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Generally, tasks in a distributed system must reach agreement. This requires a set of processors to agree on a common value even though some components may be corrupt. There have been several significant studies on this agreement problem in regularized network environments such as the fully connected, broadcast and multicast networks. Recently, many large complex networks have emerged displaying a scale-free feature that influences the system to reach a common value in a novel way. This unanimity problem is called Byzantine agreement (BA). The BA problem is one of the most significant problems in designing a fault-tolerant distributed system. Unfortunately, existing BA protocols cannot cope with the new network environment, and the BA problem thus must be revisited. In this paper, a new BA protocol is proposed that adapts to the scale-free network (SFN) environment and derives its limit of allowable faulty components while maintaining the minimum number of message exchanges. The correctness and complexity of this protocol have been proved. It is observed that an SFN in conjunction with the proposed agreement protocol can tolerate the maximum number of faulty components. [ABSTRACT FROM AUTHOR]

Intrusion prevention systems (IPSs) not only attempt to detect attacks but also block malicious traffic and pro-actively tear down pertinent network connections. To effectively thwart attacks, IPSs have to operate both in real-time and inline fashion. This dual mode renders the design/implementation and more importantly the testing of IPSs a challenge. In this paper, we propose an IPS testing framework termed IPS Evaluator which consists of a trace-driven inline simulator-engine, mechanisms for generating and manipulating test cases, and a comprehensive series of test procedures. The engine features attacker and victim interfaces which bind to the external and internal ports of an IPS-under-testing (IUT). Our engine employs a bi-directional injection policy to ensure that replayed packets are subject to security inspection by the IUT before they are forwarded. Furthermore, the send-and-receive mechanism of our engine allows for the correlation of engine-replayed and IUT-forwarded packets as well as the verification of IUT actions on detected attacks. Using dynamic addressing and routing techniques, our framework rewrites both source and destination addresses for every replayed packet on-the-fly. In this way, replayed packets conform to the specific features of the IUT. We propose algorithms to partition attacker/victim-emanated packets so that they are subjected to security inspections by the IUT and in addition, we offer packet manipulation operations to shape replayed traces. We discuss procedures that help verify the IUTs detection and prevention accuracy, attack coverage and behavior under diverse traffic patterns. Finally, we evaluate the strengths of our framework by mainly examining the open-source IPS Snort-Inline. IPS deficiencies revealed during testing help establish the effectiveness of our approach. [ABSTRACT FROM AUTHOR]

The Capsule Reviews are intended to provide a short succinct review of each paper in the issue in order to bring to a wider readership. The Capsule Reviews were compiled by Fairouz Kamareddine. Professor Kamareddine is an Associate Editor of The Computer Journal and is based in the Department of Mathematical and Computer Sciences at Heriot-Watt University, Edinburgh, UK. [ABSTRACT FROM AUTHOR]

The Capsule Reviews are intended to provide a short succinct review of each paper in the issue in order to bring to a wider readership. The Capsule Reviews were compiled by Fairouz Kamareddine. Professor Kamareddine is an Associate Editor of The Computer Journal and is based in the Department of Mathematical and Computer Sciences at Heriot-Watt University, Edinburgh, UK. [ABSTRACT FROM AUTHOR]

We describe the Snob program for unsupervised learning as it has evolved from its beginning in the 1960s until its present form. Snob uses the minimum message length principle expounded in Wallace and Freeman (Wallace, C.S. and Freeman, P.R. (1987) Estimation and inference by Compact coding. J. Roy. Statist. Soc. Ser. B, 49, 240–252.) and we indicate how Snob estimates class parameters using the approach of that paper. We will survey the evolution of Snob from these beginnings to the state that it has reached as described by Wallace and Dowe (Wallace, C.S. and Dowe, D.L. (2000) MMM mixture modelling of multi-state, Poisson, Von Mises Circular and Gaussian distributions. Stat. Comput., 10, 73–83.) We pay particular attention to the revision of Snob in the 1980s where definite assignment of things to classes was abandoned. [ABSTRACT FROM AUTHOR]

The Walnut kernel is a capability-based operating system kernel that was developed in the Department of Computer Science at Monash University during the 1990s. This kernel is heir to many of the ideas that were implemented in the Password- Capability System. Focusing on the programmers view, this paper describes the password-capability model and the features of the Walnut kernel and the design decisions taken in creating it. An ANSI compliant standard I/O library is used as an example of the expressive power of the system. [ABSTRACT FROM AUTHOR]

Approximation algorithms and parameterized complexity are usually considered to be two separate ways of dealing with hard algorithmic problems. In this paper, our aim is to investigate how these two fields can be combined to achieve better algorithms than what any of the two theories could offer. We discuss the different ways parameterized complexity can be extended to approximation algorithms, survey results of this type and propose directions for future research. [ABSTRACT FROM AUTHOR]

The Capsule Reviews are intended to provide a short succinct review of each paper in the issue in order to bring the content to a wider readership. The Capsule Reviews were compiled by Fairouz Kamareddine. Professor Kamareddine is an Associate Editor of The Computer Journal and is based in the Department of Mathematical and Computer Science at Heriot-Watt University, Edinburgh, UK. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of the InfiniBand link layer with special efforts made for packet latency reduction and buffer space optimization. The link layer is designed to avoid any architectural conflict while its components are executed in parallel as far as possible. For high-speed packet processing with the various quality of service supports required by InfiniBand, three candidates for packet receiving architecture are investigated. The maximum and minimum delays from an input to an output of a switch adopting each of the three candidates is estimated by mathematically modeling the switch delays. Then, the candidate architecture with the best performance is chosen, and a novel first-in first-out (FIFO) is designed to efficiently implement the chosen architecture. Simulation results show that the chosen architecture achieves the least packet latency and uses the least memory space among the three candidates. The link layer core is implemented in an InfiniBand host channel adapter system-on-chip called KINCA. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of boundary fill of a 4 or 8-connected region in a graphic device having a color image frame-buffer memory. We provide an algorithm that solves the problem in a time linear in the number of pixels in the region and requiring only constant memory space in addition to the frame-buffer memory itself. We map this problem to a boundary fill problem in a general graph, and solve it using a novel depth first search-based algorithm. [ABSTRACT FROM AUTHOR]

The Capsule Reviews are intended to provide a short succinct review of each paper in the issue in order to bring the content to a wider readership. The Capsule Reviews were compiled by Fairouz Kamareddine. Professor Kamareddine is an Associate Editor of The Computer Journal and is based in the Department of Mathematical and Computer Sciences at Heriot-Watt University, Edinburgh, UK. [ABSTRACT FROM AUTHOR]

In mobile environments, transmitting information relevant to an event along with notification of the event has been proven to be an effective means of providing revenue enhancing services. For example, a relevant advertisement can be displayed just before event notification; for instance, a product promotion by Beckham can be shown just before the notification of a goal scored by him. Challenges in achieving real-time search and delivery of information relevant to events as they occur include: (i) predicting the next event so that the appropriate information can be kept ready; (ii) finding information relevant to the context and content of the event; (iii) searching for and bringing the potentially needed information closer to the user location; and (iv) disseminating and displaying relevant information just before the actual event is notified to the user. In this paper, we propose a real-time information delivery system based on an events context and content. The key features of our system are: (i) representing domains with event-based scenarios using statecharts; (ii) using a novel combination of history information and state transitions to predict events; and (iii) real-time delivery of information relevant to an event by prefetching and caching information based on the events predicted to occur in the near future. To illustrate our approach, we focus on the delivery of advertisements relevant to notified events as a specific case of delivery of information relevant to the events. Using an experimental setup, we measured the effectiveness of our approach as compared to a context-unaware approach to event prediction. Experiments demonstrate that our approach has a superior performance, resulting in: (i) better prediction accuracy; (ii) the delivery of the most relevant information most of the time; and (iii) an effective cache management in mobile devices. [ABSTRACT FROM AUTHOR]

Recently many scalable and efficient solutions for event dissemination in publish/subscribe (pub/sub) systems have appeared in the literature. This dissemination is usually done over an overlay network of brokers and its cost can be measured as the number of messages sent over the overlay to allow the event to reach all intended subscribers. Efficient solutions to this problem are often obtained through smart dissemination algorithms that avoid flooding events on the overlay. In this paper, we propose a complementary approach that obtains efficient event dissemination by reorganizing the overlay network topology. More specifically, this reorganization is done through a self-organizing algorithm executed by brokers whose aim is to directly connect, through overlay links, pairs of brokers matching same events. In this way, on average, the number of brokers involved in an event dissemination decreases, thus reducing its cost. Even though the paradigm of the self-organizing algorithm is general and then applicable to any overlay-based pub/sub system, its concrete implementation depends on the specific system. As a consequence, we studied the effect of the introduction of the self-organizing algorithm in the context of a specific system implementing a tree-based routing strategy, namely SIENA, showing the actual performance benefits through an extensive simulation study. In particular, performance results point out the capacity of the algorithm to converge to an overlay topology accommodating efficient event with respect to (w.r.t) dissemination a specific scenario. Moreover, the algorithm shows a significant capacity to adapt the overlay network topology to continuously changing scenarios while keeping an efficient behavior w.r.t. event dissemination. [ABSTRACT FROM AUTHOR]