A Multi-User Ad-Hoc Resource Manager for Public Urban Areas

Smart spaces are defined as an environment capable of communicating with users in order to support them in achieving a goal. Previously, smart spaces were restricted to closed private areas in a well defined environment. However, factors such as the omnipresence of mobile devices, the advancement in wireless communication, and the low cost of technological infrastructure allows the creation of smart spaces everywhere. One trend that is acquiring relevance these days is to use surrounding public resources to perform tasks on behalf of mobile devices, which are resource constrained. To achieve this, systems should be able to control the access to public resources, minimize possible interference among users, and maintain the purpose of public resources untouched. This work presents a multi-user ad-hoc resource manager for smart urban areas based on previous considerations. The current system helps to avoid conflicts between users by means of a distributed scheme based on social gain for the community. The management is performed without the need of a central infrastructure. Results show that it is possible to discover and manage public resources from mobile devices while handling conflicts in a distributed manner.

Optimizing User Quality of Experience through Overlay Routing, Bandwidth Management and Dynamic Trans-Coding

Accessing multimedia services via fixed and wireless networks has become common practice. These services are typically much more sensitive to packet loss, delay and/or congestion than traditional services. In particular, multimedia data is often time critical and, as a result, network issues are not well tolerated and significantly deteriorate the user’s Quality of Experience (QoE). Therefore, the authors propose a QoE optimization platform that is able to mitigate problems that might occur at any location in the delivery path from service provider to customer. More specifically, the distributed architecture supports overlay routing to circumvent erratic parts of the network core. In addition, it comprises proxy components that realize last mile optimization through automatic bandwidth management and the application of processing on multimedia flows. This paper introduces a trans-coding service for this proxy component which enables the transformation of H.264/AVC video flows to an arbitrary bitrate. Through representative experimental results, the authors illustrate how this addition enhances the QoE optimization capabilities of the proposed platform by allowing the proxy component to compute more flexible and effective bandwidth distributions.

Adaptive Modeling of Routing Algorithms for Wireless Sensor Networks

Recent years have witnessed a proliferation of routing algorithms for Wireless Sensor Networks (WSNs), hence complicating the choice of the proper algorithm to be used for a given application. Simulation frameworks represent a viable solution to anticipate crucial choices, however existing solutions do not encompass the impact of changes (e.g., route updates, node crashes) on the nodes behavior and vice-versa. This article proposes a novel adaptive modeling approach to master the complexity of the thorough simulation of routing algorithms for WSN. Experimental results are provided showing the effectiveness of the proposed approach at managing changes, and dealing with detailed aspects, during the simulation and comparison of several routing algorithms.

A Multi-User Ad-Hoc Resource Manager for Public Urban Areas

Smart spaces are defined as an environment capable of communicating with users in order to support them in achieving a goal. Previously, smart spaces were restricted to closed private areas in a well defined environment. However, factors such as the omnipresence of mobile devices, the advancement in wireless communication, and the low cost of technological infrastructure allows the creation of smart spaces everywhere. One trend that is acquiring relevance these days is to use surrounding public resources to perform tasks on behalf of mobile devices, which are resource constrained. To achieve this, systems should be able to control the access to public resources, minimize possible interference among users, and maintain the purpose of public resources untouched. This work presents a multi-user ad-hoc resource manager for smart urban areas based on previous considerations. The current system helps to avoid conflicts between users by means of a distributed scheme based on social gain for the community. The management is performed without the need of a central infrastructure. Results show that it is possible to discover and manage public resources from mobile devices while handling conflicts in a distributed manner.

Towards Adaptive and Scalable Context Aware Middleware

The diffusion of portable client devices is promoting the spreading of novel mobile services, both traditional such as email and printing, and new such as social computing applications, capable of opportunistically exploiting any computing resource and any wireless connectivity encountered by roaming users. The new requirements call for novel context-aware middlewares to support and simplify the retrieval and the usage of context data. However, existing context data dissemination infrastructures still present several limitations: they are unable to adaptively exploit impromptu any wireless communication opportunity; they are unable to scale, especially in wide/densely populated environments; and they are prone to connection/device flaws. The article proposes a novel context-aware middleware that achieves adaptability, scalability, and dependability in context data dissemination through three main core guidelines: by using a distributed hierarchical architecture, by employing lightweight and adaptive context data dissemination solutions, and by adopting statistical context data/query replication techniques. The performance results, obtained by extensively testing the proposed solution in our wireless university campus testbed, have validated our design choices.

Resilient and Timely Event Dissemination in Publish/Subscribe Middleware

Recently we have witnessed an increasing demand of fault-tolerant communications in publish/subscribe middleware. Although several reliable solutions have been proposed, none of them address the problem of achieving a resilient and timely event dissemination. We investigate how guaranteeing assured message dissemination despite occurrence of network faults without breaking temporal constraints. The contribution of this article is on devising a FEC approach where encoding functionality is placed at the root and on a subset of interior nodes in the multicast tree. Simulations-based experiments demonstrate that the proposed approach allows all the interested subscribers to receive all the published messages and the adopted resiliency mean does not affect the performance of the multicast protocol.

Beernet

Distributed systems with a centralized architecture present the well known problems of single point of failure and single point of congestion; therefore, they do not scale. Decentralized systems, especially as peer-to-peer networks, are gaining popularity because they scale well, and do not need a server to work. However, their complexity is higher due to the lack of a single point of control and synchronization, and because consistent decentralized storage is difficult to maintain when data constantly evolves. Self-management is a way of handling this higher complexity. In this paper, the authors present a decentralized system built with a structured overlay network that is self-organized and self-healing, providing a transactional replicated storage for small or large scale systems.

Technological and Educational Challenges of Resilient Computing

The adjective resilient has been used in dependable computing essentially as a synonym of fault-tolerant, thus ignoring the unexpected aspect of the phenomena the systems may have to face. These phenomena are very relevant when moving to systems like the future large, networked, evolving systems constituting complex information infrastructures that are the emergence of the ubiquitous systems that will support Ambient Intelligence. From an educational point of view, very few Universities offer a comprehensive track that is able to prepare students able to cope with the challenges posed by the design of ubiquitous systems. To fill both gaps, a European Network of Excellence, ReSIST – Resilience for Survivability in IST, was run from January 2006 to March 2009 (see http://www.resist-noe.org/). In this article the technological challenges, the related educational issues and a proposed MSc curriculum in Resilient Computing that arise from the results of ReSIST are presented and discussed.

A Machine Learning Based Meta-Scheduler for Multi-Core Processors

Sharing resources such as caches and memory buses between the cores of multi-core processors may cause performance bottlenecks for running programs. In this paper, the authors describe a meta-scheduler, which adapts the process scheduling decisions for reducing the contention for shared L2 caches on multi-core processors. The meta-scheduler takes into account the multi-core topology as well as the L2 cache related characteristics of the processes. Using the model generated by the process of machine learning, it predicts the L2 cache behavior, i.e., solo-run-L2-cache-stress, of the programs. It runs in user mode and guides the underlying operating system process scheduler in intelligent scheduling of processes to reduce the contention of shared L2 caches. In these experiments, the authors observed up to 12 percent speedup in individual as well as overall performance, while using meta-scheduler as compared to default process scheduler (Completely Fair Scheduler) of Linux kernel.

Reliability-Aware Proactive Energy Management in Hard Real-Time Systems

Advanced technologies such as sub-45nm CMOS and 3D integration are known to have more accelerated and increased number of reliability failure mechanisms. Classical reliability assessment methodology, which assumes ad-hoc failure criteria and worst-case for all influencing dynamic aspects, is no longer viable in these technologies. In this paper, the authors advocate that managing temperature and reliability at run-time is necessary to overcome this reliability-wall without incurring significant cost penalty. Nonlinear nature of modern systems, however, makes the run-time control very challenging. The authors suggest that full cost-consciousness requires a truly proactive controller that can efficiently manage system slack with future in perspective. This paper introduces the concept of “gas-pedal,” which enhances the effectiveness of the proactive controller in minimizing the cost without sacrificing the hard guarantees required by the constraints. Reliability-aware dynamic energy management of a processor running AVC motion compensation task is used as a motivational case study to illustrate the proposed concepts.