Naming is of fundamental importance in the design of transparently distributed operating systems. A transparently distributed operating system should be functionally equivalent to the systems of which it is composed. In particular, the names of remote objects should be indistinguishable from the names oflocal objects. In this thesis we explore the implication that this recursive notion of transparency has for the naming mechanisms provided by an operating system. In particular, we show that a recursive naming system is more readily extensible than a flat naming system by demonstrating that it is in precisely those areas in which a system is not recursive that transparency is hardest to achieve. However, this is not so much a problem of distribution so much as a problem of scale. A system which does not scale well internally will not extend well to a distributed system. Building a distributed system out of existing systems involves joining the name spaces of the individual systems together. When combining name spaces it is important to preserve the identity of individual objects. Although unique identifiers may be used to distinguish objects within a single name space, we argue that it is difficult if not impossible in practice to guarantee the uniqueness of such identifiers between name spaces. Instead, we explore the possibility of Using hierarchical identifiers, unique only within a localised context. However, We show that such identifiers cannot be used in an arbitrary naming graph without compromising the notion of identity and hence violating the semantics of the underlying system. The only alternative is to sacrifice a deterministic notion of identity by using random identifiers to approximate global uniqueness with a know probability of failure (which can be made arbitrarily small if the overall size of the system is known in advance).

A computation model for distributed systems which has found widespread acceptance is that of atomic actions (atomic transactions) controlling operations on persistent objects. Much current research work is oriented towards the design and implementation of distributed systems supporting such an object and action model. However, little work has been done to investigate the suitability of such a model for building reliable distributed systems. Atomic actions have many properties which are desirable when constructing reliable distributed applications, but these same properties can also prove to be obstructive. This thesis examines the suitability of atomic actions for building reliable distributed applications. Several new structuring techniques are proposed providing more flexibility than hitherto possible for building a large class of applications. The proposed new structuring techniques are: Serialising Actions, Top-Level Independent Actions, N-Level Independent Actions, Common Actions and Glued Actions. A new generic form of action is also proposed, the Coloured Actions, which provides more control over concurrency and recovery than traditional actions. It will be shown that Coloured Actions provide a uniform mechanism for implementing most of the new structuring techniques, and at the same time are no harder to implement than normal actions. Thus this proposal is of practical importance. The suitability of new structuring techniques will be demonstrated by considering a number of applications. It will be shown that the proposed techniques provide natural tools for composing distributed applications.

Conventional studies in communication networks mostly focus on securely and reliably transmitting  data from a source node (or multiple source nodes) to multiple destinations. A more general problem appears when the destination nodes are interested in obtaining  functions of the data available in distributed source nodes. For obtaining a function, transmitting all the data to a destination node and then computing the function might be inefficient. In order to exploit the network resources efficiently, the general problem offers distributed computing in combination with coding and communication. This problem has applications in distributed systems, e.g., in wireless sensor networks, in distributed storage systems, and in distributed computing systems. Following this general problem formulation, we study the optimal and secure recovery of the lost data in storage nodes and in reconstructing a version of a file in distributed storage systems.   The significance of this study is due to the fact that the new trends in communications including big data, Internet of things, low latency, and high reliability communications challenge the existing centralized data storage systems. Distributed storage systems can rectify those issues by  distributing  thousands of storage nodes (possibly around the globe), and then benefiting users by bringing data to their proximity.  Yet, distributing the storage nodes brings new challenges. In these distributed systems, where storage nodes  are connected through links and servers, communication plays a main role in their performance. In addition,  a part of network may fail or due to communication failure or delay there might exist multi versions of a file. Moreover, an intruder can overhear the communications between storage nodes and obtain some information about the stored data. Therefore, there are challenges on  reliability, security, availability, and consistency.   To increase reliability, systems need to store redundant data in storage nodes and employ error control codes. To maintain the  reliability  in a dynamic environment where storage nodes can fail, the system should have an autonomous repair process. Namely, it should regenerate the failed nodes by the help of other storage nodes. The repair process demands bandwidth, energy, or in general transmission costs.  We propose novel techniques to reduce the repair cost in distributed storage systems.   First, we propose {surviving nodes cooperation} in repair, meaning that surviving nodes can combine their received data with their own stored data and then transmit toward the new node. In addition, we study the repair problem in multi-hop networks and consider the cost of transmitting data between storage nodes.  While classical repair model assumes the availability of direct links between the new node and surviving nodes, we consider that such links may not be available either due to failure or their costs.  We formulate an optimization problem to minimize the repair cost and compare two systems, namely with and without surviving nodes cooperation.   Second, we study the repair problem where the links between storage nodes are lossy e.g., due to server congestion, load balancing, or unreliable physical layer (wireless links).  We model the lossy links by packet erasure channels and then derive the fundamental bandwidth-storage tradeoff in packet erasure networks. In addition, we propose dedicated-for-repair storage nodes to reduce the repair-bandwidth.   Third, we generalize the repair model by proposing the concept of partial repair. That is, storage nodes may lose parts of their stored data. Then in partial repair, the lost data is recovered by exchanging data between storage nodes and using the available data in storage nodes as side information. For efficient partial-repair,  we propose two-layer coding in distributed storage systems and then we derive the optimal bandwidth in partial repair.   Fourth, we study security in distributed storage systems.  We investigate security in partial repair. In particular, we propose codes that make the partial repair secure in the senses of strong and weak information-theoretic security definitions.   Finally, we study consistency in distributed storage systems. Consistency means that distinct users obtain the latest version of a file in a system that stores multi versions of a file. Given the probability of receiving a version by a storage node and the constraint on the node storage space, we aim to find the optimal encoding of multi versions of a file that maximizes the probability of obtaining the latest version of a file or a version close to the latest version by a read client that connects to a number of storage nodes. / <p>Pages 153-168 are removed due to copyright reasons.</p><p>QC 20161012</p><p></p>

Este trabalho de mestrado propõe uma plataforma para o desenvolvimento e a execução de aplicações distribuídas em grids computacionais. Tal plataforma visa simplificar o desenvolvimento dessas aplicações, ao mesmo tempo em que as torna capazes de usar recursos compartilhados em um grid. No esquema proposto, o ambiente de desenvolvimento do grid tem estreito relacionamento com o próprio grid, na medida em que o grid distribui a execução dos programas gerados pelo ambiente de desenvolvimento de forma automática. Além de definir a forma de desenvolver as aplicações, o presente trabalho de mestrado também propõe uma infra-estrutura para grids composta por um sistema de troca de mensagens, um escalonador baseado na teoria fuzzy e um mecanismo simples de persistência distribuída. / This thesis proposes a platform for computational grids distributed applications development and execution. The purpose of this platform is to simplify the development of such applications while delivering access to shared resources in a grid environment. In the proposed schema, the grid development environment has a close link with the grid itself as the grid distributes the execution of programs created by the development environment in an automated fashion. Besides presenting a way to develop applications, this thesis also proposes a grid infrastructure composed by a message system, a job scheduler based on fuzzy theory and a simple mechanism of distributed persistence.

Este trabalho de mestrado propõe uma plataforma para o desenvolvimento e a execução de aplicações distribuídas em grids computacionais. Tal plataforma visa simplificar o desenvolvimento dessas aplicações, ao mesmo tempo em que as torna capazes de usar recursos compartilhados em um grid. No esquema proposto, o ambiente de desenvolvimento do grid tem estreito relacionamento com o próprio grid, na medida em que o grid distribui a execução dos programas gerados pelo ambiente de desenvolvimento de forma automática. Além de definir a forma de desenvolver as aplicações, o presente trabalho de mestrado também propõe uma infra-estrutura para grids composta por um sistema de troca de mensagens, um escalonador baseado na teoria fuzzy e um mecanismo simples de persistência distribuída. / This thesis proposes a platform for computational grids distributed applications development and execution. The purpose of this platform is to simplify the development of such applications while delivering access to shared resources in a grid environment. In the proposed schema, the grid development environment has a close link with the grid itself as the grid distributes the execution of programs created by the development environment in an automated fashion. Besides presenting a way to develop applications, this thesis also proposes a grid infrastructure composed by a message system, a job scheduler based on fuzzy theory and a simple mechanism of distributed persistence.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / A distributed architecture framework has been developed for NASA at Goddard Space Flight Center (GSFC) as the basis for developing an extended series of space mission support data systems. The architecture is designed to include both mission development and operations. It specifically addresses the problems of standardizing a framework for which commercial off-the-shelf (COTS) applications and infrastructure are expected to provide most of the components of the systems. The resulting distributed architecture is developed based on a combination of a layered architecture, and carefully selected open standards. The layering provides the needed flexibility in mission design to support the wide variability of mission requirements. The standards are selected to address the most important interfaces, while not over constraining the implementation options.

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