In this article we examine the architecture of an entity used for automatic management and provisioning of resources for DiffServ networks. We examine the existing literature and implementations in this area, focusing on the design choices made, and we propose an architecture for the design of Bandwidth Brokers that combines an adaptive admission control algorithm for increased utilization of network resources and a mechanism for reducing the complexity overhead that intends to be both simple and effective. Specifically, we present a novel 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. We complement our theoretical discussion with extensive experimental simulations for the proposed Bandwidth Broker components and analysis of the results. The simulations study the possible configurations of the proposed algorithm and also compare it with alternative admission control policies. Copyright © 2007 John Wiley & Sons, Ltd.

In this paper, we propose a novel architecture for the admission control module of a Bandwidth Broker entity that aims at achieving a satisfactory balance between maximizing the resource utilization for the managed network and minimizing the overhead of the module. We also describe, analyze and evaluate mechanisms which aim at solving the additional problems of fairly prioritizing resubmitted requests and efficiently handling requests which do not specify ending times. We use the well known network simulator ns-2, as well as a custom simulation environment in order to study the performance characteristics of the proposed mechanisms and compare them with various alternatives for the admission control module of a Bandwidth Broker. We provide the results of the experimental evaluations and the conclusions they lead us to for the relative importance of the proposed solution and the various alternatives, their advantages and drawbacks, and the environments for which each one is best suited.

In this paper we present various tele-teaching scenarios over ATM network infrastructure. In each scenario we present the standards which we use, the logical components, the demand in resources (network resources and equipment) and its special characteristics. Main result of our experiments is that broadband networks offer many capabilities for high quality Teleteaching and generally speaking high quality Telematic services.

It is well known that both space and the spatial organization play an important role in our work and learning environments as well as in everyday life. There is a definite need for many persons to design their space along with an expert and to preview it in order to test its functionality. Many times there is a need for the inhabitants and workers to collaborate in order to co-design their space from distance. Multi-user 3D virtual environments are a powerful form of collaborative telecommunication applications, enabling the users to share a common three dimensional space and interact with each other as well as with the environment surrounding them, in order to collaboratively solve problems or aid learning processes. This paper presents the work done for extending a multi-user virtual environments platform, to support collaborative spatial design applications. Furthermore, a usage scenario is presented concerning the collaborative design of a classroom for educational purposes.

This paper presents the design, implementation and evaluation of EVE Community Prototype, which is an educational virtual community aiming to meet the requirements of a Virtual Collaboration Space and to support e-learning services. Furthermore, this paper describes the design and implementation of an integrated platform for Networked Virtual Environments, called EVE Platform, which supports the afore-mentioned educational community. This platform supports stable event sharing and creation of multi-user three dimensional (3D) places, H.323-based voice over IP services integrated in 3D spaces as well as multiple concurrent virtual worlds.

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.

This paper is a summary of our experiences on a case study for porting applications to IPv6. We present the results of the effort to port OpenH323, an open-source H.323 platform to IPv6, which we believe can serve as guidelines for other projects with similar goals. We briefly present the structure of the OpenH323 platform. We also discuss a number of issues arising during the porting of a platform to IPv6, like which would be the easiest approach to the porting procedure, how compatibility with earlier, IPv4-only versions of the platform could be retained, if there are any useful tools for assisting this task, how and when one could be positive that the necessary modifications had been made, and which testing procedures should be followed. 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. Copyright © 2005 John Wiley & Sons, Ltd.

This paper describes the design and implementation of the ASP-NG system. The main modules of the ASP-NG system are the AoD service and the Web Portal. The ASP-NG Portal is a portal for providing the user with the necessary interface in order to access an Application on Demand (AoD) service. The ASP-NG portal is responsible for the interaction with the user of the AoD service. Using the AoD service the user rents an application for a limited time period at a fraction of the actual cost of the application. The AoD service is responsible for downloading the appropriate parts of the application according to the user's actions, while enforcing the mutually agreed frame between the user and the Application Service Provider (ASP). The implementation of the ASP-NG portal is based on the Web Services of the Java 2, Enterprise Edition platform and the implementation of the AoD module is based on C + + programming language. The ASP-NG portal offers to its users the capability to select and customize the language of the user interface in order to present information in their preferred language. Moreover the ASP-NG portal offers to the portal administrator the capability to customise the look and feel of the ASP-NG portal.

In this paper, we present the design and implementation of an integrated platform for Networked Virtual Environments. This platform called EVE-II is an enhancement of the EVE distributed virtual reality platform, supporting stable event sharing for multi-user 3D places, easy creation of 3D multi-user3D places, H.323-based Voice over IP services integrated in a 3D spaces well as many concurrent 3D multi-user spaces.

A “one multicast stream” mechanism is a mechanism, which can be used for multicast multimedia data with the use of one multicast stream over heterogeneous networks, like the Internet, and has the capability to adapt the transmission of the multimedia data to network changes. In this paper, we describe a “one multicast stream” mechanism for adaptive transmission of multimedia data, which is based on real time protocols. In addition, the proposed mechanism uses an inter-receiver fairness function in order to treat the group of receivers with fairness in a heterogeneous environment. We evaluate the adaptive multicast transmission mechanism through a number of simulations and compare it with a number of similar schemes available to the literature (LBA+, TFMCC,

This paper describes the design and the implementation of the ASP-NG portal, which is a portal for providing the user with the necessary interface in order to access an Application on Demand (AoD) service. The ASP-NG portal is responsible for the interaction with the user of the Application on Demand service. The implementation of the ASP-NG portal is based on the Java 2, Enterprise Edition (J2EE) platform. The ASP-NG portal offers to its users the capability to select and customize the language of the user interface in order to present information in their preferred language. Moreover the ASP-NG portal offers to the portal administrator the capability to customize the look and feel of the ASPNG portal.

This paper describes a Quality of Service (QoS) service on an IPv6 domain that aims to service aggregates of real-time traffic with minimum delay, jitter, and packet loss. It contains results from the tests that were performed in order to configure and evaluate the QoS mechanisms. As an actual example of real-time traffic, we have used the OpenH323 project, an open source H.323 implementation that has been ported to IPv6. The QoS mechanisms in IPv6 networks is still a field that has not been researched adequately, and we therefore present the results from the experiments in our IPv6 network that took advantage of the QoS mechanisms. This QoS service uses the Modular QoS CLI (MQC) mechanism and especially the Low Latency Queue feature (LLQ) in order to treat packets from real-time applications.

In this paper, we present the design and implementation of a VRML97 multi-user layer, which is introduced in the EVE distributed virtual reality platform. Main consideration of our multi-user extension is the ease of transforming single-user virtual worlds to multi-user virtual worlds, as well as the conformity with any standard VRML97 browser. Furthermore, we present the EVE'scommunication platform, which can be used in order to support Collaborative Virtual Environments (CVEs). Main issues regarding the effective network communication as well as the initialization of the 3D scene are discussed in this paper.

We discuss our experience form porting the OpenH323 platform to IPv6. We briefly discuss the structure of the platform, and we present the various problems we faced and choices we made, regarding the easiest approach to the porting procedure, the compatibility with earlier, IPv4-only versions of the platform, the existence of tools that could aid us with the porting task and the verification of results. We believe that the results of our effort can serve as guidelines for other similar projects and we present a general methodology which might be applicable to similar porting projects.

An Educational Virtual Environment (EVE) is an instance of a Collaborative Virtual Environment (CVE), which focalises in providing collaborative, as well as educational, functionalities, such as synchronous and asynchronous e-learning services. This paper describes such an educational virtual community, which aims to meet the requirements of a virtual collaboration space and furthermore to support e-learning services. In particular, we are developing a Web-based system, which allows users to communicate with the other members of the community through forums, chat, e-mail, to schedule events which take place in the learning environment and to join, and even create, courses, which are held in 3D multi-user worlds where users are represented by avatars. These characteristics offer extended functionalities such as support of application sharing and voice chat, transmission of the educational material as well as transmission of the users' profiles to the other community members. We describe the model of this community and the functionalities that it provides.

The collaborative virtual environments have become a good media for supporting collaborative e-learning services. In this paper we present the Educational Virtual Environments (EVE) platform, which integrates a variety of communication a collaboration tools to support collaborative virtual environments focused on collaborative e-learning.