Overlay networks establish logical connections between users on top of the physical network. While randomly connected overlay networks provide only a best effort service, a new generation of structured overlay systems based on Distributed Hash Tables (DHTs) was proposed by the research community. However, there is still a lack of understanding the performance of such DHTs. Additionally, those architectures are highly distributed and therefore appear as a black box to the operator. Yet an operator does not want to lose control over his system and needs to be able to continuously observe and examine its current state at runtime. This work addresses both problems and shows how the solutions can be combined into a more self-organizing overlay concept. At first, we evaluate the performance of structured overlay networks under different aspects and thereby illuminate in how far such architectures are able to support carrier-grade applications. Secondly, to enable operators to monitor and understand their deployed system in more detail, we introduce both active as well as passive methods to gather information about the current state of the overlay network. / Unter einem Overlay Netz versteht man den Zusammenschluss mehrerer Komponenten zu einer logischen Topologie, die auf einer existierenden physikalischen Infrastruktur aufsetzt. Da zufällige Verbindungen zwischen den einzelnen Teilnehmern aber sehr ineffizient sind, wurden strukturierte Overlay Netze entworfen, bei denen die Beziehungen zwischen den einzelnen Teilnehmern fest vorgeschrieben sind. Solche strukturierten Mechanismen versprechen zwar ein großes Potential, dieses wurde aber noch nicht ausreichend untersucht bzw. wissenschaftlich nachgewiesen. In dieser Arbeit wird mit mathematischen Methoden und ereignisorientierter Simulation die Leistungsfähigkeit von strukturierten Overlay Netzen untersucht. Da diese stark von der aktuellen Situation im Overlay abhängt, entwickeln wir Methoden, mit denen sich sowohl passiv, als auch aktiv, wichtige Systemparameter zur Laufzeit abschätzen bzw. messen lassen. Zusammen führen die vorgeschlagenen Methoden zu selbstorganisierenden Mechanismen, die den aktuellen Zustand des Overlays überwachen, diesen bewerten und sich gegebenenfalls automatisch an die aktuellen Verhältnisse anpassen

In future telecommunication systems, we observe an increasing diversity of access networks. The separation of transport services and applications or services leads to multi-network services, i.e., a future service has to work transparently to the underlying network infrastructure. Multi-network services with edge-based intelligence, like P2P file sharing or the Skype VoIP service, impose new traffic control paradigms on the future Internet. Such services adapt the amount of consumed bandwidth to reach different goals. A selfish behavior tries to keep the QoE of a single user above a certain level. Skype, for instance, repeats voice samples depending on the perceived end-to-end loss. From the viewpoint of a single user, the replication of voice data overcomes the degradation caused by packet loss and enables to maintain a certain QoE. The cost for this achievement is a higher amount of consumed bandwidth. However, if the packet loss is caused by congestion in the network, this additionally required bandwidth even worsens the network situation. Altruistic behavior, on the other side, would reduce the bandwidth consumption in such a way that the pressure on the network is released and thus the overall network performance is improved. In this monograph, we analyzed the impact of the overlay, P2P, and QoE paradigms in future Internet applications and the interactions from the observing user behavior. The shift of intelligence toward the edge is accompanied by a change in the emerging user behavior and traffic profile, as well as a change from multi-service networks to multi-networks services. In addition, edge-based intelligence may lead to a higher dynamics in the network topology, since the applications are often controlled by an overlay network, which can rapidly change in size and structure as new nodes can leave or join the overlay network in an entirely distributed manner. As a result, we found that the performance evaluation of such services provides new challenges, since novel key performance factors have to be first identified, like pollution of P2P systems, and appropriate models of the emerging user behavior are required, e.g. taking into account user impatience. As common denominator of the presented studies in this work, we focus on a user-centric view when evaluating the performance of future Internet applications. For a subscriber of a certain application or service, the perceived quality expressed as QoE will be the major criterion of the user's satisfaction with the network and service providers. We selected three different case studies and characterized the application's performance from the end user's point of view. Those are (1) cooperation in mobile P2P file sharing networks, (2) modeling of online TV recording services, and (3) QoE of edge-based VoIP applications. The user-centric approach facilitates the development of new mechanisms to overcome problems arising from the changing user behavior. An example is the proposed CycPriM cooperation strategy, which copes with selfish user behavior in mobile P2P file sharing system. An adequate mechanism has also been shown to be efficient in a heterogeneous B3G network with mobile users conducting vertical handovers between different wireless access technologies. The consideration of the user behavior and the user perceived quality guides to an appropriate modeling of future Internet applications. In the case of the online TV recording service, this enables the comparison between different technical realizations of the system, e.g. using server clusters or P2P technology, to properly dimension the installed network elements and to assess the costs for service providers. Technologies like P2P help to overcome phenomena like flash crowds and improve scalability compared to server clusters, which may get overloaded in such situations. Nevertheless, P2P technology invokes additional challenges and different user behavior to that seen in traditional client/server systems. Beside the willingness to share files and the churn of users, peers may be malicious and offer fake contents to disturb the data dissemination. Finally, the understanding and the quantification of QoE with respect to QoS degradations permits designing sophisticated edge-based applications. To this end, we identified and formulated the IQX hypothesis as an exponential interdependency between QoE and QoS parameters, which we validated for different examples. The appropriate modeling of the emerging user behavior taking into account the user's perceived quality and its interactions with the overlay and P2P paradigm will finally help to design future Internet applications. / Applikationen im heutigen Internet werden immer mehr durch intelligente Endknoten bereitgestellt, deren Kommunikation in logischen, virtuellen Netzwerken, (Overlays) realisiert wird. Die verstärkte Diensterbringung durch solche Overlays, wie zum Beispiel bei Peer-to-Peer Dateitauschbörsen oder Telefonie über das Internet, wird durch einen Paradigmenwechsel von Multi-Service Networks zu Multi-Network Services beschrieben. Während in einem Multi-Service Network verschiedene Dienste innerhalb eines Netzes angeboten werden, beschreibt ein Multi-Network Service die Diensterbringung über verschiedene Netze und Netzzugangstechnologien, wie es im Internet der Fall ist. Dadurch kann die technische Güte des Telekommunikationsdienstes (Quality of Service, QoS) nicht mehr die alleinige Metrik für die Qualität eines Dienstes sein. Stattdessen ist die vom Nutzer erfahrene Dienstgüte (User Perceived Quality of Experience, QoE) zu betrachten. Diese QoE muss entsprechend modelliert werden, um die Performanz von heutigen oder auch zukünftigen Internetapplikationen zu beurteilen. Die Berücksichtigung der QoE beinhaltet unter anderem auch neuartige Verhaltensweisen der Teilnehmer, die ebenfalls modelliert werden müssen. Ein Beispiel ist der Dienstabbruch durch ungeduldige Nutzer beim Herunterladen von Filmen oder bei nicht ausreichender Qualität bei Internet-Telefonie. Durch die Verschiebung der Intelligenz von Applikationen in Richtung Endknoten entstehen neu aufkommende Verhaltensweisen der Teilnehmer und sich ändernde Charakteristika des Netzwerkverkehrs, die sie von klassischen Client-Server-Anwendungen unterscheiden. Beispiele hierfür sind egoistisches oder altruistisches Nutzerverhalten bei der Einbringung von Endnutzer-Ressourcen zur Diensterbringung oder auch bösartiges Nutzerverhalten bei der gezielten Störung eines Dienstes (Pollution). In beiden Fällen sind die zeitdynamischen Verhaltensmuster (Churn, Flash Crowds) zu berücksichtigen. Um die ausgedehnten Overlay. Netze zu planen und zu evaluieren, sind überdies auch neue Leistungsbewertungsmodelle notwendig, damit zum Beispiel die Simulation skaliert oder aber auch zeitdynamische Nutzerverhalten in analytischen Modellen abgebildet wird. Diese Doktorarbeit arbeitet diese Aspekte an drei Anwendungsbeispielen auf: Verteilernetz für Dateiinhalte (Content Distribution Network), Netzwerk-basierte Videorekorder (Online TV Recorder) und Sprachtelefonie über P2P (VoP2P). Die Ergebnisse und Untersuchungen dieser Arbeit gliedern sich entsprechend dieser Anwendungsbeispiele.

Hermes é um arcabouço para a programação de aplicações P2P. Com ele, pode-se criar diversos tipos de aplicações distribuídas, sem se preocupar com a camada de comunicação. O Hermes não é uma implementação de uma rede de sobreposição P2P, e sim uma camada acima das implementações já existentes. O desenvolvedor da aplicação fica isolado da implementação da rede de sobreposição utilizada. Esse isolamento é feito de forma tal que não há limitações quanto à arquitetura de rede utilizada pela implementação, seja ela centralizada, descentralizada, distribuída estruturada ou distribuída não-estruturada. Entre os serviços oferecidos pelo Hermes estão: troca de mensagens, busca, comunicação em grupo e armazenamento distribuído. Geralmente, no início do desenvolvimento de uma aplicação distribuída, tem-se poucas informações sobre o seu tamanho final ou perfil de utilização. O Hermes possibilita ao desenvolvedor da aplicação adiar, até o momento da efetiva implantação do sistema, a decisão sobre qual arquitetura de rede ou qual implementação de rede de sobreposição são as mais apropriadas para suas necessidades. Possibilita também, quando o perfil de utilização muda com o tempo, a troca da implementação utilizada por uma outra que se adeque mais ao novo perfil sem alterações no código da aplicação. / Hermes is a framework for P2P application programming. Using it, one can create several kinds of distributed applications without worrying about the underlying network. Hermes is not a P2P overlay network implementation, but a shell envolving existing implementations. The application developer is isolated from the implementation of the overlay network in use. This isolation is done in a way that poses no limitations on the network architecture used, which may be centralized, decentralized, structured or unstructured. Amongst the services offered by Hermes are: message exchange, search, group communication, and distributed storage. In the early stages of the development of a distributed application, information as to its final size or utilization profile is often unknown. Hermes gives the application developer the possibility of delaying, until the actual moment of system deployment, the decision as to which network architecture or which overlay network implementation is the most appropriate. It also gives the developer the choice, when utilization profile changes over time, of replacing the network implementation with one more suitable to the application needs, without changes on the application code.

The rapid growth of the Internet, in the last few years, has generated a need to enhance the existing IP networks in the areas of availability, dependability and scalability in order to provide a mission critical networking environment. In contemporary IP networks, data packets are routed as a function of the destination address and a single metric such as hop-count or delay. This approach tends to cause message traffic to converge onto the same link, which significantly increases congestion and leads to unbalanced network resource utilization. One solution to this problem is provided by Traffic Engineering (TE), which uses, bandwidth guaranteed, Explicitly Routed Label Switched Paths (ER-LSPs). Due to the dramatic increase in the backbone speeds, current research focuses more on traffic engineering with LSPs for clear control over the traffic distribution in the network. However, the growing popularity of the Internet is driving the Internet Service Providers to adapt new technologies in order to support multiple classes of applications with different characteristics and performance requirements. Multi-Protocol Label Switching (MPLS), which was proposed by the IETF provides essential facilities for traffic engineering and reliable QoS services for the Internet. MPLS networks provide the required flexibility for operators to manage their traffic with ER-LSPs. Even though conventional routing algorithms support the ER-LSP setup in MPLS networks, they are not efficient in link residual capacity information updates and limit resource utilization, which eventually leads to LSP failures and unbalanced network resource utilization. This thesis proposes a new architecture with a cluster based distributed routing algorithm to setup bandwidth guaranteed ER-LSPs in MPLS backbone networks. The proposed routing algorithm confines the route discovery region in order to reduce the routing overhead and computes all possible routes from ingress node to egress node. Based on LSP requirements and network load conditions, the egress node selects the most suitable path from the available paths in order to setup the LSP. This routing scheme optimizes network resource utilization by evenly distributing traffic throughout the network. The Resource Reservation Protocol (RSVP) works in conjunction with the routing protocol for resource reservation and label distribution along the LSP.

The purpose of this study was to ascertain whether simplifying mandibular overdenture treatment utilising single stage surgery and immediate prosthetic loading of a single implant, will achieve similar implant success rates and functional improvement to that expected using conventional techniques. As part of this study, the Mk III Brånemark implant with an oxidised surface (TiUnite™ Nobel Biocare AB, Göteborg, Sweden) was compared to the classical machined Mk III Brånemark fixture.Materials and Methods: 35 patients with a mean age of 68 years and problematic mandibular dentures were treated. The primary complaints among the patients referred to the clinic for treatment related to poor retention of the mandibular denture, instability, denture sores and phonetic problems. Patients were initially placed randomly into the “machined surface” or “oxidised surface” group. A single implant was placed into the mandibular midline with high initial stability. A ball attachment was placed and the retentive cap incorporated into the existing denture. Reviews took place at 3,12 6 6 and 36 months. Clinical assessments, radiographs made with custom film holders, and stability measurements by both manual and resonance frequency analysis methods were recorded. All complications, failures, maintenance and reasons for dropout were noted. Visual analogue scale questionnaires were utilised to record patient satisfaction. (ANOVA p<.05) Results: Three out of 8 machined surface implants failed, representing an unacceptably high failure rate (37.5%). The machined surface was therefore discontinued for this study. Three oxidised surface implants did not achieve sufficient primary stability to be immediately loaded, so were treated with a two stage delayed loading protocol. The 25 immediately loaded oxidised surface implants were all classified as surviving at the 36-month recall. Patient satisfaction was very high with a significant increase in all comfort and functional parameters. Conclusions: Within the limitations of this study and research design, it appears that the immediately loaded single implant retained mandibular overdenture, using an oxidised implant surface in a small group of maladaptive patients, can provide a beneficial treatment outcome over a three year observation period. If insufficient stability at insertion is not achieved for immediate loading, then a delayed loading protocol should be utilised.

Tungsten carbide-based metal matrix composite coatings are deposited by PTAW (Plasma Transferred Arc Welding) on production critical components in oil sands mining. Homogeneous distribution of the reinforcement particles is desirable for optimal wear resistance in order to reduce unplanned maintenance shutdowns. The homogeneity of the coating can be improved by controlling the heat transfer, solidification rate of the process and the volume fraction of carbide. The degree of settling of the particles in the deposit was quantified using image analysis. The volume fraction of carbide was the most significant factor in obtaining a homogeneous coating. Lowering the current made a modest improvement in homogeneity. Changes made in other operational parameters did not effect significant changes in homogeneity. Infrared thermography was used to measure the temperature of the surface of the deposit during the welding process. The emissivity of the materials was required to acquire true temperature readings. The emissivity of the deposit was measured using laser reflectometry and was found to decrease from 0.8 to 0.2 as the temperature increased from 900C to 1200C. A correction algorithm was applied to calculate the actual temperature of the surface of the deposit. The corrected temperature did increase as the heat input of the weld increased. A one dimensional mathematical model of the settling profile and solidification of the coatings was developed. The model considers convective and radiative heat input from the plasma, the build-up of the deposit, solidification of the deposit and the settling of the WC particles within the deposit. The model had very good agreement with the experimental results of the homogeneity of the carbide as a function of depth. This fundamental model was able to accurately predict the particle homogeneity of an MMC deposited by an extremely complicated process. It was shown that the most important variable leading to a homogeneous coating is to operate at the packing saturation limit of the reinforcement. In the case of the MMC explored, a fully homogeneous coating was obtained with 50 vol% WC in a NiCrBSi matrix. / Materials Engineering

This dissertation presents algorithms for data structures called distributed hash tables (DHT) or structured overlay networks, which are used to build scalable self-managing distributed systems. The provided algorithms guarantee lookup consistency in the presence of dynamism: they guarantee consistent lookup results in the presence of nodes joining and leaving. Similarly, the algorithms guarantee that routing never fails while nodes join and leave. Previous algorithms for lookup consistency either suffer from starvation, do not work in the presence of failures, or lack proof of correctness. Several group communication algorithms for structured overlay networks are presented. We provide an overlay broadcast algorithm, which unlike previous algorithms avoids redundant messages, reaching all nodes in O(log n) time, while using O(n) messages, where n is the number of nodes in the system. The broadcast algorithm is used to build overlay multicast. We introduce bulk operation, which enables a node to efficiently make multiple lookups or send a message to all nodes in a specified set of identifiers. The algorithm ensures that all specified nodes are reached in O(log n) time, sending maximum O(log n) messages per node, regardless of the input size of the bulk operation. Moreover, the algorithm avoids sending redundant messages. Previous approaches required multiple lookups, which consume more messages and can render the initiator a bottleneck. Our algorithms are used in DHT-based storage systems, where nodes can do thousands of lookups to fetch large files. We use the bulk operation algorithm to construct a pseudo-reliable broadcast algorithm. Bulk operations can also be used to implement efficient range queries. Finally, we describe a novel way to place replicas in a DHT, called symmetric replication, that enables parallel recursive lookups. Parallel lookups are known to reduce latencies. However, costly iterative lookups have previously been used to do parallel lookups. Moreover, joins or leaves only require exchanging O(1) messages, while other schemes require at least log(f) messages for a replication degree of f. The algorithms have been implemented in a middleware called the Distributed k-ary System (DKS), which is briefly described. / QC 20100824

Self-organizing overlay networks have emerged as a powerful paradigm for providing network services. While most approaches assume that overlay networks are built over a single substrate network, generally, the Internet, this thesis addresses the construction of overlay networks over multiple substrate networks. We present the design, implementation and evaluation of Cross-Substrate Advertisement (CSA) mechanisms for overlay networks over multiple heterogeneous substrate networks. A key difficulty arises from the more complex address bindings, since a single logical identifier is bound to multiple substrate addresses. We present mechanisms for exchanging information on address bindings and evaluate their effectiveness. The CSA mechanisms have been implemented in the HyperCast overlay protocol architecture, and have been evaluated in measurement experiments on an Emulab testbed. The experiments show that our CSA methods are effective in disseminating address information in large networks and are robust in the presence of network disruptions.

Self-organizing overlay networks have emerged as a powerful paradigm for providing network services. While most approaches assume that overlay networks are built over a single substrate network, generally, the Internet, this thesis addresses the construction of overlay networks over multiple substrate networks. We present the design, implementation and evaluation of Cross-Substrate Advertisement (CSA) mechanisms for overlay networks over multiple heterogeneous substrate networks. A key difficulty arises from the more complex address bindings, since a single logical identifier is bound to multiple substrate addresses. We present mechanisms for exchanging information on address bindings and evaluate their effectiveness. The CSA mechanisms have been implemented in the HyperCast overlay protocol architecture, and have been evaluated in measurement experiments on an Emulab testbed. The experiments show that our CSA methods are effective in disseminating address information in large networks and are robust in the presence of network disruptions.

Middleware has become a key enabler for the development of distributed applications. Unfortunately, conventional middleware technologies do not yet offer sufficient functionality to make them suitable for mobile environments. This dissertation proposes a novel middleware approach termed opportunistic overlays and its dynamically reconfigurable support framework for building efficient mobile applications. Specifically, we address the inefficiency of content delivery introduced by node mobility and by dynamically changing system loads, in the context of publish/subscribe systems. In response to changes in physical network topology, in nodes' physical locations, and in network node behaviors, the opportunistic overlay approach dynamically adapts event dissemination structures (i.e., broker overlays) with the goal of optimizing end-to-end delays in event delivery. Adaptation techniques include the dynamic construction of broker overlay networks, runtime changes of mobile clients' assignments to brokers, and dynamic broker load balancing. Essentially, opportunistic overlays implement a middleware-level analogue of the networking routing protocols used in wireless communications (i.e., Mobile IP, AODV, DSR and DSDV). By thus coordinating network- with middleware-level routing, opportunistic overlays can attain substantial performance improvements over non-adaptive event systems. Such improvements are due to their use of shorter network paths and better balancing of loads across event brokers. Opportunistic overlays and the adaptive methods they use are realized by a set of distributed protocols implemented in a Java-based publish/subscribe infrastructure. Comprehensive performance evaluations are performed via simulation, emulation, and with two representative applications on actual networks. Experimental results demonstrate that the opportunistic overlay approach is practically applicable and that the performance advantages attained from the use of opportunistic overlays can be substantial, in both infrastructure-based mobile environments and mobile ad hoc networks.