FOKUS Publikationen 2003 - 2005

Common intended access to a physically unshareable resource requires arbitration. Since in wireless communications the transmission medium cannot be shared without loss of information, medium access control (MAC) plays the role of an arbiter stipulating, for each of the intended users, the conditions and parameters of exclusive access rights. The major challenge in designing a good MAC protocol is to provide each user with the negotiated quality-of-service (QoS) parameters while, at the same time, utilizing the network resources as efficiently as possible. Thus, an ideal MAC protocol must strike a balance between the conflicting goals of QoS provisioning, efficiency, simplicity, and service controllability. The MAC protocol improvements ensure a dominant effect on the develop ment of the QoS and other future breakthrough wireless technologies.

Software and system assurance is a growing concern. A look at some of the domains involved, including at least medical devices, automotive, railway, aeronautical, space and telecommunications provides a feeling on the importance of the topic. For many of these domains, and partly because of the increasing complexity of software, validation is an open issue and not straightforward at all, both from a technical and from a managerial point of view. Another topic to consider is that validation is often performed at the end the development lifecycle, which results in obvious calendar problems. One of the consequences is that the relevance of lifecycle processes such as system testing and validation must be broadened. Therefore inputs from research and experience from industry is required in order to enable innovative, and often more rigorous, approaches.

The main contribution of this chapter is a novel paradigm for future mcommerce multimedia communications and applications that can be integrated with other multifunctional multimedia e-applications (e.g., e-learning, ehealth, e-culture, e-work, etc.) in a cost-effective manner. We also propose an implementation of this paradigm based on our novel QoS-oriented medium access control (MAC) technology and the fully distributed all-IP/ ATM architecture. The proposed QoS-oriented MAC technology, along with the all-IP/ATM architecture, will provide cost-effective broadband communication multiservice for mobile and geographically distributed users anytime and anywhere.

Future broadband satellite networks for multimedia will be seamlessly integrated into terrestrial broadband networks which often use ATM (Asynchronous Transfer Mode) and recently also the less complex MPLS (Multi Protocol Label Switching) technique as transmission and switching protocol. In light of this, future broadband satellite networks may adopt the ATM transmission scheme and implement ATM or ATM-like switches on board the satellites. However, as compared to communication in fixed networks, satellite communication is characterised by special constraints (e.g. signal delay, channel quality, dynamic network topology) that require novel ATM-based communication technology for satellite systems. This paper presents results from the ATM-Sat project that aims to complete this technically c hallenging and important R&D task in the cooperation between DLR, Fraunhofer Gesellschaft and Tesat-Spacecom. In brief the following aspects have been addressed in the ATM-Sat project: - development of the concept and communication technology for a multimedia satellite system with: - NGSO (Non-GeoStationary Orbit) satellites; - ISLs (Inter Satellite Links); - on-board ATM switching; - fixed and mobile terminals - verification of the developed communication technology with a demonstrator In particular the ATM-Sat R&D tasks cover the system and protocol architecture, on-board processing, ISL routing, up/downlink and on board ATM resource management (including medium access control), error control, IP over satellite-ATM, and active intelligent antennas.

Satellite transmissions have an important role in telephone ommunications, television broadcasting, computer communications, maritime navigation, and military command and control.Moreover, in many situations they may be the only possible communication set-up. Trends in telecommunications indicate that four major growth market/service areas are messaging and navigation services (wireless and satellite), mobility services (wireless and satellite), video delivery services (cable and satellite), and interactive multimedia services (fiber/cable, satellite). When using geostationary satellites (GEO), the long propagation delay may have great impact, given the end-to-end delay userâs requirements of relevant applications; moreover, atmospheric conditions may seriously affect data transmission . Since satellite bandwidth is a relatively scarce resource compared to the terrestrial one (e.g., in optical transport networks), and the environment is harsher, resource management of the radio segment plays an important role in the systemâs efficiency and economy. The radio resource management (RMM) entity is responsible for the utilization of the air interface resources, and covers power control, handover, admission control, congestion control, bandwidth allocation, and packet scheduling. RRM functions are crucial for the best possible utilization of the capacity. RRM functions can be implemented in different ways, thus having an impact on the overall system efficiency. This tutorial aims to provide an overview of satellite transmission aspects at various OSI layers, with emphasis o n the MAC layer; some cross-layer solutions for bandwidth allocation are also indicated. Far from being an exhaustive survey (mainly due to the extensive nature of the subject), it offers the readers an extensive bibliography, which could be used for further research on specific aspects.

Satellite transmissions have an important role in telephone communications, television broadcasting, computer communications, maritime navigation, and military command and control. Moreover, in many situations they may be the only possible communication set-up. Trends in telecommunications indicate that four major growth market/service areas are messaging and navigation services (wireless and satellite), mobility services (wireless and satellite), video delivery services (cable and satellite), and interactive multimedia services (fibre/cable, satellite). When using geostationary satellites (GEO), the long propagation delay may have great impact, given the end-to-end delay userâs requirements of relevant applications; moreover, atmospheric conditions may seriously affect data tran smission. Since satellite bandwidth is a relatively scarce resource compared to the terrestrial one (e.g. in optical transport networks), and the environment is harsher, resource management of the radio segment plays an important role in the systemâs efficiency and economy. The radio resource management (RMM) entity is responsible for the utilization of the air interface resources, and covers power control, handover, admission control, congestion control, bandwidth allocation, and packet scheduling. RRM functions are crucial for the best possible utilization of the capacity. RRM functions can be implemented in different ways, thus having an impact on the overall system efficiency. This tutorial aims to provide an overview of satellite transmission aspects at various OSI layers, wi th emphasis on the MAC layer; some cross-layer solutions for bandwidth allocation are also indicated. Far from being an exhaustive survey (mainly due to the extensive nature of the subject), it offers the readers an extensive bibliography, which could be used for further research on specific aspects

Over the last few years, novel architectures like ad-hoc and sensor networks have introduced new challenges in the way the communication infrastructure must be addressed. Unlike traditional approaches, these architectures require the complete self-organization of nodes as well as the support of mobility. A common problem encountered in such networks is the fundamental requirement of guaranteeing the connectivity between nodes. A number of network functionality have then to be reassessed, where two components must receive particular attention: topology control and node localization. In this paper, we survey the current state of the art for these domains and identify some open issues for future research and development.

Verteilte Systeme finden sich häufig in sicherheitskritischen Bereichen wie Flugsicherung, Telekommunikation oder Verteidigung. Das EU-Forschungsprojekt COACH entwickelt für CORBA und CCM eine neue speziell auf solche Anwendungen zugeschnittene Sicherheitsarchitektur.

Multimedia data play an essential role in today's mobile commerce applications. Indeed, a large array of e-commerce and mobile commerce applications rely directly or indirectly on multimedia data, ranging from simple news lines, to sophisticated on-line sales catalogs, to virtual show rooms. They are placing new demands on stringent Quality of Service (QoS) requirements in terms of bandwidth, delay and loss of messages. It is apparent that terrestrial networks alone cannot meet this growing demand. Consequently, it is natural to contemplate integrated solutions involving a combination of satellite and terrestrial networks.

Low earth orbit (LEO) satellite systems gained considerable interest in the past decade and were expected to be instrumental in future telecommunications systems. Nevertheless, the first two LEO satellite networks that are currently in operation have not come to fruition on account of the limited spectrum of services that they provide. In this context, future LEO satellite networks will be geared towards the provision of multimedia services. In this paper a novel call admission control and inter-satellite handover management scheme tailored for multimedia LEO satellite systems is proposed and evaluated. In addition, the proposed scheme is examined in satellite diversity based systems and two different satellite selection criteria, which can be applied to both new and handover requests, are assessed.

Traditionally the testing and test control notation TTCN has been used and accepted widely in the telecom industry. The new version TTCN-3 is intended to be applicable to a broader scope of communication and software systems. This paper describes the initial results of a research project with the aim of evaluating the use of TTCN-3 within the automative telematics domain. The paper addresses the use of TTCN-3 to specify the reusable test cases for the telematics domain, the development of a TTCN-3 test platform for telematics systems and future work required before the requirements of the industrial testing processes within the automotive industry can be met.

Growth of processor and networking technologies are enabling to connect real-world and computer systems through devices and much attention is being paid to the context-aware services. One of the issues to provide services using ubiquitous or pervasive computing is how to connect heterogeneous hardware device and software component to provide services. This paper proposes a new object model named super distributed objects (SDO) for unified management of them. This model has been proposed to OMG1 and it is adopted by standardization in progress.

For the development of collaborative multimedia systems two tasks need to be done often. The multimedia connection between distributed systems has to be established and the information about the currently available resources has to be gathered to adapt the application to the environment. We present solutions for these two tasks. The integration of these two solutions became part of a CORBA Component Model (CCM) based middleware and will therefore greatly reduce the development effort of such systems.