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This work describes extensions to the well-known Distributed Coordination Function (DCF) model to account for IEEE802.11n point-to-point links. The developed extensions cover adaptions to the throughput and delay estimation for this type of link as well peculiarities of hardware and implementations within the Linux Kernel. Instead of using simulations, the approach was extensively verified on real-world deployments at various link distances. Additionally, trials were conducted to optimize the CWmin values and the number of retries to maximize throughput and minimize delay. The results of this work can be used to estimate the properties of long-distance 802.11 links beforehand, allowing the network to be planned more accurately.
SDN and WMN evolved to be sophisticated technologies used in a variety of applications. However, a combined approach called wmSDN has not been widely addressed in the research community. Our idea in this field consists of WiFi-based point-to-point links managed by the OpenFlow protocol. We investigate two different issues regarding this idea. First, which WiFi operational mode is suitable in an OpenFlow managed broadcast domain? Second, does the performance decrease compared with other routing or switching principles? Therefore, we set up a real-world testbed and a suitable simulation environment. Unlike previous work, we show that it is possible to use WiFi links without conducting MAC address rewriting at each hop by utilizing the 4-address-mode.
The MoMoSat service will enable mobile end-users to view, manage, annotate, and communicate mapbased information in the field. The handled information exists of a huge volume of raster (satellite or aerial images) and vector data (i.e. street networks, cadastral maps or points of interest), as well as text-specific geo-referenced textual notes (the so-called 'GeoNotes') and real-time voice.
Mobile Datenkommunikation basiert üblicherweise auf der drahtlosen Anbindung eines Endgerätes an eine Basisstation, die ihrerseits an eine feste Infrastruktur angebunden ist. In vielen Szenarien sind diese Voraussetzungen jedoch nicht gegeben. Beispiele hierfür sind Katastrophen wie Hochwasser, Erdbeben oder Flugzeugabstürze in dünn besiedelten Regionen. Einen Lösungsansatz für sich daraus ergebende Anforderungen bieten dynamisch aufgebaute Ad-Hoc Netze mit einer satellitengestützten Anbindung an eine Festnetz-Infrastruktur. In solchen Netzen stellen die mobilen Terminals die benötigte lokale Infrastruktur selbst dynamisch her. Ziel der hier vorgestellten Arbeiten ist es, die Zuverlässigkeit und Dienstqualität der verwendeten Technologien zu untersuchen und durch geeignete Mechanismen so anzupassen, dass die Anforderungen typischer Applikationen möglichst erfüllt werden. Zur Demonstration wurde ein Prototyp aufgebaut, der unter anderem die Anwendungen "Voice over IP" (VoIP), "Datenbankzugriff im Intranet" und "Internetzugang" (WWW) untersucht.