Doctoral School in Communication Systems
Ecole Polytechnique Fédérale de Lausanne (EPFL)
- Advisor: Professor André Schiper
- Dissertation: “Analysing RBP, a Total Order Broadcast Protocol for Unreliable Channels”
- Abstract: RBP is the acronym for Reliable Broadcast Protocol. It was published by Chang and Maxemchuck in 1984, and aims to provide total order and reliable broadcast in a distributed system subjected to process failures and fair lossy links. While the original definitions are not recent, new protocols and implementations still make use of its concepts (for example, RMP, Pinwheel and TRMP). We started our analysis by comparing RBP with another Total Order solution, the Primary Backup+VSC replication model. As View Synchronous Communication (VSC) is widely studied, it presents many techniques that can be used in order to update RBP. One of these techniques, called "two views" model is specially interesting because it allow us to take advantage from failure detectors with aggressive timeouts while minimizing the drawbacks from incorrect suspicions. Based on the analysis we ve done, we propose an improved version from the RBP protocol that uses the techniques studied in this work.
Graduate School in Computer Science
Universidade Federal do Rio Grande do Sul (UFRGS)
Porto Alegre, Brazil.
- Advisor: Professor Ingrid Jansch-Pôrto
- Dissertation: “Evaluation of Failure Detectors and their Influence on the Consensus Operations”
- Abstract: This work presents our observations and analysis on the influence of the failure detectors on the consensus algorithm. Failure detectors are essential to the consensus over an asynchronous distributed system, as they represent one of the few techniques that are able to circumvent the limitation imposed by the FLP Impossibility (the impossibility to distinguish a crashed process from a slow one, in asynchronous systems). While failure detectors are well defined through two properties, completeness and accuracy, there's no rule about their implementation. Indeed, we only found one work that tried to compare different failure detectors. Using simulation techniques, that work evaluated the impact of the failure detectors on the consensus termination time, although that research was very limited in the number of detectors analyzed and in the evaluation goals. The present work extended that experience, including more detectors in the analysis and evaluating them in a practical environment. Also, the observations were not restricted to those from the original paper, and the detectors were analyzed with more metrics, failure patterns and operational parameters. The evaluation allowed us to identify the behavior from the detectors in face of the most significant failure patterns, their influence on the consensus operation and their interaction with the execution environment. This evaluation also enabled us to compare the detectors, identifying their limitations, their best employment situations and possible optimizations to future developments.
Universidade Federal de Santa Maria (UFSM)
Santa Maria, Brazil.
- Advisor: Professor João Carlos Damasceno Lima
- Dissertation: “CsocketS - Classes para Comunicação de Rede com Autenticação e Criptografia usando Java e CORBA”
- Abstract: Security is a basic requirement for the systems developed to the Internet. The set of classes for network communications with authentication and encryption _ CsocketS _ have as goal to offer an API that could be easily integrated to the programming code from existing applications, extending the functionalities of sockets through the use of encryption, digital signature and session authentication. The system was developed using Java and CORBA, guaranteeing easiness of distribution and the interface homogeneity. We also propose a proxy architecture, enabling the handling to different applications with the use of one same server and to work through firewalls.