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Proof: If a correct server s executes o with sequence number i, it must have received f + 1 valid COMMIT messages for 〈o, i〉 from a quorum Q of servers. The proof is by contradiction. Suppose there is another correct server s′ that... more
Proof: If a correct server s executes o with sequence number i, it must have received f + 1 valid COMMIT messages for 〈o, i〉 from a quorum Q of servers. The proof is by contradiction. Suppose there is another correct server s′ that executes o with sequence number i′ > i. By the MinBFT algorithm, this can only happen if it receives f + 1 valid COMMIT messages for 〈o, i′〉, from a quorum Q′ of f + 1 servers. Since n = 2f + 1 and |Q|+|Q′| = 2f+2 ≥ 2f+1, there must be at least one server r (called intersection server) that sends COMMIT messages both for 〈o, i〉 and 〈o, i′〉. Assuming that the primary on view v is the server p, we have to consider four cases: 1) the primary and the intersection server are correct: in this case it is trivial to see that the primary will not generate two UI s for the same request operation o, so the intersection server will never send two valid COMMIT messages for 〈o, i〉 and 〈o, i′〉. 2) the primary is correct and the intersection server is faulty: The (fau...
The web 2.0 is transforming the project management in organizations by improving communication and collaboration. The new generation of web-based collaborative tools provides much better experience than the traditional software package... more
The web 2.0 is transforming the project management in organizations by improving communication and collaboration. The new generation of web-based collaborative tools provides much better experience than the traditional software package allowing document sharing, integrated task tracking, enforcing team processes and agile planning. Despite of the indubitable benefits brought by web 2.0, the use of these technologies to promote knowledge management remains unexplored. For many project managers to obtain and integrate information from different tools of previous similar projects in global organizations remains a challenge. This theoretical paper presents a proposal that suggests an innovation in the knowledge management area applying web 2.0 technologies. The main goal is to provide an integrated vision of a set of technologies that could be used by organizations in order to promote better management of lessons learned. The proposal includes the lessons learned processes (e.g. capture...
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Informacion presentada en el Encuentro Internacional de Vinculacion e Innovacion para el Desarrollo del sector TIC en Mexico. 29 y 30 de noviembre. Evento organizado por el CIC IPN
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Em um mercado competitivo e em constante evolução a gestão efetiva da informação e a transferência de conhecimento são aspectos estratégicos para as empresas. A fim de melhorar os processos de gestão de projetos, as empresas têm adotado... more
Em um mercado competitivo e em constante evolução a gestão efetiva da informação e a transferência de conhecimento são aspectos estratégicos para as empresas. A fim de melhorar os processos de gestão de projetos, as empresas têm adotado metodologias e frameworks, como alternativas que permitam maximizar a taxa de sucesso no desenvolvimento dos projetos. Como uma extensão da gestão de projetos, o processo de captura e análise de lições aprendidas é um método eficiente e efetivo de gestão da informação e transferência de conhecimento, adquiridos durante a execução de um projeto, permitindo que a organização aprimore seus processos, reduza custos e gere valor ao negócio. Cada projeto executado fornece uma base de conhecimento importante que pode ser utilizada como diferencial competitivo pela empresa. Este artigo teórico apresenta uma revisita e análise dos principais métodos para captura de lições aprendidas em projetos propostos nas últimas décadas. A análise foi realizada a partir d...
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Introduction Consensus is an important distributed computing problem that consists in making a set of processes agree on one of the values that each one of them proposes. Consensus in the asynchronous Byzantine message-passing model (the... more
Introduction Consensus is an important distributed computing problem that consists in making a set of processes agree on one of the values that each one of them proposes. Consensus in the asynchronous Byzantine message-passing model (the model we consider in the abstract) has been shown to require n≥ 3f+ 1 processes to be solvable in several variations of the basic system model, where f is the maximum number of faulty processes. Reducing the ratio n/f is important both theoretically, since achieving lower bounds has ...
This paper presents two asynchronous Byzantine faulttolerant state machine replication (BFT) algorithms that are minimal in several senses. First, they require only 2 f+ 1 replicas, instead of the usual 3 f+ 1. Second, the trusted service... more
This paper presents two asynchronous Byzantine faulttolerant state machine replication (BFT) algorithms that are minimal in several senses. First, they require only 2 f+ 1 replicas, instead of the usual 3 f+ 1. Second, the trusted service in which this reduction of replicas is based is arguably minimal, so it is simple to verify and implement (which is possible even using commercial trusted hardware). Third, in nice executions the two algorithms run in the minimum number of communication steps for nonspeculative and speculative algorithms, ...
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Information Technologies 2.0 (IT 2.0) is transforming the project management by improving communication and collaboration. It provides better experience than the traditional software package allowing document sharing, integrated task... more
Information Technologies 2.0 (IT 2.0) is transforming the project management by improving communication and collaboration. It provides better experience than the traditional software package allowing document sharing, integrated task tracking, enforcing team processes and agile planning. Despite the benefits brought by IT 2.0, their use to promote lessons learned (LL) remains unexplored. For many project managers to obtain and integrate information from different tools of previous similar projects remains a challenge. This chapter emphasizes the need of combining traditional LL processes and methods with IT 2.0. It describes the IT 2.0 uses and how these technologies can support LL processes and methods in project settings. It delivers a proposal focusing on both IT 2.0-centered LL processes and an updating of traditional LL methods with IT 2.0. This proposal aims to help project managers to improve the management of LL and, as a result, the project learning.
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Abstract—Modern society depends on several critical infrastructures like power, water, oil and gas generation and distribution. These infrastructures have evolved to become largely controlled by computers and interconnected by computer... more
Abstract—Modern society depends on several critical infrastructures like power, water, oil and gas generation and distribution. These infrastructures have evolved to become largely controlled by computers and interconnected by computer networks, which lets them exposed to the same types of threats as Internet systems. Therefore, research about mechanisms to improve the protection of these infrastructures is extremely important. Byzantine fault-tolerant (BFT) replication algorithms tackle this problem by allowing critical services, like storage ...
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are stored in PDF, with the report number as filename. Alternatively, reports are available by post from the above address.
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Abstract—The popularity of wide-area computer services has generated a compelling need for efficient algorithms that provide high reliability. Byzantine fault-tolerant (BFT) algorithms can be used with this purpose because they allow... more
Abstract—The popularity of wide-area computer services has generated a compelling need for efficient algorithms that provide high reliability. Byzantine fault-tolerant (BFT) algorithms can be used with this purpose because they allow replicated systems to continue to provide a correct service even when some of their replicas fail arbitrarily, either accidentally or due to malicious faults. Current BFT algorithms perform well on LANs but when the replicas are distributed geographically their performance is affected by the lower bandwidth and the higher and more heterogeneous network latencies. This paper proposes and evaluates a novel BFT algorithm for WANs that requires fewer communication steps, fewer replicas and has better throughput and latency than others in the literature. The paper presents an extensive evaluation of the algorithm’s performance in several settings and conditions: in a LAN; in real and emulated WANs; with clients close to servers and dispersed geographically; ...
Abstract—The popularity of wide-area computer services has generated a compelling need for efficient algorithms that provide high reliability. Byzantine fault-tolerant (BFT) algorithms can be used with this purpose because they allow... more
Abstract—The popularity of wide-area computer services has generated a compelling need for efficient algorithms that provide high reliability. Byzantine fault-tolerant (BFT) algorithms can be used with this purpose because they allow replicated systems to continue to provide a correct service even when some of their replicas fail arbitrarily, either accidentally or due to malicious faults. Current BFT algorithms perform well on LANs but when the replicas are distributed geographically their performance is affected by the lower bandwidth and the ...
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Most Byzantine fault-tolerant state machine replication (BFT) algorithms have a primary replica that is in charge of ordering the clients requests. Recently it was shown that this dependence allows a faulty primary to degrade the... more
Most Byzantine fault-tolerant state machine replication (BFT) algorithms have a primary replica that is in charge of ordering the clients requests. Recently it was shown that this dependence allows a faulty primary to degrade the performance of the system to a small fraction of what the environment allows. In this paper we present Spinning, a novel BFT algorithm that mitigates such performance attacks by changing the primary after every batch of pending requests is accepted for execution. This novel mode of operation deals with ...
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Intrusion tolerance has been proposed as a new paradigm for computer systems security. The idea is to apply the fault tolerance paradigm in the domain of systems security accepting that malicious faults (attacks, intrusions) can never be... more
Intrusion tolerance has been proposed as a new paradigm for computer systems security. The idea is to apply the fault tolerance paradigm in the domain of systems security accepting that malicious faults (attacks, intrusions) can never be entirely prevented, and that highly resilient systems have to tolerate these faults. Research in this area has produced a set of clever intrusion-tolerant protocols and systems (I/T protocols and I/T systems for short). However, we believe that an issue has been overlooked: that servers have, finite memory, ...
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This paper presents two Byzantine fault-tolerant state machine replication (BFT) algorithms that are minimal in several senses. First, they require only 2 f+ 1 replicas, instead of the usual 3 f+ 1. Second, the trusted service in which... more
This paper presents two Byzantine fault-tolerant state machine replication (BFT) algorithms that are minimal in several senses. First, they require only 2 f+ 1 replicas, instead of the usual 3 f+ 1. Second, the trusted service in which this reduction of replicas is based is arguably minimal: it provides an interface with a single function and is composed only by a counter and a signature generation primitive. Third, in nice executions the two algorithms run in the minimum number of communication steps for non-speculative and speculative ...