Virtual Collaboration Spaces: The EVE Community

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

Building Educational Virtual Environments

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

Performance Analysis of Adaptive Admission Control Algorithms for Bandwidth Brokers

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. KEY WORDS: Bandwidth broker; admission control; DiffServ; adaptive; SLA. 1

Multimedia transmission with adaptive QoS based on real-time protocols

this paper, we describe a mechanism for adaptive transmission of multimedia data, which is based on real-time protocols. The proposed mechanism can be used for unicast or multicast transmission of multimedia data over heterogeneous networks, like the Internet, and has the capability to adapt the transmission of the multimedia data to network changes. In addition, the implemented mechanism uses an inter-receiver fairness function in order to treat the group of clients with fairness during the multicast transmission in a heterogeneous environment. The proposed mechanism uses a `friendly' to the network users congestion control policy to control the transmission of the multimedia data. We implement a prototype application based on the proposed mechanism and we evaluate the proposed mechanism both in unicast and multicast transmission through a number of experiment and a number of simulations in order to examine its fairness to a group of clients and its behaviour against transport protocols (TCP) and UDP data streams. Copyright # 2003 John Wiley & Sons, Lt