Estimation of traf- fic matrices in the presence of long memory traffic

The estimation of traffic matrices in a communications network on the basis of a set of traffic measurements on the network links is a well-known problem, for which a number of solutions have been proposed when the traffic does not show dependence over time, as in the case of the Poisson process. However, extensive measurements campaigns conducted on IP networks have shown that the traffic exhibits long range dependence. Here a method is proposed for the estimation of traffic matrices in the case of long range dependence, and its theoretical properties are studied. Its merits are then evaluated via a simulation study. Finally, an application to real data is provided

Aspects of proactive traffic engineering in IP networks

To deliver a reliable communication service over the Internet it is essential for the network operator to manage the traffic situation in the network. The traffic situation is controlled by the routing function which determines what path traffic follows from source to destination. Current practices for setting routing parameters in IP networks are designed to be simple to manage. This can lead to congestion in parts of the network while other parts of the network are far from fully utilized. In this thesis we explore issues related to optimization of the routing function to balance load in the network and efficiently deliver a reliable communication service to the users. The optimization takes into account not only the traffic situation under normal operational conditions, but also traffic situations that appear under a wide variety of circumstances deviating from the nominal case. In order to balance load in the network knowledge of the traffic situations is needed. Consequently, in this thesis we investigate methods for efficient derivation of the traffic situation. The derivation is based on estimation of traffic demands from link load measurements. The advantage of using link load measurements is that they are easily obtained and consist of a limited amount of data that need to be processed. We evaluate and demonstrate how estimation based on link counts gives the operator a fast and accurate description of the traffic demands. For the evaluation we have access to a unique data set of complete traffic demands from an operational IP backbone. However, to honor service level agreements at all times the variability of the traffic needs to be accounted for in the load balancing. In addition, optimization techniques are often sensitive to errors and variations in input data. Hence, when an optimized routing setting is subjected to real traffic demands in the network, performance often deviate from what can be anticipated from the optimization. Thus, we identify and model different traffic uncertainties and describe how the routing setting can be optimized, not only for a nominal case, but for a wide range of different traffic situations that might appear in the network. Our results can be applied in MPLS enabled networks as well as in networks using link state routing protocols such as the widely used OSPF and IS-IS protocols. Only minor changes may be needed in current networks to implement our algorithms. The contributions of this thesis is that we: demonstrate that it is possible to estimate the traffic matrix with acceptable precision, and we develop methods and models for common traffic uncertainties to account for these uncertainties in the optimization of the routing configuration. In addition, we identify important properties in the structure of the traffic to successfully balance uncertain and varying traffic demands

Análise estatística e modelação de redes óticas de transporte

Doutoramento em TelecomunicaçõesStatistical analysis and modeling of networks is now an integral part of network science and engineering. In case of optical transport networks (OTNs), it can be used for the planning and dimensioning when the complete information is not available or is difficult to process. The core networks around the world today are almost optical and they form the backbone of the Internet. Therefore, the statistical characteristics of these networks must be studied to understand their nature and to estimate their parameters. In science and technology, network analysis and modeling are used for several purposes such as the analysis of their stability, reliability and long term evolution. Knowledge of the statistical models helps in the estimation of several critical parameters of the networks. The work presented in this thesis is focused on the analysis and modeling of link lengths and shortest path lengths in OTNs. The parameters used in the models presented in this thesis can be estimated from the very basic information of the networks such as the coverage area and the number of nodes, both of which can be found from the node locations. These models can be applied to estimate key parameters of the networks. In this thesis, we have shown that the link lengths of the OTNs follow general extreme value distribution. The parameters of the proposed distribution can be estimated from the average link lengths of the networks. We develop expressions for the average link lengths of OTNs which can be estimated with an average error of just 11%. We apply the developed model to estimate link length dependent parameters in OTNs. We show that the shortest path lengths of the OTNs follow Johnson SB distribution. We estimate the parameters of the developed model from the convex area and the number of nodes of the network. We also apply this model to estimate several shortest path-dependent parameters in OTNs.A análise estatística e modelação de redes é atualmente uma parte integrante da ciência e engenharia de redes. No caso das redes óticas de transporte (OTN), a modelação estatistica pode ser usada para o planeamento e dimensionamento quando a informação completa não está disponível ou o seu processamento é muito demorado. As redes óticas constituem atualmente o núcleo central das redes que suportam a Internet. Portanto, as características estatísticas dessas redes devem ser estudadas por forma a compreender sua natureza e estimar os seus parâmetros. Em ciência e tecnologia, a análise e modelação de redes é usada para vários fins, tais como análise de estabilidade, fiabilidade e evolução a longo prazo. O conhecimento dos modelos estatísticos ajuda na estimativa de vários parâmetros críticos das redes. O trabalho apresentado nesta tese está focado na análise e modelação dos comprimentos das ligaçães e dos caminhos mais curtos em OTN. Os parâmetros usados nos modelos apresentados nesta tese podem ser estimados a partir de informação muito simples das redes, tais como a sua área de cobertura e o número de nós, sendo que ambas podem ser obtidas a partir da localização dos nós. Estes modelos podem ser aplicados para estimar parâmetros-chave das redes. Nesta tese, demonstramos que o comprimento dos ligações em OTN segue uma distribuição do tipo general extreme value. Os parâmetros da distribuição podem ser estimados a partir do comprimento médio das ligações. Por sua vez mostramos que o comprimento médio das ligações pode ser estimado com um erro médio de 11% sendo apenas conhecida a área de cobertura da rede. Mostramos como é possivel aplicar o modelo desenvolvido à estimação de parâmetros dependentes do comprimento das ligações. Mostramos também que o comprimento dos caminhos mais curtos segue uma distribuição do tipo Johnson SB. Os parâmetros usados neste modelo podem ser estimados a partir da área convexa e do número de nós da rede. Aplicamos ainda este modelo para estimar diversos parâmetros dependentes do caminho mais curto

Supporting NAT traversal and secure communications in a protocol implementation framework

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Electrotécnica e de ComputadoresThe DOORS framework is a versatile, lightweight message-based framework developed in ANSI C++. It builds upon research experience and subsequent knowledge garnered from the use and development of CVOPS and OVOPS, two well known protocol development frameworks that have obtained widespread acceptance and use in both the Finnish industry and academia. It conceptually resides between the operating system and the application, and provides a uniform development environment shielding the developer from operating system speci c issues. It can be used for developing network services, ranging from simple socket-based systems, to protocol implementations, to CORBA-based applications and object-based gateways. Originally, DOORS was conceived as a natural extension from the OVOPS framework to support generic event-based, distributed and client-server network applications. However, DOORS since then has evolved as a platform-level middleware solution for researching the provision of converged services to both packet-based and telecommunications networks, enterprise-level integration and interoperability in future networks, as well as studying application development, multi-casting and service discovery protocols in heterogeneous IPv6 networks. In this thesis, two aspects of development work with DOORS take place. The rst is the investigation of the Network Address Translation (NAT) traversal problem to give support to applications in the DOORS framework that are residing in private IP networks to interwork with those in public IP networks. For this matter this rst part focuses on the development of a client in the DOORS framework for the Session Traversal Utilities for NAT (STUN) protocol, to be used for IP communications behind a NAT. The second aspect involves secure communications. Application protocols in communication networks are easily intercepted and need security in various layers. For this matter the second part focuses on the investigation and development of a technique in the DOORS framework to support the Transport Layer Security (TLS) protocol, giving the ability to application protocols to rely on secure transport layer services

Congestion detection within multi-service TCP/IP networks using wavelets.

Using passive observation within the multi-service TCP/IP networking domain, we have developed a methodology that associates the frequency composition of composite traffic signals with the packet transmission mechanisms of TCP. At the core of our design is the Discrete Wavelet Transform (DWT), used to temporally localise the frequency variations of a signal. Our design exploits transmission mechanisms (including Fast Retransmit/Fast Recovery, Congestion Avoidance, Slow start, and Retransmission Timer Expiry with Exponential Back off.) that are activated in response to changes within this type of network environment. Manipulation of DWT output, combined with the use of novel heuristics permits shifts in the frequency spectrum of composite traffic signals to be directly associated with the former. Our methodology can be adapted to accommodate composite traffic signals that contain a substantial proportion of data originating from non-rate adaptive sources often associated with Long Range Dependence and Self Similarity (e.g. Pareto sources). We demonstrate the methodology in two ways. Firstly, it is used to design a congestion indicator tool that can operate with network control mechanisms that dissipate congestion. Secondly, using a queue management algorithm (Random Early Detection) as a candidate protocol, we show how our methodology can be adapted to produce a performance-monitoring tool. Our approach provides a solution that has both low operational and implementation intrusiveness with respect to existing network infrastructure. The methodology requires a single parameter (i.e. the arrival rate of traffic at a network node), which can be extracted from almost all network-forwarding devices. This simplifies implementation. Our study was performed within the context of fault management with design requirements and constraints arising from an in depth study of the Fault Management Systems (FMS) used by British Telecomm on regional UK networks up to February 2000

Space, the new frontier

Space program - high thrust boosters with greater payload capabilities, superior guidance and control, and astronaut trainin