Special Issue: Performance evaluation of communications in distributed systems and Web based service architectures

Taha et al. [1] evaluate the consequence of choosing a frame structure type in Worldwide Interoperability for Microwave Access (WiMAX) networks based non-transparent relay stations (ntRS). In the IEEE (Institute of Electrical and Electronics Engineers) 802.16j-2009 protocol, two frame structure types are possible: single frame and multi frame. From performance evaluation point of view, a comparison has never been investigated. The authors suggest to expand on Light WiMAX ns2 add-on to support ntRS, the two frame structure types, in addition to the relevant operational requirements [e.g., quality of service (QoS)]. They show that the multi-frame structure allows higher throughput and voice capacities whereas the single frame shows some general advantage in terms of delay. De Grandia et al. [2] focus on the extension of the high level architecture (HLA) standard with balancing techniques to be used during simulation. The authors studied some balancing approaches to provide a sub-optimal solution for the imbalance issues. But, these approaches are limited to some simulation aspects. Also, a hierarchical balancing scheme was proposed that presents several drawbacks that are related to the centralization of the core part of the scheme, the redistribution algorithm, which is susceptible to bottlenecks, overheads, global synchronization, and single point of failure. Therefore, a scheme based on a distributed algorithm to rearrange the computational and communication load dynamically is proposed. Experiments have been performed to evaluate the effectiveness of the distributed scheme when compared with the scheme based on a centralized redistribution algorithm. The experimental results show that the distributed balancing technique can provide balancing efficiency similar to the centralized technique or even improve the performance gain for some specific cases. Gidenstam et al. [3] propose the cluster consistency model that bridges the gap between traditional and current approaches in supporting both scalability and ordered event delivery. The study introduces 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 decentralized probabilistic protocols supporting scalable group communication. This paper provides analytical and experimental evaluation of the properties regarding the fault tolerance of the approach. Anderson [4] shows that the combination of various methods for information research significantly enhance the search results. The author explores context data, using query enhancement techniques, and appropriately fusing the results to provide the best ordering when presenting the results to the user. Context data includes a users personal calendar, location, preferences, personal vocabulary, and peer recommendations. Query enhancement involves utilizing relevant contextual information to decorate a users query text to produce a more focused query. Information fusion allows the query results to be compared and re-ordered using contextual data by utilizing either a sum of products, a Bayesian technique, or a combination of the two. Finally, she has performed a case study. Othman and Saavedra [5] describe IBCHWMP, a secure Hybrid-Wireless-Mesh Protocol (HWMP) using Identity Based Cryptography (IBC) over the IEEE P802.11s/D4.0 protocol. IBC has been used because it does not need to verify the authenticity of public keys. IBC mechanism has implemented to secure control messages in HWMP, namely Path Request and Path Reply. Authors focus on secure data exchange in mutable fields. Through extensive ns-3 simulations, results show that the overhead introduced by IBC-HWMP is not significant compared with the classical HWMP. Brust et al. [6] present a novel and scalable approach for positioning of mobile sensor nodes with the goal of monitoring the Amazon river. The actors in the scenario are stationary and positioned