This paper details a concept model for proactive competence, that provides a bridge between Situational Awareness (SA) and Operational Agility (OA) models. The model addresses a gap within the literature for an end-to-end view of the functions required for effective awareness and proactive action. A set of common concepts from different SA-domains are defined to provide a consistent approach and improve the interface of models implemented across different domains. An abstract OA model is developed and the concepts defined, as there lacks an underpinning theory within agility literature. Cybernetic principles are applied to ensure the viability of the model as a potential blueprint for the design of system architecture and provide a measure of underpinning theory to SA and OA models that has been lacking from existing approaches. The Viable System Model (VSM) provides the framework upon which to develop the concept model and demonstrate how a cybernetic approach may contribute to SA and OA literature.

Wireless links are typically modeled in isolation as independent and parallel links. However, in reality, there is often a correlation in defects and impairments between collocated links. The spatial correlation of shadowing among proximate wireless links has been frequently observed. Although different types of correlated shadowing models have been proposed for wireless channels, these models are not present in popular network simulators. Ignoring such correlations results in the diversity of adjacent links being over- estimated. Our hypothesis is that this could lead to incorrect results when evaluating the performance of wireless systems and network protocols. In this paper, the ns-3 simulation environment has been enhanced with a prototype correlated shadowing model developed in our previously published work. We study the end-to-end packet delivery ratio and delay in wireless sensor networks using both correlated and independent propagation models. Simulation results show that correlated and independent shadowing models produce significant differences in network performance. Moreover, we compare the complexity of different modeling options. It is shown that this correlated propagation model in ns-3 can improve simulation realism without inducing any considerable degradation of scalability.

Shadowing losses on proximate wireless links have been experimentally proven to be highly correlated in various scenarios. However, most of the existing works on the reliability modeling of Wireless Multi-Hop Networks (WMHNs) assume independent link shadowing. Neglecting shadowing correlations could lead to inaccurate network simulation results and unreliable wireless system design. In this paper, we present a more realistic reliability model of WMHN that incorporates correlated link shadowing. In particular, we use the correlated shadowing model that was developed in our previous work. This model enables the efficient generation of spatially correlated shadowing. It has been proved to agree well with the literature in terms of statistical properties. The proposed network model allows us to predict the reliability metrics of WMHNs and study network designs that can lessen the effect of correlated shadowing. Numerical results indicate that it is important to use the correlated shadowing model when evaluating the reliability of densely deployed large-scale multi-hop networks. We also present some numerical results to show the influence of shadowing correlation on redundant node deployment. This paper makes a small but fundamental step towards reliable wireless multi-hop network design in the context of correlated link shadowing.

Complexity is ever increasing within our information environment and organisations, as interdependent dynamic relationships within sociotechnical systems result in high variety and uncertainty from a lack of information or control. A net-centric approach is a strategy to improve information value, to enable stakeholders to extend their reach to additional data sources, share Situational Awareness (SA), synchronise effort and optimise resource use to deliver maximum (or proportionate) effect in support of goals. This paper takes a systems perspective to understand the dynamics within a net-centric information system. This paper presents the first stages of the Soft Systems Methodology (SSM), to develop a conceptual model of the human activity system and develop a system dynamics model to represent system behaviour, that will inform future research into a net-centric approach with information security. Our model supports the net-centric hypothesis that participation within a information sharing community extends information reach, improves organisation SA allowing proactive action to mitigate vulnerabilities and reduce overall risk within the community. The system dynamics model provides organisations with tools to better understand the value of a net-centric approach, a framework to determine their own maturity and evaluate strategic relationships with collaborative communities.

There is a gap in the ability to gain sufficient Situational Awareness (SA) of the cyber domain at the strategic level, leading nations and organisations to rapidly develop this capability. Through various cyber strategies, nations are seeking to encourage multi-organisation collaboration and information infrastructures between government, military, critical national infrastructure and engaging with the public and private sectors to secure cyberspace and its dependencies. This paper discusses the benefits of a systems approach to the complex sociotechnical problem of collaboration towards a cyber defence capability, and how challenges can be managed through the perspective of a viable system. The Viable Systems Model (VSM) provides a perspective for understanding system behaviour and anticipating, planning, and implementing large scale organisational change. The output from focus group sessions with stakeholders across national infrastructure, are placed in context to the VSM to provide a framework to better understand the challenges from the cyber domain, points of intervention, and requirements for a viable collaborative cyber defence system. Without a holistic, efficient information infrastructure supporting a cyber SA capability, the ability for a whole system response to take a proactive posture to threats or put in place effective mitigation and resilience measures is severely reduced, leading to even greater vulnerability. Relevance to industry This paper presents the outputs from a number of focus groups with stakeholders drawn from national infrastructure and business sectors, that are place within the context of the VSM. The VSM is presented as a framework to identify requirements and intervention points for future research towards a collaborative information system architecture.

Correlated shadow fading has a detrimental effect on the performance of wireless systems. Neglecting shadowing correlations could lead to inaccurate simulation results and unreliable wireless system design. In this paper, we propose and analyze a correlated shadow fading model based on Gaussian random fields. The model enables the generation of spatially correlated shadow fading for all meshed links in wireless multi-hop networks. Both analytical and numerical results show that the proposed model is in good agreement with the literature in terms of the statistical properties and correlation coefficients. Furthermore, the Circulant Embedding method of the proposed simulation model significantly reduces the computational cost.

PerfTrack is a data store and interface for managing performance data from large-scale parallel applications. Data collected in different locations and formats can be compared and viewed in a single performance analysis session. The underlying data store used in PerfTrack is implemented with a database management system (DBMS). PerfTrack includes interfaces to the data store and scripts for automatically collecting data describing each experiment, such as build and platform details. We have implemented a prototype of PerfTrack that can use Oracle or PostgreSQL for the data store. We demonstrate the prototype's functionality with three case studies: one is a comparative study of an ASC purple benchmark on high-end Linux and AIX platforms; the second is a parameter study conducted at Lawrence Livermore National Laboratory (LLNL) on two high end platforms, a 128 node cluster of IBM Power 4 processors and BlueGene/L; the third demonstrates incorporating performance data from the Paradyn Parallel Performance Tool into an existing PerfTrack data store.

Abstract Comparisons of high‐performance computers based on their peak floating point performance are common but seldom useful when comparing performance on real workloads. Factors that influence sustained performance extend beyond a system's floating‐point units, and real applications exercise machines in complex and diverse ways. Even when it is possible to compare systems based on their performance, other considerations affect which machine is best for a given organization. These include the cost, the facilities requirements (power, floorspace, etc.), the programming model, the existing code base, and so on. This paper describes some of the important measures for evaluating high‐performance computers. We present data for many of these metrics based on our experience at Lawrence Livermore National Laboratory (LLNL), and we compare them with published information on the Earth Simulator. We argue that evaluating systems involves far more than comparing benchmarks and acquisition costs. We show that evaluating systems often involves complex choices among a variety of factors that influence the value of a supercomputer to an organization, and that the high‐end computing community should view cost/performance comparisons of different architectures with skepticism. Published in 2005 by John Wiley & Sons, Ltd.