Abstract. The aim of the work is to analyse capabilities and limitations of different IEEE 802.11 technologies (IEEE 802.11 b/g/n), utilized for both multicast and unicast video streaming transmissions directed to mobile devices. Our preliminary research showed that results obtained with currently popular simulation tools can be drastically different than these possible in real-world environment, so, in order to correctly evaluate performance of video streaming, a simple wireless test-bed infrastructure has been created. The results show a strong dependence of the quality of video streaming on the chosen transmission technology. At the same time there are significant differences in perception quality between multicast (1:n) and unicast (1:1) streams, and also between devices offered by different manufacturers. The overall results seem to demonstrate, that, while multicast support quality in different products is still varied and often requires additional configuration, it is possible to select a WiFi access point model and determine the best system parameters to ensure a good video transfer conditions in terms of acceptable QoP/E (Quality of Perception/Exellence).

The development of broadband network access technologies available to users on land has triggered a rapid expansion of a diverse range of services provided by terrestrial networks. However, due to limitations of digital communication technologies in the off-shore area, the maritime ICT systems evolution so far has not followed that trend. Despite the e-navigation initiative defining the set of Maritime Services, the progress in the maritime ICT systems evolution has been slow. Only a few systems, including the VHF Data Exchange System (VDES), or the TRI-Media Telematic Oceanographic Network (TRITON) have been proposed to extend the basic set of services offered by classical radio-communication solutions. However, all those systems have significant limitations. The purpose of this paper is to introduce the netBaltic system designed as a fully heterogeneous system for modern maritime communications. Its unique feature is the capability to transparently use different communication technologies to efficiently support maritime ICT services, as well as openness for the incorporation of future communication technologies. The paper presents an overview of VDES, TRITON and netBaltic systems and analysis showing their expected strengths and weaknesses. The systems are then compared in simulated environments, illustrating real-world usage scenarios based on real maritime traffic information and performance measurements obtained during off-shore measurement campaigns. Results indicate that netBaltic seems to be the most versatile one and is capable of offering access to all services defined by International Maritime Organization, due to its ability to use different communication technologies simultaneously and functionality offered by its Delay Tolerant Networking component.

No abstract

No abstract

In this paper we propose a novel e-learning system, dedicated strictly to knowledge assessment tasks. In its functioning it utilizes web-based technologies, but its design differs radically from currently popular e-learning solutions which rely mostly on thin-client architecture. Our research proved that such architecture, while well suited for didactic content distribution systems is ill-suited for knowledge assessment products. In our design we employed loosely-tied distributed system architecture, strict modularity, test and simulation-based knowledge and skill assessment and an our original communications package called Communication Abstraction Layer (ComAL), specifically designed to support communication functions of elearning systems in diverse network conditions (including offline environment). The system was tested in production environment on Faculty of Electronics, Telecommunications and Informatics, Technical University of Gdansk with great success, reducing staff workload and increasing efficiency of didactic process. Tests also showed system's versatility as the system was deployed in environments of classroom, remote and blended learning.