Volume 32, Issue 4

ABSTRACT Multi-hop wireless networks are in the focus of research since more than two decades. Mobile ad-hoc networks, wireless sensor networks, and wireless mesh networks are among the most prominent ones. The research in this area is done most often based on simulation studies. As these networks are hard to model with all their properties and operating system interdependencies, testbeds are an important alternative that has regained attention in largescale national and international research projects. In this paper we review architectures for next generation wireless networks including the aforementioned ones according to future applications. We introduce the DES-Testbed at the Freie Universität Berlin , which we believe is suitable to study these architectures or network configurations , as we call them. Furthermore, we discuss an approach on how to set up network configurations and perform long-term experiments.

ABSTRACT In wireless multihop networks, nodes cooperate to forward data packets. After years of simulation-based research, the next step is the evaluation of this paradigm under real-world conditions. However, due to the distributed nature of such a network in combination with the complex effects of electromagnetic wave propagation, it is extremely difficult to perform these experiments systematically. In this paper, we introduce a bundle of techniques and tools to tackle the fundamental problems of the control and analysis of such experiments.

ABSTRACT Cellular phones extend the traditional view on sensor and ad-hoc networks by allowing global communication through cellular infrastructure in addition to local ad-hoc communication. We exploit this mediation characteristic of cellular phones in a participatory sensor network supporting the search for mobile objects that can be sensed in the vicinity of cellphones but have no communication facilities. Our proposal improves upon existing geographic routing algorithms by using scoped flooding in order to take into account real-world constraints such as infrequent sensing with limited sensing ranges. We further make selective use of cellular communication to avoid the delay it takes to traverse long multi-hop routes. As we show, a well designed system reduces search delay and at the same time lowers cost in terms of energy spent for cellular and ad-hoc communication.

ABSTRACT Reliability is one of the key requirements for inter-vehicle communication in order to improve safety in road traffic. This paper describes the difficulties of inter-vehicle communication. We focus on an analysis of the state-of-the art MAC protocol draft IEEE P802.11p and its limitations in high load situations. For our analysis we consider a particular safety scenario: An emergency vehicle is approaching a traffic jam. In a simulation experiment, we highlight that severe packet loss can occur. The reliable transmission range can be reduced by up to 90%. The main reason for this degradation is interference caused by transmissions of other vehicles within the traffic jam. In the study, we focus on the vehicle at the very end of the traffic jam. There, we measure the number of packets per second that are successfully received from the emergency vehicle. The key observation is that only a small fraction of the warning lead time remains which will also reduce the time for the driver to react on this information on an approaching emergency vehicle.

ABSTRACT Wireless Mesh Networks (WMNs) are a good alternative to traditional wired access networks. However, emerging applications such as voice or video over IP make high demands on WMNs. A small change of the Quality-of-Service (QoS) metrics like packet loss, delay, and jitter have a significant impact on the Quality-of-Experience (QoE), a subjective measure from the user perspective. In this paper, we present a measurement-based dynamic bandwidth control mechanism for IEEE 802.11 mesh networks. The mechanism regulates the bandwidth of best effort traffic flows according to the QoE of real time services. The results show that the QoE for real time services can be guaranteed without complete best effort flow starvation.

ZUSAMMENFASSUNG Dieser Artikel richtet sich an die Verwaltungsspitzen der Fachhochschulen und geht der Frage nach, inwiefern Groupware in den Fachhochschulverwaltungen eingesetzt wird. Dazu wurde eine Umfrage unter 40 Fachhochschulen ausgewertet. Die Analyse belegt, dass Groupware — über die E- Mail-Funktion hinaus — in der Mehrheit der befragten Fachhochschulen bisher nicht eingesetzt wird. Wo sie jedoch eingesetzt wird, werden fortgeschrittene Funktionen wie z.B. gemeinsame Adressen- und Dokumentenverwaltungen und Workflowanwendungen nur in geringem Umfang genutzt. Viele Fachhochschulverwaltungen drohen hinsichtlich der Bewältigung anstehender Aufgaben im Morast schwerfälliger Verwaltungsprozesse und langsamer Kommunikation zu versinken. Verstärkt wird dieser Trend oft durch geringer werdende Haushaltsmittel, Personalausstattung sowie die steigenden Anforderungen durch die sich wandelnde Hochschullandschaft.