This paper presents a reinforcement learningbased approach for optimizing the performance of $\mathbf{5 G}$ mobile networks. By leveraging Deep Q-Networks (DQN), our system autonomously tunes network parameters across macro, micro, and pico cells, adapting to the dynamic distribution in a heterogeneous network environment. The agent is tasked with optimizing several Key Performance Indicators (KPIs) such as throughput, latency, interference, and Quality of Service (QoS). Each cell in the network can perform actions such as adjusting power levels, changing handover thresholds, allocating bandwidth, and performing interference mitigation. Our approach demonstrates significant improvements in user experience, resource utilization, and network efficiency over traditional static optimization methods. The results show that the proposed reinforcement learning -based algorithm not only reduces latency and interference but also ensures better load balancing and throughput optimization across heterogeneous cells.

The rapid increase in IoT (Internet of Things) devices in 5 G networks poses an increasing challenge for managing uplink (UL) traffic, especially in dense and heterogeneous scenarios. Traditional uplink management strategies may not achieve fairness or efficiency in resource allocation under realistic, dynamic conditions related to IoT traffic. This paper provides a procedural framework for Downlink and Uplink Decoupling (DUDe) which produces performance benefits for the uplink in 5G networks leveraging IoT devices. The framework is examined via simulation in MATLAB in a variety of scenarios and the performance of DUDe is compared with existing uplink management strategies in the literature. The results presented demonstrate that DUDe achieves substantial gains in fairness with regard to resource allocation, with minimal deterioration in spectral efficiency, and moderate impact on throughput. Finally, operational challenges related to deploying DUDe in practice (e.g. hardware compatibility and operational complexity) are considered, along with potential solutions. The paper can be seen as an informative reference for future potential practical implementation of DUDe in real world 5G IoT networks.

The advent of 5 G technology has ushered in a new era of wireless communication, characterized by its promise of high data rates, low latency, and enhanced connectivity. In this context, Multiple-Input Multiple-Output (MIMO) systems have emerged as a key enabler, leveraging advanced antenna arrays to simultaneously serve multiple users with increased spectral efficiency. This paper investigates the dynamic resource allocation problem in a MIMO 5 G environment, where each user possesses distinct bandwidth requirements. The focus is on optimizing user allocation while considering the limited bandwidth and user capacity of base stations. By harnessing the power of deep learning techniques, the proposed solution aims to efficiently manage the allocation of users to base station antennas, thereby maximizing overall network performance while accommodating heterogeneous user demands.

Massive MIMO (Multiple Input Multiple Output) is a fundamental technique for improving the efficiency of 5G wireless networks. At the base station, it calls for the use of numerous antennas—usually in the dozens or even hundreds. In addition to better coverage and less interference, this enables a large increase in the amount of data that can be delivered and received simultaneously. By enabling more precise signal transmission and reception, Massive MIMO can also result in significant energy savings. The use of optimization techniques can further improve the performance of 5G networks. The aim of this paper is to investigate a signal quality optimization technique for MIMO in which users are allocated to antennas according to different algorithms. For our research, the DeepMIMO simulator produced a dataset that sets up all necessary parameters. In our study, we examine different techniques for user allocation in 5G MIMO Networks. We conclude that transforming the problem of user allocation to a linear assignment problem in order to find the most efficient connection between the users and the base stations is one of the best ways to optimize user allocation.

By introducing 5G networks in our lives, we are faced with the challenge to lower energy consumption, which is expected to increase significantly. As a result, the communications sector must devise solutions to improve the energy efficiency of 5G networks while maintaining spectrum performance. We propose a Machine Learning Mechanism that provides new sleep mode functionalities, that reduce energy consumption during idle hours, on small cells. We will describe our model and examine its performance using data collected from a simulated environment. Furthermore, we present the results of our findings and conclude that such models are necessary for the introduction of 5G networks. Lastly, possible future steps, are discussed.

Search and Rescue (SAR) operations can be vastly benefited by the use of IoT and especially by Low Power Wide Area Networks (LPWAN) technologies, such as Long Range (LoRa). In this framework, the wearable device-based Search And Rescue system (WeSAR) project has been created. The main goals that WeSAR tries to improve are the localization accuracy and the energy efficiency of the wearable device. In this paper, the authors propose an energy-efficient mechanism for LoRa networks, taking into consideration the energy of a real wearable device, containing multiple sensors in a SAR scenario. In this work, we simulate the LoRa network, taking into consideration the various states of a wearable device and the impact of the sensors on the energy consumption, in order to have insights into the mechanism’s efficiency with multiple nodes, up to 500 nodes. The experiment results reveal significant reductions in the energy consumption of the wearable device and improvement of battery life, in urban and suburban conditions, and in stationary and no stationary node mobility models.

Machine learning is an extremely efficient technique for solving complex problems without the use of traditional programming but rather enabling machines to learn from an input of data and train them to cope with various problems. The rapid growth in the number of active mobile devices, mobile applications and services dictates an efficient utilization of mobile and wireless networking infrastructure. Communication networks need to evolve and valorize machine learning methods in order to process large volumes of data without introducing excessive time delay in these computations. Upcoming 5G systems are expected to be the first network infrastructure to support exploding mobile traffic volumes and machine learning techniques can be used in order to help manage the rise in data volumes. We present a mechanism for resource allocation in mobile and wireless networks, that effectively utilizes machine learning techniques.

The upcoming 5G networks require an advanced planning in terms of coordinating various mechanisms to achieve the highly expected performance growths that they pledge. This coordination becomes more challenging due to the increased density in urban environments of the deployment of small radius base stations, such as femtocells. In this paper we test our proposed mechanism for sleep mode power control in femtocell networks, over a widely used simulated traffic model, adjusted to our scenario. Our sleep mode strategy has been developed for femtocell clusters with the goal of reducing the number of operating femtocells without compromising the data rate performance of their subscribers. Our simulations reaffirm the benefits of our algorithm, especially the reduced number of operating femtocells and the increased offered capacity, when tested in realistic environments.

The evolution of 5G mobile networks is expected to be comprised of small cell deployments within spitting distance of existing macrocell infrastructures. The small cells adoption, which promises to offer an economical solution for improved coverage and data rate, appears to be the key factor at improving network cooperation and system performance. In this paper, we evaluate the User-Centric model for 5G networks, targeted at improving communication between user terminal and Base Stations across all layers. We suggest a cost-effective, resource-aware method for improved mobile outdoor coverage and overall network capacity while fully respecting the user's Quality of Service, by decoupling the overall network into downlink and uplink networks. The proposed algorithm determines how the network users in both networks will efficiently connect to a Base Station. The network performances are evaluated in terms of data rates enhancements, association outcome and preservation of the Quality of Service for each user. Our low-complexity algorigthm ultimately manages to serve the vast majority of the users placed inside an ultra-dense network and achieve perfect preservation of Quality of Service, regardless of the number of active users.

Demanding goals have already been described concerning the next generation of mobile networks. In order to address these requirements, novel technologies are introduced or new concepts are integrated into conventional ones. In this paper, a modified Distributed Antenna System (DAS) architecture is described and a Sensitivity Analysis (SA) indicates which of the network cost parameters are the most influential ones concerning this model. Several hardware components are replaced with Network Function Virtualization (NFV) techniques, which are introduced, so as to contribute in reducing capital and operational expenses. The model is described mathematically, is compared and contrasted with the conventional model proposed by authors in past research activity. Simulation scenarios help concluding into fundamental results concerning the most dissuasive cost factors e.g. bandwidth, frequency, capacity, coverage, etc.

Next generation of mobile technologies demands high date rates and low round trip times. Therefore, we analyze deployments that offer these performance capabilities. We consider the fundamental issue of the expenses of the network's installation, maintenance and operation. We calculate the costs of Distributed Antenna Systems (DAS) and small cells by describing updated cost models for each one. We present a Sensitivity Analysis of certain types of cost variables and parameters including the existing bandwidth, the running costs, the interest rate, the base station, the equipment, the power consumption, the backhaul, the implementation costs and Throughput Density. We include a variable cost provision for the year 2016 and beyond, and conduce several experiments, based on the upper analysis, by considering many different parameter prices and introducing the Throughput Density. We calculate the Total Cost of Ownership (TCO), the Capital (CAPEX) and the Operational (OPEX) expenditures. Finally, we are led to important conclusions by comparing the two main technologies costs and evaluating the cost parameters and variables that will lead future researchers to suggest ways to reduce the higher costs.

Broadband is a public utility with positive effects on competitiveness, employment and growth. Although evidence shows that broadband development is increasing, this increment is not homogeneous between urban and rural areas. The main cause is the high cost for deploying next generation networks in rural areas, and especially the cost linked to civil engineering works. In order to overcome the investment challenges arising in the context of broadband deployment, the European Commission made mandatory the sharing of existing telecommunication and non-telecommunication infrastructures and facilities. This paper proposes and presents a novel tool that enables the estimation of the expected savings from exploiting existing infrastructures when deploying a broadband network. This is followed by a number of general principles and recommendations that policy makers and national authorities could embrace to diminish deployment costs and promote broadband deployment.

While online information sources are rapidly increasing in amount, so does the daily available online news content. Several approaches have being proposed for organizing this immense amount of data. In this work we explore the integration of multiple information retrieval techniques, like text preprocessing, n-grams expansion, summarization, categorization and item/user clustering into a single mechanism designed to consolidate and index news articles from major news portals from around the web. Our goal is to allow users to seamlessly and quickly get the news of the day that are of appeal to them via our system. We show how, the application of each one of the proposed techniques gradually improves the precision results in terms of the suggested news articles for a number of registered system users and how, aggregately, these techniques provide a unified solution to the recommendation problem.

Broadband is starting to be deemed by many as a public utility and several countries have already recognized it as a civil right. The European Commission (EC) acknowledging the significance of broadband services for the improvement of citizen welfare and its economic benefits, has put in place targets for the diffusion of broadband to all citizens and businesses in the European Union. This paper, comparatively assesses the current state of affairs in broadband and digital public services in selected South East Europe countries in order to identify weaknesses and highlight strengths and to produce knowledge resources and provide insights that will support informed decision making including strategy and policy planning. It builds on three surveys that took place in the second quarter of 2013 and evidence gathered from seven South East Europe countries.

The main focus of this work is the effort to minimize the power consumption on mobile devices such as notebooks, netbooks, tablets, tablets, smartphones, etc. by adjusting the transmission power of the wireless card, thus extending the battery life. In order to achieve that, we provide a mechanism (which we call Signal Adaptation Mechanism - SAM) that optimizes the power depending on the quality of the connection. This mechanism measures the quality of the transmission and adjusts the transmission power accordingly, by utilizing an expanded array of metrics along the Received Signal Strength Indicator (RSSI), for more accurate estimation. It also aims at easy implementation on various wireless adapters. In order to evaluate, fine-tune and improve the mechanism, a list of experiments has been performed. These experiments were conducted on a real (as opposed to simulated) ad-hoc network, where the nodes of the networks followed varying moving patterns.

A crucial point on the delivery of multicast content over mobile multicast networks is the utilization of Forward Error Correction (FEC) codes on the application layer (AL-FEC) so as to introduce robustness against arbitrary erasures on different recipients without the need of inefficient common error control methods based on data retransmission. FEC is a feedback free error recovery method where the sender introduces redundant data in advance with the source data enabling the recipients to recover from different arbitrary packet losses. The main issue on the efficient application of AL-FEC protection is the adaptation of the introduced redundancy to the current network conditions, in order to avoid network resources wastage ensuring at the same time sufficient transmission robustness. Based on this, in this work we present an adaptive weighted online algorithm aiming at the efficient application of RaptorQ AL-FEC codes over mobile multicast services. The proposed algorithm adapts the introduced AL-FEC transmission overhead exploiting at first the reception reports ability defined by several mobile multicast standards and thereafter the performance properties of the newly introduced RaptorQ FEC codes. We introduce the competitive framework of the efficient application of AL-FEC protection over mobile multicast networks, in the context of which, we design and analyze the adaptive online weighted algorithm and we further provide a series of simulation results to analyze the performance of the proposed scheme.

In this paper we present a feedback-based adaptation mechanism that adjusts the transmission power of a wireless card on commodity PCs depending on the quality of the connection. Our purpose is to manage the available power in order to achieve lower power consumption without negatively affecting the user's perception of connection quality. We based our implementation on an existing theoretical model and focused on resolving problems and removing assumptions which made it inefficient in real life implementation. The initial model manages to minimize the power consumption in networks with exactly two nodes. In this paper, we extend the model to consider the possibility of the existence of a base station, where any number of nodes can be connected. Our objectives for the base station are to minimize the power consumption and guarantee continuous connectivity for all mobile nodes. We implement the adaptation mechanism for a specific adapter with open sources drivers thus allowing necessary modifications. We conduct a number of real world experiments. The results indicate that power consumption can be significantly reduced for nodes that are either almost stationary or slowly moving (e.g. at walking speed), without any significant increase in packet loss. The results are quite important as nowadays mobile devices with limited battery life time use tethering to become base stations for other devices like in ad-hoc networks.

Reliability control is a key concern on the evolution of real-time mobile multicast services. To this direction the use of forward error correction (FEC) on the application layer is widely adopted in several mobile multicast standards. FEC is a feedback free error control method where the transmitter introduces in advance redundant information to enable receivers recovering data erasures. On multicast delivery and especially on the time constrained streaming delivery where retransmission-based error recovery methods are not feasible, the most suitable error control method is the use of application layer forward error correction (AL-FEC) codes. In this work, we introduce a novel AL-FEC deployment policy over mobile multicast standards utilizing online algorithms. We aim on the efficient application of AL-FEC protection with RaptorQ codes over multicast streaming delivery in the context of competitive analysis. We provide a competitiveness analysis model of AL-FEC application over mobile multicast real-time environments and we introduce an innovative online algorithm adjusting the introduced redundancy of AL-FEC protection according to the FEC encoding parameters in order to satisfy the individual constraints of a multicast streaming delivery.

Abstract: This paper presents the enhancements that we have done on the TRAFIL (TRAce FILe) framework, which significantly extend its capabilities in the areas of simulation design and execution. In particular, TRAFIL now offers the possibility to design, create, execute and review NS-2 simulation scenarios, on top of its ex-isting post-simulation trace analysis functionalities. The enhancements make TRAFIL a complete wrapper around the NS-2 simulator, allowing the user to perform all steps from pre-simulation design to actual simu-lation execution in an automated way and fast and convenient post-simulation analysis of potentially large amount of data. The paper describes the new TRAFIL architecture and how these enhancements were im-plemented with the goal of relieving NS-2 users from the often cumbersome tasks of script writing and vali-dating, while also enabling them at to go behind the TRAFIL environment and into the simulator internals at any time. The paper presents the new GUI functionalities developed for that purpose, the approach that we took for their design and how these fit in the overall TRAFIL architecture.

A crucial point on the successful deployment of multicast services is the enhanced reliability by means of advanced error control schemes. To this direction Third Generation Partnership Project (3GPP) has standardized exclusively for Multimedia Broadcast/Multicast Services (MBMS) the use of a Forward Error Correction (FEC) mechanism on the application layer based on Raptor codes. Since the standardized systematic, fountain Raptor code is now considered obsolete, the emergence of a new variant of Raptor codes, named RaptorQ, provides enhanced capabilities for mobile multicast services. In this paper, we provide a performance comparison of the standardized Raptor Application Layer FEC (AL-FEC) scheme with the very promising RaptorQ FEC code. We examine the enhancements that RaptorQ introduces on the AL-FEC protection robustness, providing a thorough performance analysis in comparison with the current Raptor FEC scheme. Furthermore, in order to verify the improved performance of RaptorQ, we provide several simulation results utilizing the ns-3 environment, considering the application of both the examined AL-FEC schemes over multicast services for next generation mobile networks.

Third Generation Partnership Project (3GPP) introduced Multimedia Broadcast/Multicast Services (MBMS), in order to efficiently deliver the same content to multiple users over mobile cellular networks. To enhance the download and streaming delivery robustness against packet losses, 3GPP proposes the use of Forward Error Correction (FEC) on the application layer. The Application Layer FEC (AL-FEC) scheme that 3GPP standardized is based on the systematic, fountain Raptor code. In this work, in response to the emergence of an enhanced FEC scheme, we provide a performance evaluation of the existing standardized AL-FEC scheme with the newly introduced RaptorQ code. Introducing a variety of simulation experiments, we analyze the performance behavior of each AL-FEC scheme considering several FEC encoding parameters. Furthermore, we try to verify the improvements that have emerged in AL-FEC providing enhanced capabilities in multicast services over next generation mobile networks.

With the rapid explosion of online news articles, predicting userbrowsing behavior using collaborative filtering techniques has gained much attention in the web personalization area. However, common collaborative filtering techniques suffer from low accuracy and performance. This research proposes a new personalized recommendation approach that integrates user and text clustering based on our developed algorithm, W-kmeans, with other information retrieval techniques, like text categorization and summarization in order to provide users with the articles that match their profiles. Our system can easily adapt over time to divertive user preferences. Furthermore, experimental results show that by aggregating multiple other information retrieval techniques like categorization, summarization and clustering, our recommender generates results that outperform the cases when clustering is not applied.

One of the most attractive features of Massively MuItiplayer Online Games (MMOGs) is the possibility for users to interact with a large number of other users in a variety of collaborative and competitive situations. Garners within an MMOG typically become members of active communities with mutual interests, shared adventures, and common objectives. This demonstration presents a peer-to-peer live video system that enables MMOG players to stream screen-captured video of their game. Players can use the system to show their skills, share experience with friends, or coordinate missions in strategy games.

In cellular systems, Fractional Frequency Reuse (FFR) partitions each cell into two regions; inner region and outer region and allocates different frequency band to each region. Since the users at the inner region are less exposed to inter-cell interference, the frequency resources in each inner region can be universally used. Based on this frequency band allocation, FFR may reduce channel interference and offer large system capacity. This paper proposes a mechanism that selects the optimal FFR scheme based on the user throughput and user satisfaction. In detail, the mechanism selects the optimal size of the inner and outer region for each cell as well as the optimal frequency allocation between these regions that either maximizes the mean user throughput or the user satisfaction. The mechanism is evaluated through several simulation scenarios.

With the booming of multimedia services, the 3rd Generation Partnership Project (3GPP) has introduced the evolved Multimedia Multicast/Broadcast Service (e-MBMS) feature for LTE systems. The main objective of MBMS is to introduce real broadcast distribution capabilities into cellular systems. This purposed 3GPP to introduce the MBMS over a Single Frequency Network (MBSFN) operation. In this work we investigate the provision of MBMS service over a combination of MBSFN and PTM transmission schemes. We focus on the file repair procedure, because the distribution of binary data via MBMS must result in 100% error-free downloaded files. In order to achieve this goal, MBMS offers a Forward Error Correction (FEC) mechanism. Our simulation results show that there are some file repair schemes that achieve better performance as far as different network configurations are concerned. Furthermore, we compare all the file recovery methods and evaluate them against various network parameters in a realistic simulation environment.

We present in this work the performance evaluation of MPEG-4 video transmission with our proposed single rate multicast protocol named Adaptive Smooth Multicast Protocol (ASMP). ASMP key attributes are: (a) adaptive scalability to large sets of receivers, (b) TCP-friendly behavior, (c) high bandwidth utilization, and finally (d) smooth transmission rates which are suitable for multimedia applications. We evaluate the performance of ASMP under an integrated simulation environment which extends ns-2 and Evalvid-RA to the multicast domain with the use of the RTP/RTCP protocols. Simulations conducted under this environment combine the measurements of network-centric along with video quality metrics. This “joint” evaluation process provides a better understanding of the benefits and limitations of any proposed protocol for multimedia data transmission.

We present the dynamic web personalization and document grouping infrastructure for meta-portals and the evaluation of the mechanism on peRSSonal, a system that collects articles from news portals and blogs worldwide. A meta-portal is an informational node where articles from different sources are collected and presented in a categorized and personalized manner. The web personalization mechanism is based on dynamic creation and update of user profile according to the user's preferences when browsing and on user grouping details. Assuming that required information, such as article tagging, keywords to categories matching and articles to categories relation is already part of the meta-portal we present a novel mechanism that can build and maintain a user profile which is formed without disturbing the user. Furthermore, we describe the real-time user centered document grouping mechanism that is implemented to support the web personalization system and present the experimental evaluation of the whole system.

The key feature for the provision of Multimedia Broadcast/Multicast Services (MBMS) in Long Term Evolution (LTE) networks is the Multimedia Broadcast over a Single Frequency Network (MBSFN). On the other hand, the use of Forward Error Correction (FEC) in mobile multicast transmission has significant advantages and the 3rd Generation Partnership Project (3GPP) has adopted the application layer FEC in the MBMS standard. In this paper, we investigate the impact of the application layer FEC over the MBSFN delivery method.

Long Term Evolution (LTE) is the latest step towards the 4th generation (4G) of radio technologies designed to increase the capacity and speed of mobile communications. To support Multimedia Broadcast/Multicast Services (MBMS), LTE offers the possibility to transmit Multimedia Broadcast multicast service over a Single Frequency Network (MBSFN), where a time-synchronized common waveform is transmitted from multiple cells for a given duration. In this paper we analytically present the MBSFN delivery method and evaluate its performance. The critical parameters of primary interest for the evaluation of the scheme are the packet delivery cost and its scalability. To this direction, a telecommunication cost analysis of the MBMS service is presented based on the transmission cost over the air interface, as well as the costs of all interfaces and nodes of the MBSFN architecture. Since the performance of the MBSFN scheme mainly depends on the configuration of the LTE network that is under investigation, we consider different network topologies, MBSFN deployments and user distributions.

Long Term Evolution (LTE) constitutes the latest step before the 4th generation (4G) of radio technologies designed to increase the capacity and speed of mobile communications. To support Multimedia Broadcast/Multicast Services (MBMS), LTE offers the possibility to transmit Multimedia Broadcast multicast service over a Single Frequency Network (MBSFN), where a time-synchronized common waveform is transmitted from multiple cells for a given duration. This enables over-the-air combining, thus improving the Signal to Interference plus Noise Ratio (SINR) and spectral efficiency (SE) significantly compared to conventional MBMS operation. In this paper, we analytically calculate the SE performance achieved in a MBSFN area for a dynamically changing user topology and different modulation and coding schemes (MCS). Finally, based on the SE measurement, we determine the MCS scheme that either maximizes or achieves a target SE for the corresponding user distribution.

Following the trends of our era, Games At Large IST Project introduces an innovative platform for running interactive, rich content multimedia applications over a wireless local area network. Games@Large project's vision is to provide a new system architecture for interactive multimedia which will enhance existing CE devices such as, set top boxes (STB), small screen and other devices, which are lacking both the CPU power and the graphical performance to provide a rich user experience. This paper presents the input command transferring module that provides encryption capabilities for ensuring the security of the transmitted sensitive user data. In a nutshell, the client software when capturing input from a keyboard device encrypts the commands that are transmitted over a wireless local area network, using a public key encryption scheme and the server is responsible for decrypting and executing the commands to the corresponding game application.

We present ldquoadvaRSSrdquo crawling mechanism which is created in order to support peRSSonal, a mechanism used to create personalized RSS feeds. In contrast to the common crawling mechanisms our system is focalized on fetching the latest news from the major and minor portals worldwide by utilizing their communication channels. The challenge between ldquoadvaRSSrdquo and a usual crawler is the fact that the news is produced in a random order any time of the day and thus the freshness of the offline collection can be measured even in minutes. This means that the system has to be updated with news every single time they occur. In order to achieve this we utilize the communication channels that exist on the modern architecture of the WWW and more specifically in almost every modern news portal. As the RSS feeds are used by every major and minor portal it is possible to keep our crawler up to date and retain a high freshness of the ldquooffline contentrdquo that is maintained in our systempsilas database by applying algorithms in order to observe the temporal behaviour of each RSS feed.

Personalized Web Search becomes nowadays a promising option in the field of Information Retrieval and search engines design by improving both output quality and user experience. In this paper, we present and evaluate the subsystem, which conducts the Advanced and Personalized search of PeRSSonal, a web-based mechanism for the retrieval, processing and presentation of articles and RSS feeds collected from major news portals of the Internet. The proposed technique uses information explicitly provided by the user in his profile as well as information that the mechanism can learn from the userpsilas behavior during his search and browsing sessions in the system. As this behavior dynamically evolves, the same happens to the userpsilas interests under the prism of the search engine. By adopting this user-centric approach, we manage to present the user with better-refined and more focused results, incorporating his personal preferences to the output. The algorithm operates not in a stand-alone manner but it co-operates and binds with the rest of modules of PeRSSonal in order to accomplish maximum integration with the system. Furthermore, we introduce an enhancement in the search function, based on cached results from past search sessions of each user individually.

Deploying a generalized, multi-functional mechanism that produces good results for personalizing summarized and categorized news articles, seems to be a panacea for most of the text-based, information retrieval needs. In this paper, we present the personalization algorithm, as well as a client side application that are used as an extension to an already constructed system, PeRSSonal, in order to deliver summarized and pre-categorized news articles to the user.

We introduce Adaptive Smooth Simulcast Protocol (ASSP) for simulcast transmission over best-effort networks. ASSP is a new multiple-rate protocol that implements a single rate TCP-friendly protocol as the underlying congestion control mechanism for each simulcast stream. ASSP is build on top of the RTP/RTCP protocol and exploits the RTCP sender and receiver reports for the dissemination of feedback information. The key attributes of ASSP are: a) TCPfriendly behavior, b) adaptive per-stream transmission rates, c) adaptive scalability to large sets of receivers and finally d) smooth transmission rates that are suitable for multimedia applications. We evaluate the performance of ASSP and investigate its behavior through simulations conducted with the network simulator software (ns2).

The provision of rich multimedia services, such as Mobile TV, is considered of key importance for the Long Term Evolution (LTE) proliferation in mobile market. To this direction, Evolved - Multimedia Broadcast/Multicast Service (E-MBMS) that targets at the efficient delivery of multimedia data from a single source entity to multiple destinations, is envisaged to play an instrumental role during LTE standardization process. However, both LTE and E-MBMS performance are limited by the base station's transmission power. As an aftermath, efficient power allocation techniques should be implemented so as to ensure the mass provision of multimedia applications to mobile users. This paper proposes a novel mechanism for efficient radio bearer selection during E-MBMS transmissions in LTE networks. The proposed mechanism is based on the concept of transport channels combination in any cell of the network. Most significantly, the mechanism exploits the performance enhancements emerged from Multiple Input Multiple Output (MIMO) antennas used in LTE networks and manages to efficiently deliver multiple E-MBMS sessions. The proposed mechanism is thoroughly evaluated and compared with several radio bearer selection mechanisms existing in bibliography.

In the frame of the Long Term Evolution (LTE) of mobile networks, the provision of rich multimedia services, such as Mobile TV, is considered of key importance for the LTE proliferation in mobile market. To this end, Multimedia Broadcast/Multicast Service (MBMS) is envisaged to play an instrumental role during LTE standardization process. MBMS was introduced in the Release 6 of Universal Mobile Telecommunication System (UMTS) in order to deliver multimedia data from a single source entity to multiple destinations. However, downlink capacity in such networks is limited by base station transmission power. As an aftermath, in MBMS efficient power allocation techniques should be implemented so as to ensure the mass provision of multimedia applications to mobile users. In this paper we propose a power control scheme for efficient selection of MBMS bearers. The proposed mechanism on the one hand manages to economically utilize power resources during MBMS transmissions, while on the other hand exploits the performance enhancements emerged from Multiple Input Multiple Output (MIMO) antennas used in LTE networks. Simulation results indicate that the proposed scheme results to significant power and capacity improvements.

This paper proposes a power control mechanism for the efficient radio bearer selection in the multimedia broadcast/multicast service (MBMS) framework of Universal Mobile Telecommunications System (UMTS). The selection of the most efficient transport channel in terms of power consumption is a key point for MBMS enabled UMTS networks, since a wrong transport channel selection for the transmission of the MBMS data could result to a significant decrease in the total capacity of the network. Different UMTS transport channels and power saving techniques are examined and an algorithm that selects the most efficient combination of the above parameters is proposed. The proposed MBMS power control mechanism selects the transport channel that minimizes the base station's transmission power in every cell of the network that serves multicast users.

Abstract Along with the widespread deployment of the Third Generation (3G) cellular networks, the fast‐improving capabilities of the mobile devices, content, and service providers are increasingly interested in supporting multicast communications over wireless networks and in particular over Universal Mobile Telecommunications System (UMTS). To this direction, the Third Generation Partnership Project (3GPP) is currently standardizing the Multimedia Broadcast/Multicast Service (MBMS) framework of UMTS. In this paper, we present an overview of the MBMS multicast mode of UMTS. We analytically present the multicast mode of the MBMS and analyze its performance in terms of packet delivery cost under various network topologies, cell types, and multicast users' distributions. Furthermore, for the evaluation of the scheme, we consider different transport channels for the transmission of the multicast data over the UMTS Terrestrial Radio‐Access Network (UTRAN) interfaces. Finally, we propose a scheme for the efficient radio bearer selection that minimizes total packet delivery cost. Copyright © 2008 John Wiley & Sons, Ltd.

As the evolution of computer technology introduces new advances in networks among others, online gaming becomes a new trend. Following the trends of our era, Games At Large IST Project introduces an innovative platform for running interactive, rich content multimedia applications over a Wireless Local Area Network. Games at Large project's vision is to provide a new system architecture for Interactive Multimedia which will enhance existing CE devices such as, Set Top Boxes (STB), Small Screen and other devices, which are lacking both the CPU power and the graphical performance to provide a rich user experience. This paper presents the controllers' subsystem of the innovative mechanism that will be implemented in the context of Games at Large project. More specifically, it presents the general architecture of the complete system and focuses on the "capturing" and "execution of commands" modules at the different clients and the remote execution of the commands on server side. The client software captures the input from the different input devices, sends the commands over a Wireless Local Area Network and the server is responsible for receiving and executing the commands to the corresponding application.

The demand for wireless multimedia communications thrives in todaypsilas consumer and corporate market. The need to evolve multimedia applications and services is at a critical point given the proliferation and integration of wireless systems. multimedia broadcast multicast services (MBMS) was introduced in third generation partnership project (3GPP) Release 6 in order to more efficiently use network and radio resources for the transmission of multimedia data, both in the core network and most importantly in the air interface of UTRAN (UMTS terrestrial radio access network). However, several obstacles, regarding the high power requirements, should be overcome for the realization of MBMS. The fact that Node Bpsilas transmission power is a limited resource and must be shared among all MBMS users in a cell indicates the need for power control during MBMS transmissions. Several techniques, such as dynamic power setting and macro diversity combining, have been proposed in order to reduce the power requirements of delivering multicast traffic to MBMS users. This paper examines the efficiency of the utilization of these power saving techniques, by presenting simulation results that will reveal the amount of power that is saved.

Multimedia Broadcast/Multicast Service (MBMS) and High-Speed Downlink Packet Access (HSDPA) are two key technologies that constitute a significant step towards the Mobile Broadband. MBMS was introduced by the third Generation Partnership Project (3GPP) in order to support broadcast and multicast communication over wireless networks and in particular over Universal Mobile Telecommunications System (UMTS). Concurrently, HSDPA aims to ensure the transmission of high peak data rates and increase system capacity. In this paper we evaluate the performance of MBMS multicast transmission over the premier transport channel used in HSDPA, named High Speed-Downlink Shared Channel (HS-DSCH). Due to the fact that downlink transmission power is the scarcest resource in UMTS networks, the evaluation is performed through an analytical dimensioning of the MBMS downlink transmission power. Furthermore, the impacts of power allocation on MBMS capacity are investigated.

This paper proposes a novel mechanism for efficient power control during multicast transmissions in Beyond 3rd Generation (B3G) mobile networks. The mechanism utilizes optimally the available power resources of Universal Mobile Telecommunication System (UMTS) base stations, resulting to network capacity maximization. The proposed mechanism is based on the concept of transport channels combination (point-to-point and/or point-to-multipoint radio bearers) in any cell/sector of the network in which Multimedia Broadcast/Multicast Service (MBMS) users are residing. In particular, the transport channel combination that minimizes the transmission power of the base station is selected for the transmission of the MBMS traffic to the corresponding cell. The mechanism is evaluated through several realistic scenarios and the results indicate the ability of the mechanism to utilize optimally the radio resources of the network. Furthermore, our approach is compared with several power control mechanisms existing in the bibliography, including the 3rd Generation Partnership Project (3GPP) approaches (presented in 3GPP TS 25.346 and 3GPP TR 25.922), in order to highlight the enhancements that it provides.

In Universal Mobile Telecommunication System (UMTS), the downlink capacity is limited by the base station transmission power. Therefore, power control plays an important role to minimize the transmitted power shared among unicast and multicast users within a cell. In Multimedia Broadcast/Multicast Service (MBMS), power control targets to the efficient utilization of radio and network resources. However, the expected high demand for such services stresses the need for an efficient scheme, capable of dynamically allocating radio resources to parallel MBMS sessions. This paper proposes a power control mechanism for efficient MBMS session assignment in next generation UMTS networks. The mechanism shares efficiently the available power resources of UMTS base stations to MBMS sessions running in the network Furthermore, the mechanism is evaluated through several realistic scenarios and the results indicate the ability of the mechanism to utilize efficiently the radio resources and to ensure the service continuity when parallel MBMS services running in the network.

Abstract It is known that multicasting is an efficient method of supporting group communication as it allows the transmission of packets to multiple destinations using fewer network resources. Along with the widespread deployment of the third generation cellular networks, the fast‐improving capabilities of the mobile devices, content and service providers are increasingly interested in supporting multicast communications over wireless networks and in particular over Universal Mobile Telecommunications System (UMTS). Multicasting is a more efficient method of supporting group communication than unicasting or broadcasting, as it allows transmission and routing of packets to multiple destinations using fewer network resources. In this paper, the three above mentioned methods of supporting group communication are analyzed in terms of their performance. The critical parameters of primary interest for the evaluation of any method are the packet delivery cost and the scalability of the method. Copyright © 2006 John Wiley & Sons, Ltd.

The partitioning constitutes one of the basic problems that need to be handled in distributed virtual environments for maintaining consistency among users' view of the virtual scene and for optimizing the performance of the system. This paper presents an approach for handling the partitioning problem, which is based on objects' attributes. In particular, the approach proposes a technique, which takes into account the degree of interaction that the objects of the virtual environment carry for predicting future avatar behavior. This prediction of avatars' behavior based on objects ' attributes defines the initial partitioning of the virtual space.

Multimedia Broadcast Multicast Services (MBMS), introduced in Third Generation Partnership Project (3GPP) Release 6, is a point-to-multipoint downlink bearer service that addresses the need for the efficient usage of the expensive radio resources. Power control is one of the most important aspects in MBMS due to the fact that Node B's transmission power is a limited resource and must be shared among all MBMS users in a cell. Consequently, the analysis of transmitted power plays a fundamental role in the planning and optimization process of Universal Mobile Telecommunications System (UMTS) radio access networks. This paper investigates several factors affecting Node B's transmission power levels such as, cell deployment, propagation models, Quality of Service (QoS) requirements, users' distributions and mobility issues. Finally, different transport channels for the transmission of the multicast data over the UTRAN interfaces are considered.

Along with the widespread deployment of the third generation cellular networks, the fast-improving capabilities of the mobile devices, content and service providers are increasingly interested in supporting multicast communications over wireless networks and in particular over universal mobile telecommunications system (UMTS). To this direction, the third generation partnership project (3 GPP) is currently standardizing the multimedia broadcast/multicast service (MBMS) framework of UMTS. In this paper, we present an overview of the MBMS multicast mode of UMTS. We analytically present the multicast mode of the MBMS and analyze its performance in terms of packet delivery cost under various network topologies, cell types and multicast users' distributions. Furthermore, for the evaluation of the scheme, we consider different transport channels for the transmission of the data over the UTRAN interfaces.

This paper proposes a business model for the successful operation of the currently developing broadband metropolitan area networks in Greece. Having recorded and examined relevant international practices, we describe in detail the way that these networks should be managed, operated, maintained and expanded. Taking into consideration that these infrastructures will alter the broadband map of Greece widely, that Greece currently has one of the lowest broadband penetration percentages in Europe and that the proper exploitation of the networks to be deployed could boost the demand for broadband connections and applications, the proposition of the business model appears to be of vital importance. We present the proposed business model in detail including information regarding network management and network expansion of the broadband metropolitan networks and viability issues regarding the authority which will manage the broadband metropolitan networks.

Multimedia Broadcast Multicast Services (MBMS) was introduced in Third Generation Partnership Project (3GPP) Release 6 in order to address the need for the efficient usage of the expensive radio resources. The goal of this effort is to support downlink streaming and download-and-play type services to large groups of users. From the radio perspective, MBMS includes point-to-point (PtP) and point-to-multipoint (PtM) modes. The fact that Node B's transmission power is a limited resource and must be shared among all MBMS users in a cell indicates the need for power control during an MBMS service. Consequently, the analysis of the transmitted power plays a fundamental role in the planning and optimization process of Universal Mobile Telecommunications System (UMTS) radio access networks. In this paper we investigate the factors that affect the Node B's transmission power levels during an MBMS session, such as, cell deployment, propagation models, users' distributions and mobility issues. To this direction, the transport channels in the downlink, currently existing in UMTS which could be used to transmit the multicast data over the UMTS Terrestrial Radio-Access Network (UTRAN) interfaces are examined.

Distributed virtual environments tend to become a de facto solution for large-scale networked virtual environments. One of the key issues and problems that need to be handled in the design of a scalable and effective distributed virtual environment system is the partitioning problem, which refers to the efficient assignment of the system's workload to the available resources of the system. This paper presents an object driven partitioning approach based on the partitioning algorithm of Lui & Chan, who proposed a three step technique for balancing the workload among the servers of the Distributed Virtual Environment.

Multicasting is an efficient way for delivering rich multimedia applications to large user groups as it allows the transmission of packets to multiple destinations using fewer network resources. Content and service providers are increasingly interested in supporting multicast communications over wireless networks and in particular over universal mobile telecommunications system (UMTS). To this direction, the third Generation Partnership Project (3 GPP) is currently standardizing the multimedia broadcast/multicast service (MBMS) framework of UMTS. In this paper, we present an overview of the MBMS multicast mode of UMTS. We analytically present the multicast mode of the MBMS and analyze its performance in terms of packet delivery cost under various network topologies, cell environments and multicast users' distributions. Furthermore, for the evaluation of the scheme, we consider different transport channels for the transmission of the data over the UTRAN interfaces and propose a cost based scheme for the efficient radio bearer selection that minimizes the packet delivery cost.

This paper proposes a power control scheme for the efficient radio bearer selection in the Multimedia Broadcast/Multicast Service (MBMS) framework of Universal Mobile Telecommunications System (UMTS). The choice of the most efficient transport channel in terms ofpower consumption is a key point for the MBMS since a wrong transport channel selection for the transmission of the MBMS data could result to a significant decrease in the total capacity of the system. Diferent UMTS transport channels are examined and an algorithm that defines the switching point between dedicated and common radio bearers is proposed The proposed MBMSpower control scheme selects the transport channel that reduces the Node B's transmission power in every cell of the network with multicast users.

The scheme of real time streaming video is one of the newcomers in wireless data communication, raising a number of new requirements in both telecommunication and data communication systems. This scheme is applied when the user experiences real time multimedia content. Rate control is an important issue in video streaming applications for both wired and wireless networks. A widely accepted rate control method in wired networks is equation based rate control. In this work, we focus on a mechanism for equation based congestion control for video transmission over WCDMA networks. With our mechanism, the sender explicitly adjusts its sending rate as a function of the measured rate of loss events, the round trip time and the packet size. Furthermore, we examine the performance of UMTS air interface for real time video transmission using real time protocols, through a number of experiments.

Carefully designed and managed services are essential for quality-demanding traffic, especially in large-scale IP networks where the aggregation of flows and the variety of traffic types are extensive. Although individual mechanisms have been widely investigated, not much related work exists on integrated approaches to QoS provisioning that are also feasible to implement. This work presents a thorough approach to the design, dimensioning and provisioning of a high priority service for high-quality demanding traffic over an IP network. Our approach employs efficient scheduling and a dynamic admission control scheme while demonstrating novel characteristics in terms of the quality offered to IP flows.

In this paper we present an efficient scheme for the multicast transmission of the data in the Universal Mobile Telecommunications System (UMTS). We take advantage of the tree topology of the examined network and we introduce the use of Routing Lists (RLs) in the nodes of the UMTS. The adoption of these lists leads to the decrement of the transmitted packets and the efficient use of network resources during the multicast transmission of the data. We describe in detail the necessary steps for the successful multicast transfer of data. Furthermore, we analyze the handling of special cases such as user mobility scenarios. Especially, the various handover types are examined along with the Serving Radio Network Subsystem (SRNS) relocation procedure.

It is known that multicasting is an efficient method of supporting group communication as it allows the transmission of packets to multiple destinations using fewer network resources. Thus, service providers are increasingly interested in supporting multicast communications over wireless networks and in particular over UMTS. Multicasting is a more efficient method of supporting group communication than unicasting or broadcasting, as it allows transmission and routing of packets to multiple destinations using fewer network resources. In this paper the three above mentioned methods of supporting group communication are analyzed in terms of their performance

Abstract In this paper, we present a framework that integrates three‐dimensional (3D) mesh streaming and compression techniques and algorithms into our EVE‐II networked virtual environments (NVEs) platform, in order to offer support for large‐scale environments as well as highly complex world geometry. This framework allows the partial and progressive transmission of 3D worlds as well as of separate meshes, achieving reduced waiting times for the end‐user and improved network utilization. We also present a 3D mesh compression method focused on network communication, which is designed to support progressive mesh transmission, offering a fast and effective means of reducing the storage and transmission needs for geometrical data. This method is integrated in the above framework and utilizes prediction to achieve efficient lossy compression of 3D geometry. Copyright © 2006 John Wiley & Sons, Ltd.

In this paper, we present the design principles for virtual spaces and two different tools as solutions for supporting e-collaboration and multi-user communication in Web-based learning communities. The first solution, called Virtual Conference, is designed and implemented in the framework of the VirRAD European project. It is a two-dimensional space where participants represented by their photos can use various e-collaboration tools. The second solution, called EVE Training Area, is a three-dimensional space where participants, represented by 3D humanoid avatars, can use a variety of e-collaboration tools. This paper describes the functionality provided by both tools, compares them, and proposes cases for exploiting each solution.

In this paper the issue of the architectural organization of a bandwidth broker with respect to the distribution of functionalities among separate entities is examined. We discuss the benefits of a distributed versus a centralized architecture and study some of the most important implementations. We also present a novel design proposal that builds on our earlier work on the admission control module of a bandwidth broker and introduces it in the framework of a distributed bandwidth broker architecture. Our conclusions are supported by a series of simulated experiments that we analyze.

The implementation of successful assured forwarding (AF) services according to the DiffServ framework remains a challenging problem today, despite the numerous proposals for AF PHB mechanisms and AF-based service implementations. In this work, we propose two modules, the TCP-window aware marker (TWAM) and the dynamic WRED (DWRED) mechanism for implementing the DiffServ AF PHB. We provide analytical models and an experimental evaluation in order to demonstrate how they succeed in enhancing the quality, increasing fairness, improving the performance and easing the deployment of a production- level AF-based service.

This paper presents the current state of the art in Web3d multi-user technologies and more specifically networked virtual environment platforms that support the X3D standard, which are currently limited in number, and also the existing X3D browsers that enable these applications. Furthermore, this paper presents the architecture of a platform, called EVE, which was developed to support multi-user virtual environments and was initially based on VRML, as well as the implementation regarding the process of upgrading this platform in order to fully support the X3D standard, using the open-source Xj3D library. Finally, the benefits of shifting to the X3D standard are presented, and some of the problems that currently exist are discussed.

DiffServ is the basis of contemporary QoS-enabled networks. Setting up DiffServ QoS requires extensive engineering effort in dimensioning and provisioning, especially for adjacent networks under different administrations linked in a "federated" hierarchy. In this paper we present a case study for QoS techniques employed in the GRNET MAN networks of Athens and Crete. After introducing the supported QoS mechanisms and service types, we discuss our dimensioning methodology and present two algorithms for worst-case dimensioning. We explain the provisioning mechanisms of GRNET and we present in brief our new automated provisioning ANS tool. Finally, we deal with the extension of our mechanisms and tools in hierarchically federated networks and give some future directions of our work

UMTS is evolving toward a future wireless all-IP network. In this paper we present how it supports realtime IP multimedia services, as these services are expected to drive the adoption of wireless all-IP networks. The scheme of real time streaming video is one of the newcomers in wireless data communication and in particular in UMTS, raising a number of novel requirements in both telecommunication and data communication systems. This scheme applies when the mobile user is experiencing real time video content. In this work we focus on the design and implementation of a rate and loss control mechanism for monitoring the UMTS network state and estimating the appropriate rate of the streaming video data.

Wireless LANs (WLANs) have edged into numerous mobile and wireless users' daily experience worldwide as a mainstream connectivity solution for a broad range of applications. Even though WLANs offer very high channel bandwidth, they show long network-layer handoff latency. This is a restraining factor for mobile clients using interactive multimedia applications such as voice over IP (VoIP) or video streaming. The paper presents an 802.11-dependent fast IP handoff method which quickly restores IP connectivity for mobile clients running next generation WLAN applications such as voice over WLANs (VoWLAN). This method outperforms other existing proposed IP mobility solutions in 802.11 WLANs as verified from real performance testing, while introducing insignificant compulsory additions to the existing 802.11 wireless LAN framework.

OpenH323 is an open source H.323 implementation that has been ported to IPv6. In this paper we briefly introduce the library architecture and the performance criteria with which the ported version should be evaluated. We then present a variety of experiments that we conducted in order to comparatively evaluate the IPv4 and IPv6 protocol stacks. We also present the results of some initial experiments comparing IPv4 and IPv6 performance under congested network links and the conclusions that they lead us to.

This paper focuses on the performance monitoring of a networked virtual environment, called EVE, in order to identify the elements that degrade its network performance. In particular, based both on the architectural and communication model that EVE adopts in order to cope with the dynamic behavior of the network, we performed a series of experiments, taking into account the number of the connected users, the network load as well as the connection type of the users.

In this paper we present a Web-based tool that facilitates instructors and trainers to easily develop learning objects and online courses so as to serve their distant learners' needs. Additionally, we present the way content created using that tool can be delivered to the learners during a learning process. We therefore present a sample content management and delivery system that exploits the potential of the above-mentioned Web-based tool. The resultant e-learning content can be easily searched and retrieved, tracked in terms of the learners' interactions with it and reused within different learning objects and courses.

This work focuses on the operation of the bandwidth broker, an entity that is responsible for managing the bandwidth within a network domain and for the communication with bandwidth brokers of neighboring domains. A very important aspect of the bandwidth broker is its admission control module that determines whether the bandwidth reservation requests are going to be accepted or not. We summarize the status of the current research in this field and propose architecture for the admission control module that aims at achieving a satisfactory balance between maximizing the resource utilization for the network provider and minimizing the overhead of the module. This is achieved by gathering and examining sets of book-ahead requests and by adapting the size of the set to be examined so that the network utilization and the computation overhead are appropriately balanced.

The increased need for quality of service (QoS) in today's networks has concentrated a lot of research and implementation efforts. Particular interest exists for the exploitation of the DiffServ framework towards the provision of qualitative services in MAN and WAN worldwide. Although individual mechanisms have been widely investigated, not many references to studies combining all levels of priority and QoS provisioning exist. This work aims at presenting a thorough and unified approach to the dimensioning and provisioning of a high priority service for high-quality demanding traffic over a MAN/WAN environment. Our approach anticipates for bounds in specific quality metrics and is demonstrated by the experimental case-study of a high-priority service over a MAN topology.

This paper describes a solution to extend the managed bandwidth service (MBS), which is provided on a backbone network using MPLS VPN, to non-MPLS domains and also evaluates it. It is based on the class based weighted fair queuing mechanism (CBWFQ) and describes the way it should be implemented to provide guaranteed bandwidth connections. In particular, CBWFQ can provide assured bandwidth connections when simultaneously leads to efficient bandwidth utilization. In addition, the proposed solution is being tested on simulation environment (using the network simulator) in order to evaluate its performance characteristics. On the simulation tests had been reserved specific amount of bandwidth for specific flows and their throughput was measured in order to understand if the proposed solution works well. Finally, the results are very well and prove that this method can guarantee bandwidth for every flow in all network conditions (congested or uncongested). At last, the paper presents a technical example of router configuration for implementing the MBS service according to the basic proposed solution.

We discuss the development of virtual communities and especially e-learning communities. In particular, we are inspired by VirRAD European project, and we present the intermediate results that have raised from the definition of this virtual radiopharmacy community.

A lot of research work has recently focused on the exploitation of the DiffServ framework towards building reliable networking services that provide deterministic quality guarantees. In this work we are attempting to devise a DiffServ-based service model for relative differentiation of traffic in a network serving aggregated traffic. The service model proposed aims at providing a minimum capacity during congestion and a bounded average end-to-end delay to profile-conforming traffic, obtaining thus a relatively better performance when compared to the best-effort service. We provide the framework on which the proposed service model is based and we present results from its deployment in a simulation environment.

The growing need for communication, visualization and organization technologies in the field of e-learning environments has led to the application of virtual reality and the use of collaborative virtual environments. The paper presents a system architecture to support such environments, defined by user needs and using state of the art technologies.

Shared or networked virtual environments are one of the most promising uses of the virtual reality technology. While a lot of research has been done in the area of multi-user virtual environments corresponding to the sharing of events very few research has been done on specific services and functionality. However both the requirements and the kind of the offered services affect significantly the design of a system. In this paper we present the main issues in the design of a platform to support the distant education process using networked virtual environments. We also introduce the term Educational Virtual Environments and their basic requirements. According to these requirements of the educational virtual environments we propose both a suitable architecture and a protocol for the interaction between the components of this architecture.

The use of Internet services has become part of everyday life. The need for more advanced applications is increasing and solutions have to be provided in order to meet it. Multimedia information is becoming more popular. The connection bandwidth is not yet ready to cope with rising expectations for applications such as video on demand (VoD). We propose a way to implement such a service over a limited bandwidth/best effort Internet based network. Our proposal consists of the implementation of algorithms and the introduction of quality of service features on a network such as the Internet that inherently does not support such features. We propose two techniques for the implementation of an Internet based video on demand service. The first deals with the distribution of video titles on several video servers and is called the Disk Manipulation Algorithm (DMA). The second gives a dynamic nature to the service, imposes a virtual routing procedure to the system and is called the Virtual Routing Algorithm (VRA).

The exceptional advent and dominance of interactive multimedia applications in our days has led to the need for their exploitation for educational, among many other, purposes. In this work, we present the design and implementation of a multimedia annotation environment for young children using the Java 2 Platform. This environment was developed to provide children of ages 4 to 8 with the opportunity to reflect upon and annotate episodes from their everyday life.

We present a unified approach for delivering hypermedia/multimedia objects over broadband networks. Documents are stored in various multimedia servers, while the inline data may reside in their own media servers, attached to the multimedia servers. The described service consists of several multimedia servers and a set of functions that intend to present to the end user interactive information in real time. Users interact with the service requesting multimedia documents on demand. Various media streams are transmitted over different parallel connections according to their transmission requirements. The hypermedia documents are structured using a hypermedia markup language that keeps information of the spatio temporal relationships among document's media components. In order to deal with the variant network behavior, buffering manipulation mechanisms and grading of the transmitted media quality techniques are proposed to smooth presentation and synchronization anomalies.

No abstract available.

Our work deals with the analysis of the queueing delays of buffered multistage Banyan networks of multiprocessors. We provide tight upper bounds on the mean delays of the second stage and beyond, in the case of infinite buffers. Our results are validated by simulations performed on a network simulator constructed by us. The analytic work for network stages beyond the first, provides a partial answer to open problems posed by previous research.