O advento dos computadores pessoais e posteriormente das estações de trabalho, somado ao desenvolvimento de hardware de comunicação eficiente e de baixo custo, levou a popularização das redes locais. Entretanto, o software não presenciou o mesmo desenvolvimento do hardware, especialmente devido a complexidade dos sistemas distribuídos. A heterogeneidade das máquinas, sistemas e redes, inerente aos ambientes computacionais modernos, restringe igualmente a integração e cooperação entre os nodos disponíveis. 0 objetivo do presente trabalho é, a partir da análise dos principais aspectos relacionados à distribuição e à heterogeneidade, desenvolver um sistema operacional de rede heterogêneo. Tal sistema, denominado HetNOS (de Heterogeneous Network Operating System), permite o desenvolvimento e validação de aplicações distribuídas homogêneas e heterogêneas de forma rápida e fácil. Os usuários podem concentrar-se nos aspectos de distribuição dos algoritmos, abstraindo detalhes dos mecanismos de comunicação, pois a programação de aplicações distribuídas é baseada em uma plataforma de interface homogênea, fácil de usar e com independência de localidade. Sendo um sistema operacional de rede, o HetNOS atua sobre o conjunto de sistemas operacionais nativos existentes; o ambiente de trabalho e estendido e não substituído. Não há entidades nem informações centralizadas, e os algoritmos são distribuídos, usualmente resultando maior confiabilidade e desempenho. A topologia do sistema é um anel lógico, esquema justificado pela generalidade de tal configuração e pela simplificação do projeto do núcleo distribuído do HetNOS. O paradigma de comunicação entre módulos e a troca de mensagens, mecanismo implementado sobre a interface de programação em rede sockets. Não há compartilhamento de memória em nenhuma instância, tornando o sistema mais legível, manutenível e portável. A interpelação entre módulos fica restrita à interface de mensagens definidas e aceitas por cada módulo. A arquitetura do HetNOS é estruturada e distribuída, pois o sistema é composto de camadas hierárquicas subdivididas em módulos, estes implementados com processos. O nível 1 corresponde ao conjunto de núcleos de sistemas operacionais nativos suportados, sobre o qual é implementado o núcleo distribuído heterogêneo do HetNOS, a DCL (Distributed Computing Layer). O principal serviço fornecido pela DCL (executada no nível 2), é um subsistema de troca de mensagens canônico e independente de localidade. Processos servidores e de usuários podem utilizar as mais variadas formas de comunicação por mensagens, tal como envio, recepção e propagação de mensagens síncronas, assíncronas, bloqueantes e não bloqueantes. No nível 3 estão os servidores do sistema, que estendem e implementam de forma distribuída a funcionalidade do sistema nativo. O Servidor de Nomes é o repositório global de dados, servindo a processos do sistema e de usuários. O Servidor de Autorização implementa o esquema de controle no acesso a recursos do sistema. O Servidor de Tipos permite que aplicações copiem dados estruturados de forma independente de localidade e de arquitetura. Por fim, o Servidor de Arquivos estende os serviços (de arquivos) locais de forma a integrá-los em um único domínio (espaço). No nível 4, arquiteturas e sistemas operacionais são emulados por módulos interpretadores (denominados Emulators). Aplicações de usuários estão espalhadas dos níveis 2 a 5; a camada varia com o tipo de aplicação. Para demonstrar a viabilidade do sistema, implementou-se a estrutura fundamental do HetNOS, incluindo a DCL (um núcleo distribuído heterogêneo), a versões básicas dos módulos servidores, as bibliotecas de procedimentos, além de diversos tipos de aplicações. O sistema conta hoje com mais de 25.000 linhas de código fonte C em mais de 100 arquivos. O desempenho do subsistema de comunicação implementado pela DCL (em avaliações com diferentes configurações de hardware) superou as expectativas iniciais, mas ainda está muito aquém do necessário a aplicações distribuídas. Segundo o que indicam as primeiras experiências realizadas, o HetNOS será bastante útil na prototipação e avaliação de modelos distribuídos, assim como na programação de software distribuído homogêneo e heterogêneo. Projetos de pesquisa do CPGCC envolvendo sistemas distribuídos (p.ex., tolerância a falhas e simulações) podem utilizar o HetNOS como ferramenta para implementação e validação de seus modelos. Futuramente, aplicações distribuídas e paralelas de maior porte poderão ser programadas, como sistemas de gerencia de bases de dados distribuídas, simuladores e sistemas de controle para automação industrial. / The advent of personal computers and, later, of workstations, along with the development of efficient and low-cost communication hardware has led to the popularization of local-area networks. However, distributed software did not experiment the same development of hardware, specially due to the complexity of distributed systems. The machine, system and communication network heterogeneity, inherent to the modern computing environments, is also responsible for the lack of integration and cooperation of available nodes. The purpose of this work is, from the analysis of the main aspects related to distribution and heterogeneity, to design a heterogeneous network operating system. Such system, named HetNOS (which stands for Heterogeneous Network Operating System), allows users to quickly write and validate distributed homogeneous and heterogeneous applications. Users can concentrate their work in the distributed aspects, abstracting communication mechanisms' details, because programming of distributed applications is based on a homogeneous interface platform, easy to use and location-independent. Being a network operating system, HetNOS acts over the set of native operating systems; the environment is extended instead of substituted. There are neither centralized information nor entities, and the algorithms are always distributed, usually yielding more reliability and performance. The HetNOS topology is a logical ring, scheme adopted partly due to the generality of such configuration and partly to simplify the HetNOS distributed kernel design. The communication paradigm between modules is the message exchange, a mechanism implemented over the sockets network application programming interface. There is no shared memory at all, making the system clearer, more manutible and portable. The interrelation between modules is restricted to the message interface defined and accepted by a module. The HetNOS architecture is structured and distributed, as the system is composed of hierarchical layers divided into modules, which in their turn are realized as processes. The layer 1 is the set of native operating system kernels, over which is implemented the distributed heterogeneous HetNOS kernel, namely DCL (states for Distributed Computing Layer). The main service provided by DCL (in layer 2) is a canonical, location-independent, message exchange mechanism. Server and user processes may use multiple forms of message primitives, such as synchronous, asynchronous, blocking and non-blocking send and receive. In the layer 3 are the system servers, which extend and implement in a distributed way the functionality of native systems. The name server is a global data repository, serving other system and user processes. The authorization server implements the security scheme to control the access to the system resources. The type server allows applications to transfer structured data independently of location and architecture. Finally, the file server extends the local (file) services to integrate them into a unique domain (space). In the layer 4, architectures and operating systems are emulated by interpreter modules (named Emulators). User applications are spread over the layers 2 to 5, depending on the application type. In order to prove the system viability, the fundamental HetNOS structure has been implemented, including its distributed heterogeneous kernel, the base of server modules, the procedure libraries, and several types of applications. The system source code has over 25,000 lines of C programming distributed over a hundred files. Although the optimization is an endless process, the performance of the DCL communication subsystem (evaluated using a few different hardware configurations) overestimated initial predictions, but is weak if considered the requirements to distributed processing. Accordingly to the first experiences made, HetNOS will be of great value to evaluate and prototype distributed models, as well as to the programming of homogeneous and heterogeneous distributed software. Local research projects involving distributed systems (e.g., fault tolerance and simulations) may use HetNOS as a tool to validate and implement their models. In the future, more complex distributed and parallel applications will be programmed, such as a distributed database management system, simulators and factory automation control systems.

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

Numerous cryptographic applications require a trusted authority to hold a secret. With a plethora of malicious attacks over the Internet, however, it is difficult to establish and maintain such an authority in online systems. Secret-sharing schemes attempt to solve this problem by distributing the required trust to hold and use the secret over multiple servers; however, they still require a trusted {\em dealer} to choose and share the secret, and have problems related to single points of failure and key escrow. A distributed key generation (DKG) scheme overcomes these hurdles by removing the requirement of a dealer in secret sharing. A (threshold) DKG scheme achieves this using a complete distribution of the trust among a number of servers such that any subset of servers of size greater than a given threshold can reveal or use the shared secret, while any smaller subset cannot. In this thesis, we make contributions to DKG in the computational security setting and describe three applications of it. We first define a constant-size commitment scheme for univariate polynomials over finite fields and use it to reduce the size of broadcasts required for DKG protocols in the synchronous communication model by a linear factor. Further, we observe that the existing (synchronous) DKG protocols do not provide a liveness guarantee over the Internet and design the first DKG protocol for use over the Internet. Observing the necessity of long-term stability, we then present proactive security and group modification protocols for our DKG system. We also demonstrate the practicality of our DKG protocol over the Internet by testing our implementation over PlanetLab. For the applications, we use our DKG protocol to define IND-ID-CCA secure distributed private-key generators (PKGs) for three important identity-based encryption (IBE) schemes: Boneh and Franklin's BF-IBE, Sakai and Kasahara's SK-IBE, and Boneh and Boyen's BB1-IBE. These IBE schemes cover all three important IBE frameworks: full-domain-hash IBEs, exponent-inversion IBEs and commutative-blinding IBEs respectively, and our distributed PKG constructions can easily be modified for other IBE schemes in these frameworks. As the second application, we use our distributed PKG for BF-IBE to define an onion routing circuit construction mechanism in the identity-based setting, which solves the scalability problem in single-pass onion routing circuit construction without hampering forward secrecy. As the final application, we use our DKG implementation to design a threshold signature architecture for quorum-based distributed hash tables and use it to define two robust communication protocols in these peer-to-peer systems.

Numerous cryptographic applications require a trusted authority to hold a secret. With a plethora of malicious attacks over the Internet, however, it is difficult to establish and maintain such an authority in online systems. Secret-sharing schemes attempt to solve this problem by distributing the required trust to hold and use the secret over multiple servers; however, they still require a trusted {\em dealer} to choose and share the secret, and have problems related to single points of failure and key escrow. A distributed key generation (DKG) scheme overcomes these hurdles by removing the requirement of a dealer in secret sharing. A (threshold) DKG scheme achieves this using a complete distribution of the trust among a number of servers such that any subset of servers of size greater than a given threshold can reveal or use the shared secret, while any smaller subset cannot. In this thesis, we make contributions to DKG in the computational security setting and describe three applications of it. We first define a constant-size commitment scheme for univariate polynomials over finite fields and use it to reduce the size of broadcasts required for DKG protocols in the synchronous communication model by a linear factor. Further, we observe that the existing (synchronous) DKG protocols do not provide a liveness guarantee over the Internet and design the first DKG protocol for use over the Internet. Observing the necessity of long-term stability, we then present proactive security and group modification protocols for our DKG system. We also demonstrate the practicality of our DKG protocol over the Internet by testing our implementation over PlanetLab. For the applications, we use our DKG protocol to define IND-ID-CCA secure distributed private-key generators (PKGs) for three important identity-based encryption (IBE) schemes: Boneh and Franklin's BF-IBE, Sakai and Kasahara's SK-IBE, and Boneh and Boyen's BB1-IBE. These IBE schemes cover all three important IBE frameworks: full-domain-hash IBEs, exponent-inversion IBEs and commutative-blinding IBEs respectively, and our distributed PKG constructions can easily be modified for other IBE schemes in these frameworks. As the second application, we use our distributed PKG for BF-IBE to define an onion routing circuit construction mechanism in the identity-based setting, which solves the scalability problem in single-pass onion routing circuit construction without hampering forward secrecy. As the final application, we use our DKG implementation to design a threshold signature architecture for quorum-based distributed hash tables and use it to define two robust communication protocols in these peer-to-peer systems.

O advento dos computadores pessoais e posteriormente das estações de trabalho, somado ao desenvolvimento de hardware de comunicação eficiente e de baixo custo, levou a popularização das redes locais. Entretanto, o software não presenciou o mesmo desenvolvimento do hardware, especialmente devido a complexidade dos sistemas distribuídos. A heterogeneidade das máquinas, sistemas e redes, inerente aos ambientes computacionais modernos, restringe igualmente a integração e cooperação entre os nodos disponíveis. 0 objetivo do presente trabalho é, a partir da análise dos principais aspectos relacionados à distribuição e à heterogeneidade, desenvolver um sistema operacional de rede heterogêneo. Tal sistema, denominado HetNOS (de Heterogeneous Network Operating System), permite o desenvolvimento e validação de aplicações distribuídas homogêneas e heterogêneas de forma rápida e fácil. Os usuários podem concentrar-se nos aspectos de distribuição dos algoritmos, abstraindo detalhes dos mecanismos de comunicação, pois a programação de aplicações distribuídas é baseada em uma plataforma de interface homogênea, fácil de usar e com independência de localidade. Sendo um sistema operacional de rede, o HetNOS atua sobre o conjunto de sistemas operacionais nativos existentes; o ambiente de trabalho e estendido e não substituído. Não há entidades nem informações centralizadas, e os algoritmos são distribuídos, usualmente resultando maior confiabilidade e desempenho. A topologia do sistema é um anel lógico, esquema justificado pela generalidade de tal configuração e pela simplificação do projeto do núcleo distribuído do HetNOS. O paradigma de comunicação entre módulos e a troca de mensagens, mecanismo implementado sobre a interface de programação em rede sockets. Não há compartilhamento de memória em nenhuma instância, tornando o sistema mais legível, manutenível e portável. A interpelação entre módulos fica restrita à interface de mensagens definidas e aceitas por cada módulo. A arquitetura do HetNOS é estruturada e distribuída, pois o sistema é composto de camadas hierárquicas subdivididas em módulos, estes implementados com processos. O nível 1 corresponde ao conjunto de núcleos de sistemas operacionais nativos suportados, sobre o qual é implementado o núcleo distribuído heterogêneo do HetNOS, a DCL (Distributed Computing Layer). O principal serviço fornecido pela DCL (executada no nível 2), é um subsistema de troca de mensagens canônico e independente de localidade. Processos servidores e de usuários podem utilizar as mais variadas formas de comunicação por mensagens, tal como envio, recepção e propagação de mensagens síncronas, assíncronas, bloqueantes e não bloqueantes. No nível 3 estão os servidores do sistema, que estendem e implementam de forma distribuída a funcionalidade do sistema nativo. O Servidor de Nomes é o repositório global de dados, servindo a processos do sistema e de usuários. O Servidor de Autorização implementa o esquema de controle no acesso a recursos do sistema. O Servidor de Tipos permite que aplicações copiem dados estruturados de forma independente de localidade e de arquitetura. Por fim, o Servidor de Arquivos estende os serviços (de arquivos) locais de forma a integrá-los em um único domínio (espaço). No nível 4, arquiteturas e sistemas operacionais são emulados por módulos interpretadores (denominados Emulators). Aplicações de usuários estão espalhadas dos níveis 2 a 5; a camada varia com o tipo de aplicação. Para demonstrar a viabilidade do sistema, implementou-se a estrutura fundamental do HetNOS, incluindo a DCL (um núcleo distribuído heterogêneo), a versões básicas dos módulos servidores, as bibliotecas de procedimentos, além de diversos tipos de aplicações. O sistema conta hoje com mais de 25.000 linhas de código fonte C em mais de 100 arquivos. O desempenho do subsistema de comunicação implementado pela DCL (em avaliações com diferentes configurações de hardware) superou as expectativas iniciais, mas ainda está muito aquém do necessário a aplicações distribuídas. Segundo o que indicam as primeiras experiências realizadas, o HetNOS será bastante útil na prototipação e avaliação de modelos distribuídos, assim como na programação de software distribuído homogêneo e heterogêneo. Projetos de pesquisa do CPGCC envolvendo sistemas distribuídos (p.ex., tolerância a falhas e simulações) podem utilizar o HetNOS como ferramenta para implementação e validação de seus modelos. Futuramente, aplicações distribuídas e paralelas de maior porte poderão ser programadas, como sistemas de gerencia de bases de dados distribuídas, simuladores e sistemas de controle para automação industrial. / The advent of personal computers and, later, of workstations, along with the development of efficient and low-cost communication hardware has led to the popularization of local-area networks. However, distributed software did not experiment the same development of hardware, specially due to the complexity of distributed systems. The machine, system and communication network heterogeneity, inherent to the modern computing environments, is also responsible for the lack of integration and cooperation of available nodes. The purpose of this work is, from the analysis of the main aspects related to distribution and heterogeneity, to design a heterogeneous network operating system. Such system, named HetNOS (which stands for Heterogeneous Network Operating System), allows users to quickly write and validate distributed homogeneous and heterogeneous applications. Users can concentrate their work in the distributed aspects, abstracting communication mechanisms' details, because programming of distributed applications is based on a homogeneous interface platform, easy to use and location-independent. Being a network operating system, HetNOS acts over the set of native operating systems; the environment is extended instead of substituted. There are neither centralized information nor entities, and the algorithms are always distributed, usually yielding more reliability and performance. The HetNOS topology is a logical ring, scheme adopted partly due to the generality of such configuration and partly to simplify the HetNOS distributed kernel design. The communication paradigm between modules is the message exchange, a mechanism implemented over the sockets network application programming interface. There is no shared memory at all, making the system clearer, more manutible and portable. The interrelation between modules is restricted to the message interface defined and accepted by a module. The HetNOS architecture is structured and distributed, as the system is composed of hierarchical layers divided into modules, which in their turn are realized as processes. The layer 1 is the set of native operating system kernels, over which is implemented the distributed heterogeneous HetNOS kernel, namely DCL (states for Distributed Computing Layer). The main service provided by DCL (in layer 2) is a canonical, location-independent, message exchange mechanism. Server and user processes may use multiple forms of message primitives, such as synchronous, asynchronous, blocking and non-blocking send and receive. In the layer 3 are the system servers, which extend and implement in a distributed way the functionality of native systems. The name server is a global data repository, serving other system and user processes. The authorization server implements the security scheme to control the access to the system resources. The type server allows applications to transfer structured data independently of location and architecture. Finally, the file server extends the local (file) services to integrate them into a unique domain (space). In the layer 4, architectures and operating systems are emulated by interpreter modules (named Emulators). User applications are spread over the layers 2 to 5, depending on the application type. In order to prove the system viability, the fundamental HetNOS structure has been implemented, including its distributed heterogeneous kernel, the base of server modules, the procedure libraries, and several types of applications. The system source code has over 25,000 lines of C programming distributed over a hundred files. Although the optimization is an endless process, the performance of the DCL communication subsystem (evaluated using a few different hardware configurations) overestimated initial predictions, but is weak if considered the requirements to distributed processing. Accordingly to the first experiences made, HetNOS will be of great value to evaluate and prototype distributed models, as well as to the programming of homogeneous and heterogeneous distributed software. Local research projects involving distributed systems (e.g., fault tolerance and simulations) may use HetNOS as a tool to validate and implement their models. In the future, more complex distributed and parallel applications will be programmed, such as a distributed database management system, simulators and factory automation control systems.

O advento dos computadores pessoais e posteriormente das estações de trabalho, somado ao desenvolvimento de hardware de comunicação eficiente e de baixo custo, levou a popularização das redes locais. Entretanto, o software não presenciou o mesmo desenvolvimento do hardware, especialmente devido a complexidade dos sistemas distribuídos. A heterogeneidade das máquinas, sistemas e redes, inerente aos ambientes computacionais modernos, restringe igualmente a integração e cooperação entre os nodos disponíveis. 0 objetivo do presente trabalho é, a partir da análise dos principais aspectos relacionados à distribuição e à heterogeneidade, desenvolver um sistema operacional de rede heterogêneo. Tal sistema, denominado HetNOS (de Heterogeneous Network Operating System), permite o desenvolvimento e validação de aplicações distribuídas homogêneas e heterogêneas de forma rápida e fácil. Os usuários podem concentrar-se nos aspectos de distribuição dos algoritmos, abstraindo detalhes dos mecanismos de comunicação, pois a programação de aplicações distribuídas é baseada em uma plataforma de interface homogênea, fácil de usar e com independência de localidade. Sendo um sistema operacional de rede, o HetNOS atua sobre o conjunto de sistemas operacionais nativos existentes; o ambiente de trabalho e estendido e não substituído. Não há entidades nem informações centralizadas, e os algoritmos são distribuídos, usualmente resultando maior confiabilidade e desempenho. A topologia do sistema é um anel lógico, esquema justificado pela generalidade de tal configuração e pela simplificação do projeto do núcleo distribuído do HetNOS. O paradigma de comunicação entre módulos e a troca de mensagens, mecanismo implementado sobre a interface de programação em rede sockets. Não há compartilhamento de memória em nenhuma instância, tornando o sistema mais legível, manutenível e portável. A interpelação entre módulos fica restrita à interface de mensagens definidas e aceitas por cada módulo. A arquitetura do HetNOS é estruturada e distribuída, pois o sistema é composto de camadas hierárquicas subdivididas em módulos, estes implementados com processos. O nível 1 corresponde ao conjunto de núcleos de sistemas operacionais nativos suportados, sobre o qual é implementado o núcleo distribuído heterogêneo do HetNOS, a DCL (Distributed Computing Layer). O principal serviço fornecido pela DCL (executada no nível 2), é um subsistema de troca de mensagens canônico e independente de localidade. Processos servidores e de usuários podem utilizar as mais variadas formas de comunicação por mensagens, tal como envio, recepção e propagação de mensagens síncronas, assíncronas, bloqueantes e não bloqueantes. No nível 3 estão os servidores do sistema, que estendem e implementam de forma distribuída a funcionalidade do sistema nativo. O Servidor de Nomes é o repositório global de dados, servindo a processos do sistema e de usuários. O Servidor de Autorização implementa o esquema de controle no acesso a recursos do sistema. O Servidor de Tipos permite que aplicações copiem dados estruturados de forma independente de localidade e de arquitetura. Por fim, o Servidor de Arquivos estende os serviços (de arquivos) locais de forma a integrá-los em um único domínio (espaço). No nível 4, arquiteturas e sistemas operacionais são emulados por módulos interpretadores (denominados Emulators). Aplicações de usuários estão espalhadas dos níveis 2 a 5; a camada varia com o tipo de aplicação. Para demonstrar a viabilidade do sistema, implementou-se a estrutura fundamental do HetNOS, incluindo a DCL (um núcleo distribuído heterogêneo), a versões básicas dos módulos servidores, as bibliotecas de procedimentos, além de diversos tipos de aplicações. O sistema conta hoje com mais de 25.000 linhas de código fonte C em mais de 100 arquivos. O desempenho do subsistema de comunicação implementado pela DCL (em avaliações com diferentes configurações de hardware) superou as expectativas iniciais, mas ainda está muito aquém do necessário a aplicações distribuídas. Segundo o que indicam as primeiras experiências realizadas, o HetNOS será bastante útil na prototipação e avaliação de modelos distribuídos, assim como na programação de software distribuído homogêneo e heterogêneo. Projetos de pesquisa do CPGCC envolvendo sistemas distribuídos (p.ex., tolerância a falhas e simulações) podem utilizar o HetNOS como ferramenta para implementação e validação de seus modelos. Futuramente, aplicações distribuídas e paralelas de maior porte poderão ser programadas, como sistemas de gerencia de bases de dados distribuídas, simuladores e sistemas de controle para automação industrial. / The advent of personal computers and, later, of workstations, along with the development of efficient and low-cost communication hardware has led to the popularization of local-area networks. However, distributed software did not experiment the same development of hardware, specially due to the complexity of distributed systems. The machine, system and communication network heterogeneity, inherent to the modern computing environments, is also responsible for the lack of integration and cooperation of available nodes. The purpose of this work is, from the analysis of the main aspects related to distribution and heterogeneity, to design a heterogeneous network operating system. Such system, named HetNOS (which stands for Heterogeneous Network Operating System), allows users to quickly write and validate distributed homogeneous and heterogeneous applications. Users can concentrate their work in the distributed aspects, abstracting communication mechanisms' details, because programming of distributed applications is based on a homogeneous interface platform, easy to use and location-independent. Being a network operating system, HetNOS acts over the set of native operating systems; the environment is extended instead of substituted. There are neither centralized information nor entities, and the algorithms are always distributed, usually yielding more reliability and performance. The HetNOS topology is a logical ring, scheme adopted partly due to the generality of such configuration and partly to simplify the HetNOS distributed kernel design. The communication paradigm between modules is the message exchange, a mechanism implemented over the sockets network application programming interface. There is no shared memory at all, making the system clearer, more manutible and portable. The interrelation between modules is restricted to the message interface defined and accepted by a module. The HetNOS architecture is structured and distributed, as the system is composed of hierarchical layers divided into modules, which in their turn are realized as processes. The layer 1 is the set of native operating system kernels, over which is implemented the distributed heterogeneous HetNOS kernel, namely DCL (states for Distributed Computing Layer). The main service provided by DCL (in layer 2) is a canonical, location-independent, message exchange mechanism. Server and user processes may use multiple forms of message primitives, such as synchronous, asynchronous, blocking and non-blocking send and receive. In the layer 3 are the system servers, which extend and implement in a distributed way the functionality of native systems. The name server is a global data repository, serving other system and user processes. The authorization server implements the security scheme to control the access to the system resources. The type server allows applications to transfer structured data independently of location and architecture. Finally, the file server extends the local (file) services to integrate them into a unique domain (space). In the layer 4, architectures and operating systems are emulated by interpreter modules (named Emulators). User applications are spread over the layers 2 to 5, depending on the application type. In order to prove the system viability, the fundamental HetNOS structure has been implemented, including its distributed heterogeneous kernel, the base of server modules, the procedure libraries, and several types of applications. The system source code has over 25,000 lines of C programming distributed over a hundred files. Although the optimization is an endless process, the performance of the DCL communication subsystem (evaluated using a few different hardware configurations) overestimated initial predictions, but is weak if considered the requirements to distributed processing. Accordingly to the first experiences made, HetNOS will be of great value to evaluate and prototype distributed models, as well as to the programming of homogeneous and heterogeneous distributed software. Local research projects involving distributed systems (e.g., fault tolerance and simulations) may use HetNOS as a tool to validate and implement their models. In the future, more complex distributed and parallel applications will be programmed, such as a distributed database management system, simulators and factory automation control systems.

<div>Dynamic Binary Instrumentation (DBI) is one way to monitor a distributed system in real-time without modifying source code. Previous work has shown it is possible to instrument distributed systems using standards-based distributed middleware. Existing work, however, only applies to a single middleware, such as CORBA.</div><div><br></div><div>This thesis therefore presents a tool named the Standards-based Distributed Middleware Monitor (SDMM), which generalizes two modern standards-based distributed middleware, the Data Distribution Service (DDS) and gRemote Procedure Call (gRPC). SDMM uses DBI to extract values and other data relevant to monitoring a distributed system in real-time. Using dynamic instrumentation allows SDMM to capture information without a priori knowledge of the distributed system under instrumentation. We applied SDMM to systems created with two DDS vendors, RTI Connext DDS and OpenDDS, as well as gRPC which is a complete remote procedure call framework. Our results show that the data collection process contributes to less than 2% of the run-time overhead in all test cases.</div>

Most common object models of distributed object systems have a limited set of object-oriented features, lacking the advanced features of `polymorphism' (an abstraction mechanism that represents a quality or state of being able to assume different forms) and `concurrency' (the ability to have more than one thread of execution in an object simultaneously). The lack of support for advanced features is a serious limitation because it restricts the development of new components and limits reuse of existing of components that use these advanced features. As a result, wrappers must be used that hide the advanced features or components must be re-implemented using only the features of the common object model. In this dissertation, a new direction of research centered on a subset of object-oriented languages, specifically statically typed languages, is considered. One of the major drawbacks of existing distributed object systems is that they cater to a broad domain of programming languages including both object-oriented as well as non object-oriented languages. Mapping an object model into a non object-oriented language is a complex task and it does not appear natural to a native language user. The interoperable common object model (ICOM) proposed in this dissertation is an attempt to elevate common object models (with the advanced features of polymorphism and concurrency) closer to the object models of statically typed object-oriented languages. Specific features of the ICOM object model include: remote inheritance, method overloading, parameterized types, and guard methods. The actor model and reflection techniques are used to develop a uniform implementation framework for the ICOM object model in C++ and Modula-3. Prototype applications were implemented to demonstrate the utility of the advanced features of the ICOM object model. The main contributions of this dissertation are: design and implementation of a powerful common object model, an architecture for distributed compilation, and an implementation of a distributed object model using the actor model. / Ph. D.

In this dissertation, we develop feedback control strategies that can be used for evacuating people. Pedestrian models are based on macroscopic or microscopic behavior. We use the macroscopic modeling approach, where pedestrians are treated in an aggregate way and detailed interactions are overlooked. The models representing evacuation dynamics are based on the laws of conservation of mass and momentum and are described by nonlinear hyperbolic partial differential equations. As such the system is distributed in nature. We address the design of feedback control for these models in a distributed setting where the problem of control and stability is formulated directly in the framework of partial differential equations. The control goal is to design feedback controllers to control the movement of people during evacuation and avoid jams and shocks. We design the feedback controllers for both diffusion and advection where the density of people diffuses as well as moves in a specified direction with time. In order to achieve this goal we are assuming that the control variables have no bounds. However, it is practically impossible to have unbounded controls so we modify the controllers in order to take the effect of control saturation into account. We also discuss the feedback control for these models in presence of uncertainties where the goal is to design controllers to minimize the effect of uncertainties on the movement of people during evacuation. The control design technique adopted in all these cases is feedback linearization which includes backstepping for higher order two-equation models, Lyapunov redesign for uncertain models and robust backstepping for two-equation uncertain models. The work also focuses on abstraction of evacuation system which focuses on obtaining models with lesser number of partial differential equations than the original one. The feedback control design of a higher level two-equation model is more difficult than the lower order one-equation model. Therefore, it is desirable to perform control design for a simpler abstracted model and then transform control design back to the original model. / Ph. D.

Grids, multi-clusters, NUMA systems, and ad-hoc collections of distributed computing devices all present diverse environments in which distributed computing applications can be run. Due to the diversity of features provided by these environments a distributed application that is to perform well must be specifically designed and optimised for the environment in which it is deployed. Such optimisations generally affect the application's communication structure, its consistency protocols, and its communication protocols. This thesis explores approaches to improving the ability of distributed applications to share consistent data efficiently and with improved functionality over wide-area and diverse environments. We identify a fundamental separation of concerns for distributed applications. This is used to propose a new model, called the view model, which is a hybrid, cost-conscious approach to remote data sharing. It provides the necessary mechanisms and interconnects to improve the flexibility and functionality of data sharing without defining new programming models or protocols. We employ the view model to adapt distributed applications to their run-time environment without modifying the application or inventing new consistency or communication protocols. We explore the use of view model properties on several programming models and their consistency protocols. In particular, we focus on programming models used in distributed-shared-memory middleware and applications, as these can benefit significantly from the properties of the view model. Our evaluation demonstrates the benefits, side effects and potential short-comings of the view model by comparing our model with traditional models when running distributed applications across several multi-clusters scenarios. In particular, we show that the view model improves the performance of distributed applications while reducing resource usage and communication overheads.