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Capsule Reviews

Kamareddine, F. — 2009-06-10

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.

Guest Editorial

Katsaggelos, A. K., Molina, R. — 2009-06-10

Aggregation Dynamics in Overlay Networks and Their Implications for Self-Organized Distributed Applications

Saffre, F., Tateson, R., Halloy, J., Shackleton, M., Deneubourg, J. L. — 2009-06-10

In this paper, we investigate the global self-aggregation dynamics arising from local decision-based rewiring of an overlay network, used as an abstraction for an autonomic service-oriented architecture. We measure the ability of a selected set of local rules to foster self-organization of what is originally a random graph into a structured network. Scalability issues with respect to the key parameters of system size and diversity are extensively discussed. Conflicting goals are introduced, in the form of a population of nodes actively seeking to acquire neighbours of a type different from their own, resulting in decreased local homogeneity. We show that a ‘secondary’ self-organization process ensues, whereby nodes spontaneously cluster according to their implicit objective. Finally, we introduce dynamic goals by making the preferred neighbour type a function of the local characteristics of a simulated workload. We demonstrate that in this context, an overlay rewiring process based purely on local decisions and interactions can result in efficient load-balancing without central planning. We conclude by discussing the implications of our findings for the design of future distributed applications, the likely influence of other factors and of extreme parameter values on the ability of the system to self-organize and the potential improvements to our framework.

Dynamic Selection of a Video Content Adaptation Strategy from a Pareto Front

Sofokleous, A. A., Angelides, M. C. — 2009-06-10

Genetic Algorithms may be used together with Pareto Optimality in the process of selection of a suitable video content adaptation strategy, the former to return best or fittest solutions that have evolved over many generations and the latter to evaluate and rank each generation's solutions against a set of objectives without the need to assign weights to each one. The outcome of this is a Pareto front of optimal strategies, all of which would satisfy the objectives. The distribution of optimal strategies on a Pareto front, however, suggests that there may be a ‘best-fit’ optimal strategy. This article refines the process of selection of an optimal strategy by taking into account this distribution alongside user preferences, video content characteristics and usage history. In order to make the refined process dynamic, it pursues its implementation using Self-Organising Neural Networks.

A Pragmatic Methodology for Testing Intrusion Prevention Systems

Chen, Z., Delis, A., Wei, P. — 2009-06-10

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 IUT's 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.

A Location Prediction-Based Reactive Routing Protocol to Minimize the Number of Route Discoveries and Hop Count per Path in Mobile Ad Hoc Networks

Meghanathan, N. — 2009-06-10

We propose a new mobile ad hoc network routing protocol called ‘location prediction-based routing’ (LPBR) to simultaneously minimize the number of route discoveries and hop count of the paths for a source–destination session. During a regular flooding-based route discovery, LPBR collects the location and mobility information of nodes in the network and stores the collected information at the destination node of the route search process. When the minimum hop route discovered through the flooding-based route discovery fails, the destination node attempts to predict the current location of each node using the location and mobility information collected during the latest flooding-based route discovery. A minimum hop Dijkstra algorithm is run on the locally predicted global topology. If the predicted minimum hop route exists in reality, no expensive flooding-based route discovery is needed and the source continues to send data packets on the discovered route; otherwise, the source initiates another flooding-based route discovery. Simulation results indicate that LPBR incurs a significantly reduced number of flooding-based route discoveries, lower hop count per path, smaller route discovery overhead, lower end-to-end delay per packet and higher packet delivery ratio compared with that of the minimum hop-based, stability-based and position-based routing protocols.

Preserving the Fault-Containment of Ring Protocols Executed on Trees

Yamauchi, Y., Masuzawa, T., Bein, D. — 2009-06-10

Reliable and fault-tolerant distributed systems have been attracting more and more attention (see Autonomic Computing Project by IBM, http://www-03.ibm.com/autonomic/). A self-stabilizing protocol is a fault-tolerant protocol that guarantees autonomous recovery from any number of and any type of faults that can affect the data stored locally at some process(es). If the impact of the faults can be contained to the affected process(es) and some of its immediate neighbors, then the protocol is also fault-containing. We present a new method, called causal simulation, which preserves the fault-containing property of ring protocols executed on trees.

The Agreement Problem in Unreliable Scale-Free Networks

Yan, K.-Q., Wang, S.-S., Wang, S.-C. — 2009-06-10

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.

TRACEY HO AND DESMOND S. LUN * Network Coding: An Introduction. Cambridge University Press (2008). ISBN 9780521873109. 184 pp. {pound}30/$60. Hardcover.

Geil, O. — 2009-06-10

JOHN E. GIBSON, WILLIAM T. SCHERER AND WILLIAM F. GIBSON * How to do Systems Analysis. Wiley (2007). ISBN-13: 978-0-470-00765-5. {pound}47.50. 360 pp. Hardcover.

Harrin, E. — 2009-06-10