Vaggelis Kapoulas

Performance evaluation of routing protocols for multimedia transmission over mobile ad hoc networks

Mobile ad hoc networks (MANETs) are becoming more essential to wireless communications due to growing popularity of mobile devices. The integration of mobile ad hoc devices inside vehicles has led to another type of networks, called Vehicular Ad hoc Networks (VANETs) which are also becoming important. These networks require specialized routing protocols due to their ad hoc nature. The performance of these protocols has been tested for the case of general traffic but not in respect with to multimedia traffic and especially video transmission. In this paper we conduct a number of simulations in order to evaluate the performance of three of the most popular routing protocols for MANETs and VANETs, namely AODV, DSR and OLSR, for different number of simultaneous video transmissions. We use the packet delivery ratio, the end-to-end delay, the packet delay variation (jitter) and the routing overhead as evaluation metrics. The results indicate that the DSR protocol outperforms AODV and OLSR in terms of end-to-end delay and packet delay variation and seems to be the most efficient routing protocol when multimedia traffic and especially video traffic is considered.

Virtual European School-VES

The Virtual European School (VES) is an ongoing European project-funded by the Educational Multimedia Task Force initiative of the European Union-with the aim to develop a comprehensive online resource of teaching material for secondary school education. The system will be fed by a group of smaller publishing houses from different European countries (Austria, Italy, Greece, Great Britain) specialising in educational material. The offer will contain multimedia material, CBT products, and also additional background materials, such as passages from schoolbooks, or Internet resources. The technical structure of the VES system will be based on Internet technologies, with interconnected VES servers in each participating region. The multimedia material will be stored in a database, with multilingual annotations for each project. There exist three user groups within the VES: publishers, teachers and pupils.

A web-based virtual community

This paper describes functionality and architectural issues in the design of a web-based virtual community. This virtual community aims to meet the requirements of a virtual collaboration system with both autonomous and collaborative e-learning services, by supporting communities whose members interact and form groups based on their common interests.

Using VR technology to support e-learning: the 3D virtual radiopharmacy laboratory

We present a virtual laboratory, which is designed and implemented in the framework of the VirRAD European project. This laboratory represents a 3D simulation of a radio-pharmacy laboratory, where learners, represented by 3D avatars, can experiment on radio-pharmacy equipment by carrying out specific learning scenarios. We describe the functionality provided by this laboratory, the motivation factors which led to its formation, the technological decisions that were made for the optimization of the system as well as the envisioned steps to be carried out.

A GPSR Enhancement Mechanism for Routing in VANETs

Vehicular Ad Hoc Networks (VANETs) are considered as a special case of mobile Ad Hoc Networks (MANETs) and are recently gaining a great attention from the research community. The need for improved road safety, traffic efficiency and direct communication along with the great complexity in routing, makes VANETs a highly challenging field. Routing in VANETs has to adapt to special characteristics such as high speed and road pattern movement as well as high linkage break probability. In this paper, we propose an enhancement mechanism for the GPSR routing protocol and present its performance for urban and highway scenarios. Its performance is compared to the performance of the most common MANET routing protocols adopted in VANETs. The proposed enhancement is shown to be beneficial in most occasions as it outperforms the rest of the tested routing protocols.

Extending QoS support from Layer 3 to Layer 2

This paper presents some of the results obtained by the application of Ethernet layer 2 quality of service in IP networks. IP networks traditionally provide quality of service in Layer 3. However, since there is an enormous existing Layer 2 infrastructure, todaypsilas networks could benefit from the deployment of Layer 2 quality of service and the cooperation between layer 2 quality of service and layer 3 quality of service. In this paper, experiments are suggested and conducted and a scheme is suggested for efficient cooperation between Layer 2 and Layer 3 QoS provisioning.

Deployment of broadband infrastructure in the region of Western Greece

This paper presents the work that is taking place in the Region of Western Greece in order to develop state-of-the-art broadband infrastructure. The current status of broadband infrastructure in the region is being analyzed and the main principles on which the deployment of the networks will be based on is being described, by presenting the metropolitan area networks and the wireless access networks that will be developed. Two case studies of such municipal networks are also presented in this paper

Cross Layer Design for Video Streaming in MANETs

Mobile Ad hoc NETworks (MANETs) are becoming more essential to wireless communications due to growing popularity of mobile devices. However, MANETs do not seem to effectively support multimedia applications and especially video transmission. In this work, we propose a cross-layer design that aims to improve the performance of video transmission using TCP Friendly Rate Control (TFRC). Our design provides priority to video packets and exploits information from the MAC layer in order to improve TFRCs performance. The proposed cross-layer design utilizes SNR measurements along the routing path, in order to make the route reconstruction procedure more efficient. Simulation results show that both the use of traffic classification and the SNR utilization lead to important improvements in terms of end-to-end Quality of Service (QoS).

A dynamic distributed video on demand service

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).

On-demand hypermedia/multimedia service over broadband networks

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 documents 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.