Optical Space Switches in Data Centers: Issues with Transport Protocols

A number of new architectures for data centre networks employing reconfigurable, SDN controlled, all-optical networks have been reported in recent years. In most cases, additional capacity was added to the system which unsurprisingly improved performance. In this study, a generalised network model that emulates the behaviour of these types of network was developed but where the total capacity is maintained constant so that system behaviour can be understood. An extensive emulated study is presented which indicates that the reconfiguration of such a network can have a detrimental impact on Transmission Control Protocol (TCP) congestion control mechanisms that can degrade the performance of the system. A number of simple scheduling mechanisms were investigated and the results show that an on-demand scheduling mechanism could deliver a throughput increase of more than ∼50% without any increase in total installed network capacity. These results, therefore, indicate the need to link the network resource management with new datacentre network architectures

Topology and congestion invariant in global internet-scale networks

PhDInfrastructures like telecommunication systems, power transmission grids and the Internet are complex networks that are vulnerable to catastrophic failure. A common mechanism behind this kind of failure is avalanche-like breakdown of the network's components. If a component fails due to overload, its load will be redistributed, causing other components to overload and fail. This failure can propagate throughout the entire network. From studies of catastrophic failures in di erent technological networks, the consensus is that the occurrence of a catastrophe is due to the interaction between the connectivity and the dynamical behaviour of the networks' elements. The research in this thesis focuses particularly on packet-oriented networks. In these networks the tra c (dynamics) and the topology (connectivity) are coupled by the routing mechanisms. The interactions between the network's topology and its tra c are complex as they depend on many parameters, e.g. Quality of Service, congestion management (queuing), link bandwidth, link delay, and types of tra c. It is not straightforward to predict whether a network will fail catastrophically or not. Furthermore, even if considering a very simpli ed version of packet networks, there are still fundamental questions about catastrophic behaviour that have not been studied, such as: will a network become unstable and fail catastrophically as its size increases; do catastrophic networks have speci c connectivity properties? One of the main di culties when studying these questions is that, in general, we do not know in advance if a network is going to fail catastrophically. In this thesis we study how to build catastrophic 5 networks. The motivation behind the research is that once we have constructed networks that will fail catastrophically then we can study its behaviour before the catastrophe occurs, for example the dynamical behaviour of the nodes before an imminent catastrophe. Our theoretical and algorithmic approach is based on the observation that for many simple networks there is a topology-tra c invariant for the onset of congestion. We have extended this approach to consider cascading congestion. We have developed two methods to construct catastrophes. The main results in this thesis are that there is a family of catastrophic networks that have a scale invariant; hence at the break point it is possible to predict the behaviour of large networks by studying a much smaller network. The results also suggest that if the tra c on a network increases exponentially, then there is a maximum size that a network can have, after that the network will always fail catastrophically. To verify if catastrophic networks built using our algorithmic approach can re ect real situations, we evaluated the performance of a small catastrophic network. By building the scenario using open source network simulation software OMNet++, we were able to simulate a router network using the Open Shortest Path First routing protocol and carrying User Datagram Protocol tra c. Our results show that this kind of networks can collapse as a cascade of failures. Furthermore, recently the failure of Google Mail routers [1] con rms this kind of catastrophic failure does occur in real situations

Power Systems Monitoring and Control using Telecom Network Management Standards

Historically, different solutions have been developed for power systems control and telecommunications network management environments. The former was characterized by proprietary solutions, while the latter has been involved for years in a strong standardization process guided by criteria of openness. Today, power systems control standardization is in progress, but it is at an early stage compared to the telecommunications management area, especially in terms of information modeling. Today, control equipment tends to exhibit more computational power, and communication lines have increased their performance. These trends hint at some conceptual convergence between power systems and telecommunications networks from a management perspective. This convergence leads us to suggest the application of well-established telecommunications management standards for power systems control. This paper shows that this is a real medium-to-long term possibility

Network emulation focusing on QoS-Oriented satellite communication

This chapter proposes network emulation basics and a complete case study of QoS-oriented Satellite Communication

Towards a sender-based TCP friendly rate control (TFRC) protocol

Pervasive communications are increasingly sent over mobile devices and personal digital assistants. This trend is currently observed by mobile phone service providers which have measured a significant increase in multimedia traffic. To better carry multimedia traffic, the IETF standardized a new TCP Friendly Rate Control (TFRC) protocol. However, the current receiver-based TFRC design is not well suited to resource limited end systems. In this paper, we propose a scheme to shift resource allocation and computation to the sender. This sender-based approach led us to develop a new algorithm for loss notification and loss-rate computation. We detail the complete implementation of a user-level prototype and demonstrate the gain obtained in terms of memory requirements and CPU processing compared to the current design. We also evaluate the performance obtained in terms of throughput smoothness and fairness with TCP and we note this shifting solves security issues raised by classical TFRC implementations

Reasoning About a Service-oriented Programming Paradigm

This paper is about a new way for programming distributed applications: the service-oriented one. It is a concept paper based upon our experience in developing a theory and a language for programming services. Both the theoretical formalization and the language interpreter showed us the evidence that a new programming paradigm exists. In this paper we illustrate the basic features it is characterized by

Analysis domain model for shared virtual environments

The field of shared virtual environments, which also encompasses online games and social 3D environments, has a system landscape consisting of multiple solutions that share great functional overlap. However, there is little system interoperability between the different solutions. A shared virtual environment has an associated problem domain that is highly complex raising difficult challenges to the development process, starting with the architectural design of the underlying system. This paper has two main contributions. The first contribution is a broad domain analysis of shared virtual environments, which enables developers to have a better understanding of the whole rather than the part(s). The second contribution is a reference domain model for discussing and describing solutions - the Analysis Domain Model

Intelligent Integrated Management for Telecommunication Networks

As the size of communication networks keeps on growing, faster connections, cooperating technologies and the divergence of equipment and data communications, the management of the resulting networks gets additional important and time-critical. More advanced tools are needed to support this activity. In this article we describe the design and implementation of a management platform using Artificial Intelligent reasoning technique. For this goal we make use of an expert system. This study focuses on an intelligent framework and a language for formalizing knowledge management descriptions and combining them with existing OSI management model. We propose a new paradigm where the intelligent network management is integrated into the conceptual repository of management information called Managed Information Base (MIB). This paper outlines the development of an expert system prototype based in our propose GDMO+ standard and describes the most important facets, advantages and drawbacks that were found after prototyping our proposal

Modelling & Improving Flow Establishment in RSVP

RSVP has developed as a key component for the evolving Internet, and in particular for the Integrated Services Architecture. Therefore, RSVP performance is crucially important; yet this has been little studied up till now. In this paper, we target one of the most important aspects of RSVP: its ability to establish flows. We first identify the factors influencing the performance of the protocol by modelling the establishment mechanism. Then, we propose a Fast Establishment Mechanism (FEM) aimed at speeding up the set-up procedure in RSVP. We analyse FEM by means of simulation, and show that it offers improvements to the performance of RSVP over a range of likely circumstances