Search

The Ripple network is one of the most prominent blockchain platforms and its native XRP token currently has one of the highest cryptocurrency market capitalizations. The Ripple consensus protocol powers this network and is generally considered to a Byzantine fault-tolerant agreement protocol, which can reach consensus in the presence of faulty or malicious nodes. In contrast to traditional Byzantine agreement protocols, there is no global knowledge of all participating nodes in Ripple consensus; instead, each node declares a list of other nodes that it trusts and from which it considers votes. Previous work has brought up concerns about the liveness and safety of the consensus protocol under the general assumptions stated initially by Ripple, and there is currently no appropriate understanding of its workings and its properties in the literature. This paper closes this gap and makes two contributions. It first provides a detailed, abstract description of the protocol, which has been derived from the source code. Second, the paper points out that the abstract protocol may violate safety and liveness in several simple executions under relatively benign network assumptions.

Quorum systems are a key abstraction in distributed fault-tolerant computing for capturing trust assumptions. They can be found at the core of many algorithms for implementing reliable broadcasts, shared memory, consensus and other problems. This paper introduces asymmetric Byzantine quorum systems that model subjective trust. Every process is free to choose which combinations of other processes it trusts and which ones it considers faulty. Asymmetric quorum systems strictly generalize standard Byzantine quorum systems, which have only one global trust assumption for all processes. This work also presents protocols that implement abstractions of shared memory and broadcast primitives with processes prone to Byzantine faults and asymmetric trust. The model and protocols pave the way for realizing more elaborate algorithms with asymmetric trust.

This paper gives news of the last jurisdictional decision relating to the secessionist process of Quebec. Decision due to the jurisdictional body of the Superior Court of that Canadian Province, in the constitutional prosecution of a Law of the National Assembly of Quebec, known as “Loi 99”, which constituted a fully-fledged answer to the well-known Federal Government’s Clarity Act. Answer whose most notorious aspect is given by the determination in that Act that the majority needed to affirm approved by the citizens of Quebec the option of leaving Canada in a possible new referendum, is that of half plus one of the valid votes cast. The contribution of this comment to the decision of the Superior Court of Quebec consists in showing that it is not the product of an abstract reasoning about the democratic principle that it has been able to make, but of the very specific context that is given by the aforementioned Clarity Act which, in turn, it brought about the famous Advisory Opinion (or Report) issued by the Supreme Court of Canada at the request of the Federal Government after the very tight result of the second referendum on Quebec’s secessionist pretension., El texto da noticia de la última decisión jurisdiccional en relación con el proceso secesionista de Quebec. Decisión debida al órgano jurisdiccional de la Corte Superior de dicha provincia canadiense, en el enjuiciamiento constitucional de una ley de la Asamblea Nacional de Quebec, la conocida como «Loi 99», que constituyó una respuesta en toda regla a la conocida Ley de la Claridad del Gobierno federal. Respuesta cuyo aspecto sin duda más notorio viene dado por la determinación en dicha ley de que la mayoría necesaria para afirmar aprobada por los quebequeses la opción de desligarse de Canadá en una eventual nueva consulta, es la de la mitad más uno de los votos válidos emitidos. La aportación del presente comentario a la decisión de la Corte Superior quebequesa consiste en mostrar que no es producto de un razonamiento abstracto sobre el principio democrático que haya podido hacer, sino del muy específico contexto que viene dado por la citada Ley de la Claridad, que, a su vez, trajo causa de la célebre opinión consultiva (o dictamen) emanada por el Tribunal Supremo de Canadá a petición del Gobierno federal tras el muy ajustado resultado del segundo referéndum habido sobre la pretensión secesionista de Quebec.

Quorum systems are a key abstraction in distributed fault-tolerant computing for capturing trust assumptions. They can be found at the core of many algorithms for implementing reliable broadcasts, shared memory, consensus and other problems. This paper introduces asymmetric Byzantine quorum systems that model subjective trust. Every process is free to choose which combinations of other processes it trusts and which ones it considers faulty. Asymmetric quorum systems strictly generalize standard Byzantine quorum systems, which have only one global trust assumption for all processes. This work also presents protocols that implement abstractions of shared memory and broadcast primitives with processes prone to Byzantine faults and asymmetric trust. The model and protocols pave the way for realizing more elaborate algorithms with asymmetric trust.

Distributed consensus is integral to modern distributed systems. The widely adopted Paxos algorithm uses two phases, each requiring majority agreement, to reliably reach consensus. In this paper, we demonstrate that Paxos, which lies at the foundation of many production systems, is conservative. Specifically, we observe that each of the phases of Paxos may use non-intersecting quorums. Majority quorums are not necessary as intersection is required only across phases. Using this weakening of the requirements made in the original formulation, we propose Flexible Paxos, which generalizes over the Paxos algorithm to provide flexible quorums. We show that Flexible Paxos is safe, e cient and easy to utilize in existing distributed systems. We discuss far reaching implications of this result. For example, improved availability results from reducing the size of second phase quorums by one when the system size is even, while keeping majority quorums in the first phase. Another example is improved throughput of replication by using much smaller phase 2 quorums, while increasing the leader election (phase 1) quorums. Finally, non intersecting quorums in either first or second phases may enhance the efficiency of both.

Replicated systems often use quorums in order to increase their performance and availability. In such systems, a client typically accesses a quorum of the servers in order to perform an update. In this paper, we study the running time of quorum-based distributed systems over the Internet. We experiment with more than thirty servers at geographically dispersed locations; we evaluate two different approaches for defining quorums. We study how the number of servers probed by a client impacts performance and availability. We also examine the extent to which cross-correlated message loss affects the ability to predict running times accurately from end-to-end traces.

Although the United States Congress can trace its origins to British Parliament, the two institutions have evolved in significantly different directions over the past two centuries. This report provides a brief overview of the parliamentary practices in the House of Representatives and the British House of Commons focusing on such issues as membership and qualifications, the role of the Speaker and party or Government leaders, the role of committees, floor consideration, and second chambers. In a report of this length, many nuances of procedure and many rarely used parliamentary practices or traditions, both in the House of Commons and in the House of Representatives, are necessarily omitted or treated only in a cursory manner. This report will be updated as events warrant., CRS Report for Congress.

type:text, Network partition, which makes it impossible for some pairs of precesses to communicate with each other, is one of the most serious network failures. Although the notion of k-coterie is introduced to design a k-mutual exclusion algorithm robust against network failures, the number of processes allowed to simultaneously access the critical section may fatally decrease once network partition occurs. This paper discusses how to construct a k-coterie such that the k-mutual exclusion algorithm adopting it is robust against network 2-partition. To this end, we introduce the notion of complemental k-coterie, and show that complemental k-coteries meet our purpose. We then give methods for constructing complemental k-coteries, and show a necessary and sufficient condition for a k-coteries to be complemental.

Network partition, which makes it impossible for some pairs of precesses to communicate with each other, is one of the most serious network failures. Although the notion of k-coterie is introduced to design a k-mutual exclusion algorithm robust against network failures, the number of processes allowed to simultaneously access the critical section may fatally decrease once network partition occurs. This paper discusses how to construct a k-coterie such that the k-mutual exclusion algorithm adopting it is robust against network 2-partition. To this end, we introduce the notion of complemental k-coterie, and show that complemental k-coteries meet our purpose. We then give methods for constructing complemental k-coteries, and show a necessary and sufficient condition for a k-coteries to be complemental.

Network partition, which makes it impossible for some pairs of precesses to communicate with each other, is one of the most serious network failures. Although the notion of k-coterie is introduced to design a k-mutual exclusion algorithm robust against network failures, the number of processes allowed to simultaneously access the critical section may fatally decrease once network partition occurs. This paper discusses how to construct a k-coterie such that the k-mutual exclusion algorithm adopting it is robust against network 2-partition. To this end, we introduce the notion of complemental k-coterie, and show that complemental k-coteries meet our purpose. We then give methods for constructing complemental k-coteries, and show a necessary and sufficient condition for a k-coteries to be complemental.

Network partition, which makes it impossible for some pairs of precesses to communicate with each other, is one of the most serious network failures. Although the notion of k-coterie is introduced to design a k-mutual exclusion algorithm robust against network failures, the number of processes allowed to simultaneously access the critical section may fatally decrease once network partition occurs. This paper discusses how to construct a k-coterie such that the k-mutual exclusion algorithm adopting it is robust against network 2-partition. To this end, we introduce the notion of complemental k-coterie, and show that complemental k-coteries meet our purpose. We then give methods for constructing complemental k-coteries, and show a necessary and sufficient condition for a k-coteries to be complemental.