoS. The admission control is aided by a Database Management System, where a stored procedure decides whether to accept or reject a connection by simple compare the sum of effective bandwidths for the traffic streams with the available resources. The efficiency of the model is analyzed and compared with deterministic approachs.

Orientador: Leonardo de Souza Mendes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-14T09:31:29Z (GMT). No. of bitstreams: 1 Garcia_MarcosEduardoCoelho_M.pdf: 1970364 bytes, checksum: 9f8f5fa500e4831f5d7be68883a34f05 (MD5) Previous issue date: 2009 / Resumo: O comportamento de tráfegos VoIP em enlaces de rede é abordado neste trabalho. As aplicações VoIP possuem requisitos rígidos de Qualidade de Serviço (QoS) que devem ser previstos no projeto da rede. Neste sentido, é apresentado o Processo Poissoniano Modulado por Markov (MMPP) como um processo de chegadas adequado para caracterizar o comportamento de tráfegos VoIP sobrepostos. É levado em conta que as aplicações VoIP usam o mecanismo Supressão de Silêncio para economizar largura de banda, o que torna o tráfego muito variável e com chegadas em rajadas. Para análise do comportamento do enlace, é utilizado o modelo de fila MMPP/M/1. Para avaliar a viabilidade do modelo, foram feitos estudos comparativos com resultados do simulador ns-2. / Abstract: The behavior of VoIP traffic in network links is addressed in this work. VoIP applications have strict requirements for quality of service (QoS) that should be provided for in the network design. In this sense, the Markov Modulated Poisson Process (MMPP) is displayed as model of process of arrivals that is appropriate to characterize the behavior of superposition of VoIP traffic sources. It is taken into account that VoIP applications use the mechanism Suppression of Silence to save bandwidth, which makes the traffic very variable and with bursty arrivals. In order to analyze the behavior of the link, the MMPP/M/1 queue model is used. To evaluate the viability of the model, comparative studies were made with results of the ns-2 simulator. / Mestrado / Telecomunicações / Mestre em Engenharia Elétrica

Orientador: Lee Luan Ling / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T04:07:32Z (GMT). No. of bitstreams: 1 Stenico_JefersonWiliandeGodoy_D.pdf: 40438128 bytes, checksum: 1647243082abcfd8d16256d5f6027e53 (MD5) Previous issue date: 2014 / Resumo: Esta tese apresenta uma nova abordagem de construção de cascata multiplicativa, fundamentada na expressão do Binômio de Newton. Com base nessa nova cascata, é elaborado, um modelo de tráfego multifractal, denominado Modelo Multifractal baseado no Binômio de Newton - (MMBN). Esse modelo é capaz capturar com eficiência algumas das principais características multifractais observadas nas séries reais de tráfego estudadas via sua função escala e fator de momento. Expressões analíticas para a média e a variância do correspondente processo, foram derivadas, com a finalidade de obter uma modelagem mais precisa e robusta dos fluxos de tráfego de rede. Além disso, através da respectiva função autocorreção, foi demonstrado as características de dependência de longa duração (LDR). A avaliação de desempenho do novo modelo proposto foi avaliado utilizando as séries de tráfego reais provenientes de redes fixas e móveis wireless. Os resultados do desempenho foram comparados com outras abordagens multifractais bem conhecidas na literatura. Através dessa da análise, foi possível mostrar que o modelo de tráfego proposto é simples e capaz de representar com precisão as séries de tráfego com características multifractais. Baseado nessa nova abordagem de modelagem de tráfego, um parâmetro de escala global foi determinado e usado em conjunto com os parâmetros do modelo multifractal proposto, o que tornou possível a derivação de uma equação para a estimação de banda efetiva. O principal objetivo dessa expressão está em oferecer melhor alocação de recursos no planejamento e projetos de redes, especialmente para tráfegos com características multifractais. Outra novidade desta tese está na obtenção de uma expressão analítica geral para a estimação de probabilidade de perda para séries de tráfego com características multifractais, em um enlace com um único servidor e buffer finito. Para isso, foi utilizado o método de misturas de gaussianas para expressar a distribuição de cauda pesada do tráfego multifractal. A eficiência da modelagem estatística e a precisão da estimativa de probabilidade de perda foram validadas experimentalmente, assim como os resultados foram comparados com outros métodos multifractais, amplamente utilizados e conhecidos na literatura / Abstract: This thesis presents a novel construction scheme of multiplicative cascade, based on Newton Binomial expression. Based on this new cascade is established, also in an innovative way, a multifractal traffic model, called Multifractal Model based on Newton Binomial (MMNB). This model is able to faithfully capture some main characteristics of the multifractal processes, scaling function and moment factor. In order to get a more accurate and robust modeling of the networks traffic flows, we also derive analytical expressions for the mean and variance of the corresponding network traffic process and show that its autocorrelation function exhibits long-range dependent characteristics (LRD). The performance evaluation of our model has been evaluated using real traffic traces from fixed and mobile networks. The results were compared with those provided by other well-known traffic models reported in the literature. We show that the proposed model is simple and capable of accurately representing network traffic traces with multifractal characteristics. Based on a new approach for traffic modeling and the corresponding multifractal traffic parameters, a global scaling parameter is determined and used together with the multifractal traffic model parameters for the effective bandwidth computation in order to offer better resource allocation in network planning and design, especially for network traffic with multifractal characteristics. Another novel contribution of this thesis is the derivation of a general analytical expression for the loss probability for traffic traces with multifractal characteristics in queuing systems with a simple server and finite buffer. For this, we used Gaussian mixture model to express the heavy tail distribution, one of the most important properties of multifractal traffic. The efficiency of this statistical model and the accuracy of the estimated loss probabilities are experimentally validated by a comparison with other multifractal approaches widely used and well-known in the literature / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

Orientador: Lee Luan Ling / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-04T02:56:17Z (GMT). No. of bitstreams: 1 Pereira_TatianaBrito_M.pdf: 2502862 bytes, checksum: 4f913e9451b6cbf542c6f1335b1619d8 (MD5) Previous issue date: 2004 / Resumo: O crescimento explosivo e a natureza heterogênea da Internet demandam ferramentas ¿inteligentes¿ que permitam aos protocolos de roteamento adaptarem-se à situação corrente da rede (topologia e situação de congestionamento). Ferramentas inteligentes, porém, significam, na maioria das vezes, grande sobrecarga de processamento e comunicação. O presente trabalho apresenta, além de uma nova estratégia de roteamento OSPF adaptativo baseado em estimação de banda, uma plataforma de simulação capaz de expor o desempenho de uma rede de interconexão submetida (ou não) a esta nova estratégia. A avaliação de desempenho é realizada graças a um modelo, desenvolvido no simulador OPNET, que adiciona ao modelo de um roteador os módulos para estimação de banda e atualização de custos. Os módulos (de estimação de banda e de atualização de custo) adicionados permitem que o protocolo OSPF tome suas decisões de roteamento baseando-se nas condições de congestionamento da rede e nos índices de qualidade desejados para os enlaces. Neste ambiente de simulação, a topologia da rede é representada por um grafo e o tráfego, a que estará sujeita a rede, durante o período de simulação, é especificado por funções de distribuição que atuam durante um intervalo determinado em um roteador específico da rede. A possibilidade de se estabelecer diversas funções de geração de tráfego, atuando a partir de diversos pontos da rede em intervalos independentes, garante certa representação do dinamismo do tráfego encontrado nas redes atuais. Como resultado das simulações, temos uma análise do impacto desta estratégia adaptativa em parâmetros de desempenho de rede, em comparação com o impacto do roteamento OSPF tradicional / Abstract: Internet increase and diversity demand ¿smart¿ tools that could make possible to routing protocols self-adapt to network current state (its topology and congestion situation). Smart tools, although, can result in great processing and communication overload. This work presents, besides a new adaptive OSPF routing strategy based on bandwidth estimations, a simulation platform able to expose results of network performance while experimenting (or not) the proposed adaptive routing strategy. The performance analysis is accomplished due to a model, developed in OPNET network simulator, that adds to a router model modules to bandwidth estimation and link cost updating. These additional modules allow OSPF protocol to take its routing decisions based on network link conditions and on desired link qualities. Network topology is represented by a graph and the traffic presented during simulation is specified by distribution functions acting in specific routers during established intervals. The possibility of configuring various traffic generation functions, acting from various network points in independent intervals, ensures certain network traffic dynamic representation. The simulation results offer an analysis of the proposed OSPF adaptive routing strategy, in comparison to the conventional OSPF routing, in terms of network performance parameters / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica