George Kormentzas

The IEEE 802.11g standard for high data rate WLANs

Continuous WLAN public acceptance comes with increasing demand for provision of higher data rates. Building on this context, the IEEE published the IEEE 802.11g standard for providing data rates of up to 54 Mb/s at the 2.4 GHz band. This article presents the new features of IEEE 802.11g and, using an open source C++-based simulation tool, evaluates both the performance and effectiveness of these features compared to the older IEEE 802.11 standard versions.

On the building blocks of quality of service in heterogeneous IP networks

After more than a decade of active research on Quality of Service in IP networks and the Internet, the majority of IP traffic relies on the conventional best-effort IP service model. Nevertheless, some QoS mechanisms are deployed in current networking infrastructures, while emerging applications pose QoS challenges. This survey brings into the foreground a broad range of research results on Quality of Service in IP-based networks. First, a justification of the need for QoS is provided, along with challenges stemming from the convergence of IP and wireless networks and the proliferation of QoS-demanding IP applications (such as VoIP). It is also emphasized that a global uniform end-to-end IP QoS solution is not realistic. Based on this remark, packet-level QoS mechanisms are classified as certain building blocks, each one fulfilling different objectives in certain parts of a heterogeneous IP network. This taxonomy, being in line with the ITU-T initiative toward a QoS architectural framework for IP networks, gives rise to a thorough presentation of QoS “building blocks,” as well as their associated mechanisms. This presentation is followed by an illustration of how the various building blocks are combined in the scope of modern IP networks. However, offering QoS in a large scale IP-based network demands that additional (i.e. non-packet-level) QoS mechanisms are deployed in some parts. Therefore, we also present prominent technologies and mechanisms devised to augment the QoS capabilities of access, wireless, and optical networks. We illustrate how these mechanisms boost end-to-end QoS solutions and reveal interworking issues with packet-level mechanisms.

Wavelet-Based Compression With ROI Coding Support for Mobile Access to DICOM Images Over Heterogeneous Radio Networks

Most of the commercial medical image viewers do not provide scalability in image compression and/or region of interest (ROI) encoding/decoding. Furthermore, these viewers do not take into consideration the special requirements and needs of a heterogeneous radio setting that is constituted by different access technologies [e.g., general packet radio services (GPRS)/ universal mobile telecommunications system (UMTS), wireless local area network (WLAN), and digital video broadcasting (DVB-H)]. This paper discusses a medical application that contains a viewer for digital imaging and communications in medicine (DICOM) images as a core module. The proposed application enables scalable wavelet-based compression, retrieval, and decompression of DICOM medical images and also supports ROI coding/decoding. Furthermore, the presented application is appropriate for use by mobile devices activating in heterogeneous radio settings. In this context, performance issues regarding the usage of the proposed application in the case of a prototype heterogeneous system setup are also discussed.

Delay Performance Analysis and Evaluation of IEEE 802.11e EDCA in Finite Load Conditions

The paper presents an analytical model for the performance evaluation of IEEE 802.11e EDCA scheme under finite load conditions on the basis of various instances of delay metric (i.e., media access delay, queuing delay and total delay). The simulation results show that the analytical estimated instances of the delay metric are almost accurate. The paper exhibits that concerning the delay of serving classes, EDCA compared to the conventional DCF, favors high priority classes against low priority ones, while almost does not affect the behavior of medium ones.

Intelligent one-stop-shop travel recommendations using an adaptive neural network and clustering of history.

The rapid growth of e-commerce during the last years has obliged a significant number of companies and professionals from diverse fields to turn to the Internet as a medium through which they aim to promote their products and services. A main issue for product and service providers is that, as this new market is characterized by the lack of personal contact, it is difficult to offer personalized services to end users; it is this type of service that end users look for and remain faithful to. Recommender systems belong to a new breed of software that aims to fill this gap; they rely on the analysis of past user actions to estimate the optimal way with which to interact with each user. In this article we explain why existing recommender systems are not adequate to provide for efficient personalization of interaction in the area of travel services, as they cannot support the user in all the phases of travel planning, and propose a new scheme to overcome the identified difficulties. Our approach considers the relation between different types of services in the usage history of the system. It is based on a hierarchical clustering of usage history to extract meaningful usage patterns, as well as an adaptive neural network structure that allows for online adaptation to the user, and enables the offering of intelligent recommendations.

Service-driven inter-domain QoS monitoring system for large-scale IP and DVB networks

There is a growing synergy between well-established Service Providers (SP), Content Providers (CP), and Network Providers (NP), to propose new value-added services, and hence opening new markets to generate further revenues. Meanwhile, the explosive increasing amount of multimedia content to be offered in the Internet and the heterogeneity of the underlying networking technologies demand the provision of new QoS-enabled mechanisms and architecture to efficiently control, manage and monitor the networks. Quality of service monitoring is becoming crucial to SPs for providing quantified QoS-based services and service assurance and to NPs for managing network resources. This paper proposes a framework for large scale inter-domain QoS monitoring in heterogeneous networks including IP and DVB networks that has been developed in the IST-ENTHRONE project of European Commission. One of the main aims is actually to allow high cooperation between different providers while keeping intact the authority, confidentiality, and full control of each provider over its underlying resources. The proposed monitoring framework consists of a layered architecture with two signaling protocols namely an inter-domain monitoring signaling protocol (EQoS-RM), and an intra-domain active measurement signaling protocol (Emon). The proposed QoS monitoring system is service-driven in the sense that it aimed at providing in service verification of QoS performance guarantees for the services offered to the users by the providers. To achieve this, it uses both QoS probes that perform both active and passive monitoring at different levels of abstraction employing node and network wide measurements and application-level perceived quality meters for detecting quality degradation. As such, this framework specifies three types of QoS monitoring components operating at different levels: at network element or node, at network and at service levels. This proposed system also provides monitoring information to NPs in order to assist in managing the operational status of their networks. Design and implementation of the proposed QoS monitoring system is described in this paper. Some experimental assessments of this service-driven QoS monitoring system prove its functioning in terms of accuracy and responsiveness in providing the necessary results.

Seamless service provision for multi heterogeneous access

The key enabling function for seamless mobility and service continuity among a variety of wireless access technologies is the handover. Handovers within the same radio system are addressed by the standardization bodies involved in the development of the corresponding technologies (e.g., 3GPP, 3GPP2, IEEE, DVB), while handovers between heterogeneous systems are managed by protocols developed by the IETF. However, the interoperability between radio access systems that is required to realize the vision of Beyond 3G calls for coordinated actions and integrated solutions combining individual strengths. This article reviews emerging protocols and architectures aiming to support intersystem handovers between nextgeneration wireless systems and presents an optimized handover framework built around the functionality introduced by the IEEE 802.21 standard. Mapping of this framework to the entities of the 3GPP evolved system architecture is discussed and handover procedures involving key entities of this architecture are presented.

Converged wireless networking and optimization for next generation services

The Next Generation Network (NGN) vision is tending towards the convergence of internet and mobile services providing the impetus for new market opportunities in combining the appealing services of internet with the roaming capability of mobile networks. However, this convergence does not go far enough, and with the emergence of new coexistence scenarios, there is a clear need to evolve the current architecture to provide cost-effective end-to-end communication. The LOOP project, a EUREKA-CELTIC driven initiative, is one piece in the jigsaw by helping European industry to sustain a leading role in telecommunications and manufacturing of high-value products and machinery by delivering pioneering converged wireless networking solutions that can be successfully demonstrated. This paper provides an overview of the LOOP project and the key achievements that have been tunneled into first prototypes for showcasing next generation services for operators and process manufacturers.

A Fusion IP/DVB Networking Environment for Providing Always-On Connectivity and Triple-Play Services to Urban and Rural Areas

This article introduces and validates a concept for the realization of a fusion IP/DVB networking environment that supports the provision of urban and rural always-on connectivity and triple-play services. Specifically, the proposed fusion environment realizes a unified infrastructure that changes traditional, passive urban users into active, information society participants capable of creating, manipulating, and distributing their own content/services over a commonly exploited infrastructure. Further, the environment enables triple-play services and always-on connectivity in rural areas, that is, in regions where there is no termination of the core backbone to the local PSTN/ISDN exchanger. Finally, the article describes important directions for future research to follow to exploit the proposed IP/DVB unified platform for the synergy of emerging broadcasting, telecommunications, wireless, and wired technologies, to alleviate the digital divide that currently exists not only among countries but also within most countries

A centralised broker-based CR network architecture for TVWS exploitation under the RTSSM policy

The paper discusses the TV white spaces exploitation by a prototype centralised cognitive radio network architecture, under the real time secondary spectrum management scheme. Vital part of this architecture is a spectrum broker that coordinates the radio resources allocation process among secondary systems, as well as the transactions of spectrum trading following a fixed-price policy. Efficient broker operation as a matter of maximum-possible spectrum utilisation and minimum fragmentation is obtained by decision-making methods based on Backtracking, Simulated Annealing and Genetic algorithm. The validity of the proposed approach is verified via a number of experiments under controlled conditions, while its performance is evaluated against a number of secondary systems competing for TVWS exploitation, each one featuring different transmission characteristics.