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Topic-based publish/subscribe is at the core of many distributed systems, ranging from application integration middleware to news dissemination. Therefore, much research was dedicated to publish/subscribe architectures and protocols, and in particular to the design of overlay networks for decentralized topic-based routing and efficient message dissemination. Nonetheless, existing systems fail to take full advantage of shared interests when disseminating information, hence suffering from high maintenance and traffic costs, or construct overlays that cope poorly with the scale and dynamism of large networks. In this paper, we present StaN, a decentralized protocol that optimizes the properties of gossip-based overlay networks for topic-based publish/subscribe by sharing a large number of physical connections without disrupting its logical properties. StaN relies only on local knowledge and operates by leveraging common interests among participants to improve global resource usage and promote topic and event scalability. The experimental evaluation under two real workloads, both via a real deployment and through simulation, shows that StaN provides an attractive infrastructure for scalable topic-based publish/subscribe. [ABSTRACT FROM PUBLISHER]

This paper proposes a new methodology to model the distribution of finite size content to a group of users connected through an overlay network. Our methodology describes the distribution process as a constrained stochastic graph process (CSGP), where the constraints dictated by the content distribution protocol and the characteristics of the overlay network define the interaction among nodes. A CSGP is a semi-Markov process whose state is described by the graph itself. CSGPs offer a powerful description technique that can be exploited by Monte Carlo integration methods to compute in a very efficient way not only the mean but also the full distribution of metrics such as the file download times or number of hops from the source to the receiving nodes. We model several distribution architectures based on trees and meshes as CSGPs and solve them numerically. We are able to study scenarios with a very large number of nodes and we can precisely quantify the performance differences between the tree and mesh-based distribution architectures. [ABSTRACT FROM AUTHOR]

In this paper, we present a new multicast architecture and the corresponding multicast routing protocol for providing efficient and flexible multicast services over the Internet. Traditional multicast protocols construct and update the multicast tree in a distributed manner, which may cause two problems: first, since each node has only local or partial information on the network topology and group membership, it is difficult to build an efficient multicast tree and, second, due to the lack of complete information, broadcast is often used for sending control packets and data packets, which consumes a great deal of network bandwidth. In the newly proposed multicast architecture, a few powerful routers, called m-routers, collect multicast-related information and process multicast requests based on the information collected. The m-routers handle most of the multicast-related tasks, whereas other routers in the network only need to perform minimum functions for routing. The m-routers are designed to be able to handle simultaneous many-to-many communications efficiently. The new multicast routing protocol, called the Service-Centric Multicast Protocol (SCMP), builds a shared multicast tree rooted at the m-router for each group. The multicast tree is computed in the m-router by employing the Delay-Constrained Dynamic Multicast (DCDM) algorithm, which dynamically builds a delay-constrained multicast tree and minimizes the tree cost as well. The physical construction of the multicast tree over the Internet is performed by a special type of self-routing packets in order to minimize the protocol overhead. Our simulation results on ns-2 demonstrate that the new SCMP protocol outperforms other existing protocols and is a promising alternative for providing efficient and flexible multicast services over the Internet. [ABSTRACT FROM AUTHOR]

In most existing localized topology control protocols for mobile ad hoc networks (MANETs), each node selects a few logical neighbors based on location information and uses a small transmission range to cover those logical neighbors. Transmission range reduction conserves energy and bandwidth consumption, while still maintaining network connectivity. However, the majority of these approaches assume a static network without mobility. In a mobile environment network connectivity can be compromised by two types of ‘bad’ location information: inconsistent information, which makes a node select too few logical neighbors, and outdated information, which makes a node use too small a transmission range. In this paper, we first show some issues in existing topology control. Then, we propose a mobility-sensitive topology control method that extends many existing mobility-insensitive protocols. Two mechanisms are introduced: consistent local views that avoid inconsistent information and delay and mobility management that tolerate outdated information. The effectiveness of the proposed approach is confirmed through an extensive simulation study. [ABSTRACT FROM AUTHOR]

Token Coherence is a cache coherence protocol that simultaneously captures the best attributes of the traditional approximations to coherence: direct communication between processors (like snooping-based protocols) and no reliance on bus-like interconnects (like directory-based protocols). This is possible thanks to a class of unordered requests that usually succeed in resolving the cache misses. The problem of the unordered requests is that they can cause protocol races, which prevent some misses from being resolved. To eliminate races and ensure the completion of the unresolved misses, Token Coherence uses a starvation prevention mechanism named persistent requests. This mechanism is extremely inefficient and, besides, it endangers the scalability of Token Coherence since it requires storage structures (at each node) whose size grows proportionally to the system size. While multiprocessors continue including an increasingly number of nodes, both the performance and scalability of cache coherence protocols will continue to be key aspects. In this work, we propose an alternative starvation prevention mechanism, named priority requests, that outperforms the persistent request one. This mechanism is able to reduce the application runtime more than 20 percent (on average) in a 64-processor system. Furthermore, thanks to the flexibility shown by priority requests, it is possible to drastically minimize its storage requirements, thereby improving the whole scalability of Token Coherence. Although this is achieved at the expense of a slight performance degradation, priority requests still outperform persistent requests significantly. [ABSTRACT FROM AUTHOR]