by providing the design and performance study of one of the major problems in this domain: consensus. Recently, this problem has been redefined – by taking into account the dynamic nature of self-organizing networks – and has been renamed FT-CUP (fault tolerant consensus with unknown participants). Our work

-Widmayer impossibility results, which is achieved through randomization. Finally, the protocol was prototyped and subject to a comparative performance evaluation against two well-known Byzantine fault-tolerant consensus protocols. The results show that, due to its design, Turquois outperforms the other protocols by more

We consider the consensus problem in asynchronous models enriched with unreliable failure detectors or partial synchrony, where processes can crash or links may fail by losing messages.

This work was partially supported by: CE through project FP7-257475 (MASSIF) FCT through the multianual program (LaSIGE) PTDC/EIA-EIA/113729/2009 (SITAN) Acknowledgments First, I would like to thank my advisor, prof. Nuno Neves, for accepting me as his student, helping me with every issue I faced during the research period, establish a high bar for every task assigned to me, improving the overall quality of my work and for his patience in clarifying every question I had. I want to acknowledge Faculty of Sciences, particularly the Department of Informa-tics. During this years I had the opportunity to learn so much, acquire lots of good ex-periences, met good colleagues and Professors who were very helpful in every issue I faced. I also want to thank the Navigators research team for their welcoming, support and fellowship. I also want to thank my close friends for the moral support and company during hard

T occurs. Fault-tolerant consensus protocols are given for various cases of partial synchrony and various fault models. Lower bounds that show in most cases that our protocols are optimal with respect to the number of faults tolerated are also given. Our consensus protocols for partially synchronous

We derive lower bounds on the number of messages and the number of message delays required by a nonblocking fault-tolerant consensus algorithm, and we show that variants of the Paxos algorithm achieve those bounds.

A fault-tolerant system is one that can sustain a reasonable number of process or communication failures, both intermittent and permanent. The ability to

). We show that this parameterized two-step consensus protocol is also optimal in terms of both number of communication steps, and number of processes. Index Terms — Distributed systems, Byzantine fault tolerance, Consensus

, for achieving fault-tolerance in collaborative target detection algorithms. In value-fusion, sensor devices first exchange their measured values to arrive at a fault-tolerant consensus on the measurement. Then each device makes an independent decision as to whether or not a target is present based

We consider the fault-tolerant consensus problem in radio networks with crash-prone nodes. Specifically, we develop lower bounds and matching upper bounds for this problem in single-hop radios networks, where all nodes are located within broadcast range of each other. In a novel break from