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In this paper we consider the frameworks of Process Algebra and I/O Automata and we apply both towards the verification of a distributed leader-election protocol. Based on the two experiences we evaluate the approaches and draw initial conclusions with respect to their relative capabilities, strengths and usability. To the best of our knowledge, this is the first hands-on evaluation of the two models, and we view it as the cornerstone for a wider investigation of the strengths and weaknesses of the two methodologies in specifying and verifying (distributed) protocols. © 2008 IEEE. 195 204 Sponsors: IEEE Comput. Soc. Technical Committee on Distributed Processing Akamai Technologies, Inc. International Research Institute on Autonomic Network Computing Conference code: 73523 Cited By :5

In this paper we present FailRank, a novel framework for integrating and ranking information sources that characterize failures in a grid system. After the failing sites have been ranked, these can be eliminated from the job scheduling resource pool yielding in that way a more predictable, dependable and adaptive infrastructure. We also present the tools we developed towards evaluating the FailRank framework. In particular, we present the FailBase Repository which is a 38GB corpus of state information that characterizes the EGEE Grid for one month in 2007. Such a corpus paves the way for the community to systematically uncover new, previously unknown patterns and rules between the multitudes of parameters that can contribute to failures in a Grid environment. Additionally, we present an experimental evaluation study of the FailRank system over 30 days which shows that our framework identifies failures in 93% of the cases. We believe that our work constitutes another important step towards realizing adaptive Grid computing systems. © 2008 IEEE. 291 298 Conference code: 73523 Cited By :2

A new location-based reactive multi-hop protocol, namely the e-GPSR algorithm, is tested for the use in UWB sensor networks for logistic applications. Specifically, the impact of location information errors on the algorithmpsilas performance is investigated when a Manhattan mobility model is assumed and a suitable position prediction model is introduced. The performance improvement produced by the combination of the e-GPSR algorithm with the prediction model is measured in terms of increased success delivery rate and reduced failures obtained by means of extensive system simulations.

Wireless mesh networks (WMNs) based on the IEEE802.11 standards can be used as convenient replacements of wireline networks in the context of home networking to provide users with a variety of services inside the home context for their low cost and easiness of deployment. However, in order to effectively support multimedia as well as ordinary traffic through a WMN infrastructure, traffic control is generally needed as wireless communications, especially in mesh network configurations, can be affected by significant congestion and channel impairments problems. In this work we are focusing on performance assessment and enhancement in IEEE802.11 WMNs. Experimental results are presented using simulation models of IEEE802.11b technology obtained through the open source INET framework of OMNET++ simulator.

Date of Conference: 17-19 March 2008 Conference name: 9th International Symposium on Quality Electronic Design, ISQED 2008 Executing array based applications on a chip multiprocessor requires effective loop parallelization techniques. One of the critical issues that need to be tackled by an optimizing compiler in this context is loop scheduling, which distributes the iterations of a loop to be executed in parallel across the available processors. Most of the existing work in this area targets cache based execution platforms. In comparison, this paper proposes the first dynamic loop scheduler, to our knowledge, that targets scratch-pad memory (SPM) based chip multiprocessors, and presents an experimental evaluation of it. The main idea behind our approach is to identify the set of loop iterations that access the SPM and those that do not. This information is exploited at runtime to balance the loads of the processors involved in executing the loop nest at hand. Therefore, the proposed dynamic scheduler takes advantage of the SPM in performing the loop iteration-to-processor mapping. Our experimental evaluation with eight array/loop intensive applications reveals that the proposed scheduler is very effective in practice and brings between 13.7% and 41.7% performance savings over a static loop scheduling scheme, which is also tested in our experiments. © 2008 IEEE.

In this work, using a game-theoretic approach, cost-sensitive mechanisms that lead to reliable Internet-based computing are designed. In particular, we consider Internet-based master-worker computations, where a master processor assigns, across the Internet, a computational task to a set of potentially untrusted worker processors and collects their responses. Several game-theoretic models that capture the nature of the problem are analyzed and mechanisms that, for each given set of cost and system parameters, achieve high reliability are designed. Additionally, two specific realistic system scenarios are studied. These scenarios are a system of volunteering computing like SETI, and a company that buys computing cycles from Internet computers and sells them to its customers in the form of a task-computation service. Notably, under certain conditions, non redundant allocation yields the best trade-off between cost and reliability. © 2008 IEEE. 315 324 Sponsors: IEEE Comput. Soc. Technical Committee on Distributed Processing Akamai Technologies, Inc. International Research Institute on Autonomic Network Computing Conference code: 73523 Cited By :11

Date of Conference: 1-3 April 2008 Conference name: 6th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks and Workshops, 2008 This paper aims at comparing through simulations the network lifetime of a wireless sensor network using Bluetooth-enabled or IEEE802.15.4 compliant devices. The evaluation is performed under a common reference framework, namely the EMORANS scenario for wireless sensor networks. Since the two enabling technologies rely on different MAC paradigms, suitable definition of the performance metrics is needed, in order to make the comparison meaningful. Thus, the paper has also a methodological objective. In particular, three different definitions of network lifetime are introduced, and a comparison of performance obtained by applying the different definitions is provided. Then, the comparison between the two standards is introduced: it is shown that there are no orders of magnitude of difference in network lifetime when the two technologies are used and the choice of the technology depends on the application requirements.

Models and specifications can be used in the design of distributed applications to formally reason about their safety properties. However, the benefits of using formal methods are often negated by the ad hoc process of mapping the semantics of an abstract specification to algorithms designed to be executed on target distributed platforms. The challenge of formally specifying communication channels and correctly implementing them as algorithms that use realistic distributed system services is the focus of this paper. This work provides an original formal specification of an abstract asynchronous communication channel with support for dynamic creation and tear down of links between participating network nodes, and its implementation as an algorithm using Java sockets. The specification and the algorithm are expressed using the Input/Output Automata formalism, and it is proved that the algorithm correctly implements the specification, viz. that any externally observable behavior (trace) of the algorithm has a corresponding behavior of the specification. The approach presented here can be used to implement algorithms for dynamic systems, where communicating nodes may join, leave, and experience delays. The result is also of direct benefit to automated code generation, such as that implemented within the Input/Output Automata Toolkit at MIT. © 2008 IEEE. 211 219 Sponsors: IEEE Comput. Soc. Technical Committee on Distributed Processing Akamai Technologies, Inc. International Research Institute on Autonomic Network Computing Conference code: 73523 Cited By :2

Date of Conference: 7-9 Nov. 2007 Conference name: 22nd international symposium on computer and information sciences, 2007 Today, consumer electronic devices and PCs are inevitable parts of our daily life. Controlling those devices remotely is an important aspect of the technology. We have already universal remote control devices for controlling consumer electronic devices. Similarly, we may control our desktop and laptop PCs and their applications remotely via portable and smaller computers like PDAs and Pocket PCs. This paper presents a system and its architecture that enable a wireless-enabled PDA to control a PC and its applications remotely over a 802.11 or Bluetooth link. With such a system running on a PDA, a user can start, run and control PC applications from any location that is reachable via 802.11 link. This enables flexibility, ease of use, and freedom for the user of PC applications. ©2007 IEEE.

Date of Conference: 7-9 November 2007 Conference Name: 22nd International Symposium on Computer and Information Sciences, IEEE 2007 We present the solution of large-scale scattering problems involving three-dimensional closed conducting objects with arbitrary shapes. With an efficient parallelization of the multilevel fast multipole algorithm on relatively inexpensive computational platforms using distributed-memory architectures, we perform the iterative solution of integral-equation formulations that are discretized with tens of millions of unknowns. In addition to canonical problems, we also present the solution of real-life problems involving complicated targets with large dimensions.

Date of Conference: 7-9 Nov. 2007 Conference name: 22nd international symposium on computer and information sciences, 2007 Learning logical relations from examples expressed as first order facts has been studied extensively by the Inductive Logic Programming research. Learning with positive-only data may cause over generalization of examples leading to inconsistent resulting hypotheses. A learning heuristic inferring specific generalization of strings based on unique match sequences is shown to be capable of learning predicates with string arguments. This paper describes an inductive learner based on the idea of specific generalization of strings, and the given clauses are generalized by considering the background knowledge. ©2007 IEEE.

Date of Conference: 7-9 Nov. 2007 Conference name: 22nd international symposium on computer and information sciences, 2007 Keyphrases provide semantic metadata to summarize and characterize documents. Unfortunately, there are many digital documents especially on the Internet that do not have a list of assigned keyphrases. Assigning keyphrases to these documents manually is a tedious process and requires knowledge of the subject. Automatic Keyphrase Extraction solves this problem. In this paper, we present implementation of Keyphrase Extraction Algorithm (KEA) for Turkish as well as extending it with new features to improve its performance. ©2007 IEEE.

Date of Conference: 7-9 Nov. 2007 Conference name: 22nd international symposium on computer and information sciences, 2007 Threshold Broadcast Encryption (TBE) is a promising extension of threshold cryptography with its advantages over traditional threshold cryptosystems, such as eliminating the need of a trusted party, the ability of setting up the system by individual users independently and the ability of choosing the threshold parameter and the group of privileged receivers at the time of encryption. An ElGamal-based solution for TBE was proposed by Ghodosi et al. In this paper, we propose an improved ElGamal-based TBE scheme with reduced transmission cost. ©2007 IEEE.

Date of Conference: 7-9 Nov. 2007 Conference name: 22nd international symposium on computer and information sciences, 2007 Data management in Peer-to-Peer (P2P) systems is a complicated and challenging issue due to the scale of the network and highly transient population of peers. In this paper, we identify important research problems in P2P data management, and describe briefly some methods that have appeared in the literature addressing those problems. We also discuss some open research issues and directions regarding data management in P2P systems. ©2007 IEEE.

Date of Conference: 7-9 Nov. 2007 Conference name: 22nd international symposium on computer and information sciences, 2007 We propose novel parallel preconditioning schemes for the iterative solution of integral equation methods. In particular, we try to improve convergence rate of the ill-conditioned linear systems formulated by the electric-field integral equation, which is the only integral-equation formulation for targets having open surfaces. For moderate-size problems, iterative solution of the near-field system enables much faster convergence compared to the widely used sparse approximate inverse preconditioner. For larger systems, we propose an approximation strategy to the multilevel fast multipole algorithm (MLFMA) to be used as a preconditioner. Our numerical experiments reveal that this scheme significantly outperforms other preconditioners. With the combined effort of effective preconditioners and an efficiently parallelized MLFMA, we are able to solve targets with tens of millions of unknowns, which are the largest problems ever reported in computational electromagnetics. ©2007 IEEE.

Date of Conference: 1-4 July 2007 Conference name: 12th IEEE Symposium on Computers and Communications, 2007 UMTS is designed to offer high bandwidth radio access with QoS assurances for multimedia communications. In particular, real-time video communications services are expected to become a successful experience under UMTS networks. In this context, a video transmission service can be designed over the basis that UMTS can provide either a constant bit rate data channel or a dynamic variable bit rate data channel adapted to load conditions. In this latter approach, which is more efficient for both the user and the service provider, multimedia sources have to be timely designed in order to adapt their output rate to the instantaneous allowed channel rate. The target of this paper is to define an analytical model of adaptive real-time video sources in a UMTS network where system resources are dynamically shared among active users. © 2007 IEEE.

The high-level-architecture (HLA) is an IEEE standard for the interoperability and integration of (autonomous) simulation packages and applications (termed federates in the HLA context). It is based on a middleware-level component referred to as run-time-infrastructure (RTI) offering a set of interoperability services to the overlying simulation software. Time-management is the suite of services allowing synchronized execution among the federates, which, according to the HLA specification, covers pure conservative and pure optimistic synchronization schemes. In this paper we provide the design and implementation of a software layer, we refer to as risk-free-speculator (RFS), which supports an optimistic oriented intermediate approach to synchronization embedding the aggressiveness property of optimistic systems, but discarding risk. This is done in a totally transparent manner to the overlying applications, and does not even require any modification of the underlying RTI. The effectiveness of RFS has been tested against simulated demonstration exercises using the Joint Semi-Automated Forces (JSAF) simulation program.

This research has been funded by the The Scientific & Technological Research Council of Turkey (TUB ITAK), Project No: 104E130 and also supported in part by the Research Fund of the University of Istanbul. Project number: 513/05052006. In multi-sensor applications management of sensors is necessary for the classification of data they produce and for the efficient use of sensors as well. One of the important aspects in sensor management is the sensor scheduling. By scheduling the sensors, serious reductions can be achieved in the cost of bandwidth, power, and computation. In this work a simple solution for the problem of sensor scheduling in a multi-sensor target tracking application is presented. Due to non-linearity of the problem itself, proposed solution is presented in the framework of non-linear Bayesian estimation. Türkiye Bilimsel ve Teknolojik Araştırma Kurumu (TÜBİTAK) Istanbul University Publisher's Version WOS:000252265104001

International audience; In the robotic soccer domain, many factors, such as the speed of individual robots, the effectiveness of kicks, and the choice of the appropriate attacking strategy, determine the success of a team. Consequently , soccer robots, and in particular legged ones, require fine tuning of the parameters not only for the vision processes, but also in the implementation of behaviors and basic control actions and in the strategic decisional processes. In recent years, machine learning techniques have been used to find optimal parameter sets for different behaviors. In particular, layered learning has been proposed to improve learning rate in robot learning tasks. In this paper we consider a layered learning approach for learning optimal parameters of basic control routines, behaviours and strategy selection. We compare three different methods in the different layers: genetic algorithm, Nelder-Mead, and policy gradient. Moreover, we study how to use a 3D simulator for speeding up robot learning. The results of our experimental work on AIBO robots are useful not only to state differences and similarities between different robot learning approaches used within the layered learning framework, but also to evaluate a more effective learning methodology that makes use of a simulator.

It is beyond any doubt that the unpredictable nature of the today's Internet has tremendous impact on the transmission of video streams. With respect to the real-time nature of video streaming, unpredictable band-width, end-to-end delay and packet loss, are all problems that can affect video streaming over the Internet. The problem is worsened when we consider wireless and mobile users. In this paper we adopt Network Adaptation Techniques applied together with Content Adaptation Techniques to achieve graceful performance degradation as network load increases. We present a novel feedback mechanism and a fuzzy oriented decision algorithm which collectively provide video adaptation to network parameters. Our preliminary performance evaluations indicate that the fuzzy-based algorithm can finely sense the available bandwidth of the network path and adapt the video transmission rate accordingly, maintaining acceptable video quality. © 2007 IEEE. 219 226 Sponsors: IEEE Communications Society IEEE Computer Society Instituto de Telecomunicacoes Universidade de Aveiro Inovacao Conference code: 72823 Cited By :9

This paper investigates and proposes the introduction of a Supervisory and Notification Aggregator (SNA) service enabler in a Fixed Mobile Convergent (FMC) architecture. The SNA service enabler facilitates the deployment of advanced convergent services based on event notifications according to existing standards. The main functions and the components of the SNA service enabler are presented, while two examples of services that can be developed are analyzed illustrating the role of the SNA service enabler within a FMC architecture. © 2007 IEEE. 737 741

Detect and avoid procedures (DAA) are helpful to solve coexistence issues between ultra-wideband (UWB) devices and existing narrowband system operating in the same area and at the same time. We consider a system scenario where a narrowband UMTS terminal is considered to be primary and UWB devices create a secondary network on a local area basis. DAA procedures are only implemented in the UWB devices that coordinate their transmissions in order to reduce and/or to avoid interference to primary device(s) in the same area. UWB cannot alter the operations of the primary device in any way. We present and analyze the performance of an effective DAA procedure to be implemented in the UWB device(s) whose parameters can be tuned in order to reduce the percentage of time the UWB interferes the UMTS device. It is shown that interference reduction is obtained at the expense of a reduced performance of the UWB devices.

In this paper, a novel hybrid connection admission control (CAC) scheme combining downlink transmission power and aggregate throughput in the case of dedicated and shared connection setup respectively, is presented ("DPTCAC: downlink power/throughput based CAC algorithm"). The algorithm has special applicability in the case of wireless networks with particular emphasis on 3G UMTS networks (H. Kaaramen et al., 2001) enhanced with new multicasting technologies namely in this case "multimedia broadcast-multicast service (MBMS)". The motivation for introducing this hybrid CAC approach is twofold: the need to use a representative resource metric on which to base CAC decisions and the necessity to take advantage of the particularities of the resource allocation procedure in true multicast environments with connection sharing. We first present the algorithm which is based on previously conducted work in E.S. Elayoubi and T. Chahed (2004, 2005) augment this presentation with description of the hybrid nature of our proposal. We then compare via simulations the performance of the proposed algorithm against a reference "throughput based CAC algorithm (TCAC)" (H. Holma and A. Toskala, 2001). Simulation results show a beneficial effect of DPTCAC's applicability on cell capacity without observable degradation of offered QoS

OFDMA/OFDM multiple access/multiplexing techniques represent the radio interface technologies for the 4-th generation broadband cellular access networks such as the WiMAX operating the point-to-multipoint configuration. In this paper we consider the problem of the frequency reuse in cellular OFDMA/OFDM systems and in particular we calculate the reuse distance which is required to obtain a given link outage probability level. Analysis is carried out using a semi-analytical approach based on a general expression of the SINR accounting for multipath, frequency and time offsets between the reference terminal and the interfering devices. The proposed approach can be easily applied to evaluate performance under different operating modes of the OFDMA/OFDM cellular network e.g. synchronous BSs or not.

It is shown that Enhanced UMTS will be an affordable solution for providing the required network quality and to reduce infrastructure investments in offices scenarios. System capacity results are obtained by using a system level simulator which considers traffic characterisation parameters and services usage in detail, among other. Results for the most profitable cell radius are obtained via an optimisation procedure based in economic aspects. A higher number of pico cells (with a smaller radius, around 30-32 m) can be installed in the future, when costs of deploying and maintaining the network decreases, allowing for supporting higher system capacity, and reducing prices. Our approach is based in a detailed services analysis, which represents a worst case situation relatively to the total services approach, because the later does not discriminate results for the different traffic classes. The impact of call blocking, handover failure, end-to-end delay, and delay variation are taken into account. © 2006 IEEE. Conference code: 72218 Cited By :2

The 4-th generation broadband wireless interfaces for radio access will be based on OFDMA/OFDM multiple access/multiplexing techniques. The WiMAX operating the point- to-multipoint configuration is an important example. In this paper we consider some planning issues related to the problem of the frequency reuse in cellular-like OFDMA/OFDM systems. We obtain a general expression of the SINR at the receiver (base station or terminal) accounting for multipath, frequency and time offsets between the reference receiver and the interfering devices. The proposed approach can be easily applied to evaluate performance under different operating modes of the OFDMA/OFDM cellular network e.g. synchronous BSs or not.