Scalable group communication supporting configurable levels of consistency

Group communication is deployed in many evolving Internet-scale cooperative applications such as multiplayer online games and virtual worlds to efficiently support interaction on information relevant to a potentially very large number of users or objects. Especially peer-to-peer based group communication protocols have evolved as a promising approach to allow intercommunication between many distributed peers. Yet, the delivery semantics of robust and scalable protocols such as gossiping is not sufficient to support consistency semantics beyond eventual consistency because no relationship on the order of events is enforced. On the other hand, traditional consistency models provided by reliable group communication providing causal or even total order are restricted to support only small groups.This article proposes the cluster consistency model which bridges the gap between traditional and current approaches in supporting both scalability and ordered event delivery. We introduce a dynamic and fault tolerant cluster management method that can coordinate concurrent access to resources in a peer-to-peer system and can be used to establish fault-tolerant configurable cluster consistency with predictable reliability, running on top of decentralised probabilistic protocols supporting scalable group communication. This is achieved by a general two-layered architecture that can be applied on top of the standard Internet communication layers and offers a modular, layered set of services to the applications that need them. Further, we present a fault-tolerant method implementing causal cluster consistency with predictable reliability, running on top of decentralised probabilistic protocols supporting group communication.This paper provides analytical and experimental evaluation of the properties regarding the fault tolerance of the approach. Furthermore, our experimental study, conducted by implementing and evaluating the two-layered architecture on top of standard Internet transport services, shows that the approach scales well, imposes an even load on the system, and provides high-probability reliability guarantees

Foreword

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Scalable group communication supporting configurable levels of consistency

Group communication is deployed in many evolving Internet-scale cooperative applications such as multiplayer online games and virtual worlds to efficiently support interaction on information relevant to a potentially very large number of users or objects. Especially peer-to-peer based group communication protocols have evolved as a promising approach to allow intercommunication between many distributed peers. Yet, the delivery semantics of robust and scalable protocols such as gossiping is not sufficient to support consistency semantics beyond eventual consistency because no relationship on the order of events is enforced. On the other hand, traditional consistency models provided by reliable group communication providing causal or even total order are restricted to support only small groups.This article proposes the cluster consistency model which bridges the gap between traditional and current approaches in supporting both scalability and ordered event delivery. We introduce a dynamic and fault tolerant cluster management method that can coordinate concurrent access to resources in a peer-to-peer system and can be used to establish fault-tolerant configurable cluster consistency with predictable reliability, running on top of decentralised probabilistic protocols supporting scalable group communication. This is achieved by a general two-layered architecture that can be applied on top of the standard Internet communication layers and offers a modular, layered set of services to the applications that need them. Further, we present a fault-tolerant method implementing causal cluster consistency with predictable reliability, running on top of decentralised probabilistic protocols supporting group communication.This paper provides analytical and experimental evaluation of the properties regarding the fault tolerance of the approach. Furthermore, our experimental study, conducted by implementing and evaluating the two-layered architecture on top of standard Internet transport services, shows that the approach scales well, imposes an even load on the system, and provides high-probability reliability guarantees

Design of a backup network for catastrophe scenarios

Communication networks play a fundamental role in the response to a massive catastrophe, like an earthquake or a large-scale terrorist attack to a major urban area. In such situations, command centres must be able to rely on a fully operational communication network, for example to learn about on-going situations and allocate and guide the rescue teams. Communication is bidirectional: once in the field, these teams will feed the command centre with a more accurate view of the situation, contributing to the efficient allocation of the resources. Failures in this network, even if localised to some of the regions affected by the catastrophe, can have costs both monetary and in human lives. In this position paper, we propose the creation of a redundant, best-effort, emergency communication network that could serve to mitigate localised failures using off-the-shelf widespread technology. We give an overview of an architecture for a backup network, highlight the possible advantage of such an architecture to disaster management and discuss challenges that need to be overcome in realising it

Lightweight Causal Cluster Consistency

Within an effort for providing a layered architecture of services supporting multi-peer collaborative applications, this paper proposes a new type of consistency management aimed for applications where a large number of processes share a large set of replicated objects. Many such applications, like peer-to-peer collaborative environments for training or entertaining purposes, platforms for distributed monitoring and tuning of networks, rely on a fast propagation of updates on objects, however they also require a notion of consistent state update. To cope with these requirements and also ensure scalability, we propose the cluster consistency model. We also propose a two-layered architecture for providing cluster consistency. This is a general architecture that can be applied on top of the standard Internet communication layers and offers a modular, layered set of services to the applications that need them. Further, we present a fault-tolerant protocol implementing causal cluster consistency with predictable reliability, running on top of decentralised probabilistic protocols supporting group communication. Our experimental study, conducted by implementing and evaluating the two-layered architecture on top of standard Internet transport services, shows that the approach scales well, imposes an even load on the system, and provides high-probability reliability guarantees