A Self-Stabilizing K-Clustering Algorithm Using an Arbitrary Metric (Revised Version of RR2008-31)

32 pagesMobile ad hoc networks as well as grid platforms are distributed, changing, and error prone environments. Communication costs within such infrastructure can be improved, or at least bounded, by using k-clustering. A k-clustering of a graph, is a partition of the nodes into disjoint sets, called clusters, in which every node is distance at most k from a designated node in its cluster, called the clusterhead. A self-stabilizing asynchronous distributed algorithm is given for constructing a k-clustering of a connected network of processes with unique IDs and weighted edges. The algorithm is comparison-based, takes O(nk) time, and uses O(log n + log k) space per process, where n is the size of the network. This is the first distributed solution to the k-clustering problem on weighted graphs

Vers une structuration auto-stabilisante des réseaux Ad Hoc

International audienceIn this paper, we present a self-stabilizing asynchronous distributed clustering algorithm that builds non-overlapping k-hops clusters. Our approach does not require any initialization. It is based only on information from neighboring nodes with periodic messages exchange. Starting from an arbitrary configuration, the network converges to a stable state after a finite number of steps. Firstly, we prove that the stabilization is reached after at most n+2 transitions and requires (u+1)* log(2n+k+3) bits per node, whereΔu represents node's degree, n is the number of network nodes and k represents the maximum hops number. Secondly, using OMNet++ simulator, we performed an evaluation of our proposed algorithm.Dans cet article, nous proposons un algorithme de structuration auto-stabilisant, distribuéet asynchrone qui construit des clusters de diamètre au plus 2k. Notre approche ne nécessite aucuneinitialisation. Elle se fonde uniquement sur l’information provenant des noeuds voisins à l’aided’échanges de messages. Partant d’une configuration quelconque, le réseau converge vers un étatstable après un nombre fini d’étapes. Nous montrons par preuve formelle que pour un réseau de nnoeuds, la stabilisation est atteinte en au plus n + 2 transitions. De plus, l’algorithme nécessite uneoccupation mémoire de (u + 1) log(2n + k + 3) bits pour chaque noeud u où u représente ledegré (nombre de voisins) de u et k la distance maximale dans les clusters. Afin de consolider lesrésultats théoriques obtenus, nous avons effectué une campagne de simulation sous OMNeT++ pourévaluer la performance de notre solution

Enhancenig OLSR routing protocol using K-means clustering in MANETs

The design of robust routing protocol schemes for MANETs is quite complex, due to the characteristics and structural constraints of this network. A numerous variety of protocol schemes have been proposed in literature. Most of them are based on traditional method of routing, which doesn’t guarantee basic levels of Qos, when the network becomes larger, denser and dynamic. To solve this problem we use one of the most popular methods named clustering. In this work we try to improve the Qos in MANETs. We propose an algorithm of clustering based in the new mobility metric and K-Means method to distribute the nodes into several clusters; it is implemented to standard OLSR protocol giving birth a new protocol named OLSR Kmeans-SDE. The simulations showed that the results obtained by OLSR Kmeans-SDE exceed those obtained by standard OLSR Kmeans and OLSR Kmed+ in terms of, traffic Control, delay and packet delivery ratio

On the Performances of the Routing Protocols in MANET: : Classical versus Self-Organized Approaches

International audienceMobile Ad Hoc Networks (MANET) are spontaneous wireless networks of mobile nodes without any fixed infrastructure. MANET are promised to a large spectrum of military or civilian utilizations. Routing is a key topic in such networks: overhead must be minimized, optimizing the delay and reducing the packet losses. Several routing protocols were proposed in the literature but, recently, new routing protocols based on a self-organization, like Virtual Structure Routing (VSR), were proposed. VSR is based on a self-organized structure with an important stability and persistence. In this paper, we aim to quantify the contribution of the self-organization on the routing behavior and performances. We oppose VSR as a self-organized protocol to the classical one: reactive (AODV), proactive (OLSR) and clustered (CBRP). The impact of the mobility and the density, the horizontal and the vertical scalabilities are studied

Self-Evaluation Applied Mathematics 2003-2008 University of Twente

This report contains the self-study for the research assessment of the Department of Applied Mathematics (AM) of the Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) at the University of Twente (UT). The report provides the information for the Research Assessment Committee for Applied Mathematics, dealing with mathematical sciences at the three universities of technology in the Netherlands. It describes the state of affairs pertaining to the period 1 January 2003 to 31 December 2008

CLUSTER RANDOMIZED CONTROLLED TRIAL TO EVALUATE THE EFFECTIVENESS OF A MULTIFACETED ACTIVE STRATEGY TO IMPLEMENT LOW BACK PAIN PRACTICE GUIDELINES; EFFECT ON COMPETENCE, PROCESS OF CARE AND PATIENT OUTCOMES IN PHYSICAL THERAPY

The study was a cluster randomized controlled trial designed to evaluate the effectiveness of an active strategy to implement practice guidelines for low back pain in physical therapy. Physical therapy clinics (clinics=28, therapists=41) were randomized to receive a multifaceted active intervention (education, audit, feedback) (clinics=16, therapists=24) to increase awareness regarding key recommendations in guidelines or mailed guidelines (clinics=12, therapists=18). Primary outcome measures were change in pre to post intervention competence score (18 clinical vignettes), adherence to guidelines and change in patient Oswestry scores from first to last visit. The competence test was administered at baseline and on completion of the education course. Data on LBP patients treated by participating therapists in a 12-week pre (therapists=41, patients=50) and post (therapists=41, patients=107) intervention period (education, audit and feedback) was extracted from the UPMC electronic database. Patient care was classified as being adherent or non-adherent using 6 quality indicators developed to reflect recommendations in the guidelines. Overall percentage of adherence and adherence to individual criterion on the guidelines were also calculated. The results of the study indicated that education did not have an effect improving knowledge measured by change in total competence score. However, there were significant differences between groups on the ability to appropriately identify directional preference with movement testing, where the intervention group did better than the control. Adherence to guidelines and patient outcomes did not improve as a result of the active intervention strategy. The groups were not significantly different when comparing overall adherence to guidelines or to individual criterion on guidelines. There was an underutilization of mobilization thrust (82.3%), traction (78.5%) and graded exercises (47.6%) for fear avoidant patients, while stabilization was over-utilized in 51% of patients. Although therapists demonstrated moderate to high scores on the competence test, they failed to apply this knowledge in clinical practice. Future research should focus on a qualitative inquiry into organizational and environmental barriers to adoption of clinical practice guidelines. These include evaluating if payment policies and reimbursement from providers are aligned with guidelines and also assessing the extent to which patient demands and compliance influences adherence to guidelines

Compositional gossip: a conceptual architecture for designing gossip-based applications

Most proposed gossip-based systems use an ad-hoc design. We observe a low degree of reutilization among this proposals. We present how this limits both the systematic development of gossip-based applications and the number of applications that can benefit from gossip-based construction. We posit that these reinvent-the-wheel approaches poses a significant barrier to the spread and usability of gossip protocols. This paper advocates a conceptual design framework based upon aggregating basic and predefined building blocks BD 2. We show how to compose building blocks within our framework to construct more complex blocks to be used in gossip-based applications. The concept is further depicted with two gossip-based applications described using our building blocks.(undefined

EEG Characterization of Sensorimotor Networks: Implications in Stroke

The purpose of this dissertation was to use electroencephalography (EEG) to characterize sensorimotor networks and examine the effects of stroke on sensorimotor networks. Sensorimotor networks play an essential role in completion of everyday tasks, and when damaged, as in stroke survivors, the successful completion of seemingly simple motor tasks becomes fantasy. When sensorimotor networks are impaired as a result of stroke, varying degrees of sensorimotor deficits emerge, most often including loss of sensation and difficulty generating upper extremity movements. Although sensory therapies, such as the application of tendon vibration, have been shown to reduce the sensorimotor deficits after stroke, the underlying sensorimotor mechanisms associated with such improvements are unknown. While sensorimotor networks have been studied extensively, unanswered questions still surround their role in basic control paradigms and how their role changes after stroke. EEG provides a way to probe the high-speed temporal dynamics of sensorimotor networks that other more common imaging modalities lack. Sensorimotor network function was examined in controls during a task designed to differentiate potential mechanisms of arm stabilization and determine to what degree the sensorimotor network is involved. After sensorimotor network function was characterized in controls, we examined the effect of stroke on the sensorimotor network during rest and described the reorganization that occurs. Lastly, we explored tendon vibration as a sensory therapy for stroke survivors and determined if sensorimotor network mechanisms underlie improvements in arm tracking performance due to wrist tendon vibration. We observed cortical activity and connectivity that suggests sensorimotor networks are involved in the control of arm stability, cortical networks reorganize to more asymmetric, local networks after stroke, and tendon vibration normalizes sensorimotor network activity and connectivity during motor control after stroke. This dissertation was among the first studies using EEG to characterize the high-speed temporal dynamics of sensorimotor networks following stroke. This new knowledge has led to a better understanding of how sensorimotor networks function under ordinary circumstances as well as extreme situations such as stroke and revealed previously unknown mechanisms by which tendon vibration improves motor control in stroke survivors, which will lead to better therapeutic approaches

An Emergent Architecture for Scaling Decentralized Communication Systems (DCS)

With recent technological advancements now accelerating the mobile and wireless Internet solution space, a ubiquitous computing Internet is well within the research and industrial community's design reach - a decentralized system design, which is not solely driven by static physical models and sound engineering principals, but more dynamically, perhaps sub-optimally at initial deployment and socially-influenced in its evolution. To complement today's Internet system, this thesis proposes a Decentralized Communication System (DCS) architecture with the following characteristics: flat physical topologies with numerous compute oriented and communication intensive nodes in the network with many of these nodes operating in multiple functional roles; self-organizing virtual structures formed through alternative mobility scenarios and capable of serving ad hoc networking formations; emergent operations and control with limited dependency on centralized control and management administration. Today, decentralized systems are not commercially scalable or viable for broad adoption in the same way we have to come to rely on the Internet or telephony systems. The premise in this thesis is that DCS can reach high levels of resilience, usefulness, scale that the industry has come to experience with traditional centralized systems by exploiting the following properties: (i.) network density and topological diversity; (ii.) self-organization and emergent attributes; (iii.) cooperative and dynamic infrastructure; and (iv.) node role diversity. This thesis delivers key contributions towards advancing the current state of the art in decentralized systems. First, we present the vision and a conceptual framework for DCS. Second, the thesis demonstrates that such a framework and concept architecture is feasible by prototyping a DCS platform that exhibits the above properties or minimally, demonstrates that these properties are feasible through prototyped network services. Third, this work expands on an alternative approach to network clustering using hierarchical virtual clusters (HVC) to facilitate self-organizing network structures. With increasing network complexity, decentralized systems can generally lead to unreliable and irregular service quality, especially given unpredictable node mobility and traffic dynamics. The HVC framework is an architectural strategy to address organizational disorder associated with traditional decentralized systems. The proposed HVC architecture along with the associated promotional methodology organizes distributed control and management services by leveraging alternative organizational models (e.g., peer-to-peer (P2P), centralized or tiered) in hierarchical and virtual fashion. Through simulation and analytical modeling, we demonstrate HVC efficiencies in DCS structural scalability and resilience by comparing static and dynamic HVC node configurations against traditional physical configurations based on P2P, centralized or tiered structures. Next, an emergent management architecture for DCS exploiting HVC for self-organization, introduces emergence as an operational approach to scaling DCS services for state management and policy control. In this thesis, emergence scales in hierarchical fashion using virtual clustering to create multiple tiers of local and global separation for aggregation, distribution and network control. Emergence is an architectural objective, which HVC introduces into the proposed self-management design for scaling and stability purposes. Since HVC expands the clustering model hierarchically and virtually, a clusterhead (CH) node, positioned as a proxy for a specific cluster or grouped DCS nodes, can also operate in a micro-capacity as a peer member of an organized cluster in a higher tier. As the HVC promotional process continues through the hierarchy, each tier of the hierarchy exhibits emergent behavior. With HVC as the self-organizing structural framework, a multi-tiered, emergent architecture enables the decentralized management strategy to improve scaling objectives that traditionally challenge decentralized systems. The HVC organizational concept and the emergence properties align with and the view of the human brain's neocortex layering structure of sensory storage, prediction and intelligence. It is the position in this thesis, that for DCS to scale and maintain broad stability, network control and management must strive towards an emergent or natural approach. While today's models for network control and management have proven to lack scalability and responsiveness based on pure centralized models, it is unlikely that singular organizational models can withstand the operational complexities associated with DCS. In this work, we integrate emergence and learning-based methods in a cooperative computing manner towards realizing DCS self-management. However, unlike many existing work in these areas which break down with increased network complexity and dynamics, the proposed HVC framework is utilized to offset these issues through effective separation, aggregation and asynchronous processing of both distributed state and policy. Using modeling techniques, we demonstrate that such architecture is feasible and can improve the operational robustness of DCS. The modeling emphasis focuses on demonstrating the operational advantages of an HVC-based organizational strategy for emergent management services (i.e., reachability, availability or performance). By integrating the two approaches, the DCS architecture forms a scalable system to address the challenges associated with traditional decentralized systems. The hypothesis is that the emergent management system architecture will improve the operational scaling properties of DCS-based applications and services. Additionally, we demonstrate structural flexibility of HVC as an underlying service infrastructure to build and deploy DCS applications and layered services. The modeling results demonstrate that an HVC-based emergent management and control system operationally outperforms traditional structural organizational models. In summary, this thesis brings together the above contributions towards delivering a scalable, decentralized system for Internet mobile computing and communications