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News on demand
(1996)
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.
Quantifying Interference in WiLD Networks using Topography Data and Realistic Antenna Patterns
(2019)
Avoiding possible interference is a key aspect to maximize the performance in Wi-Fi based Long Distance networks. In this paper we quantify self-induced interference based on data derived from our testbed and match the findings against simulations. By enhancing current simulation models with two key elements we significantly reduce the deviation between testbed and simulation: the usage of detailed antenna patterns compared to the cone model and propagation modeling enhanced by license-free topography data. Based on the gathered data we discuss several possible optimization approaches such as physical separation of local radios, tuning the sensitivity of the transmitter and using centralized compared to distributed channel assignment algorithms. While our testbed is based on 5 GHz Wi-Fi, we briefly discuss the possible impact of our results to other frequency bands.
WiFi-based Long Distance (WiLD) networks have emerged as a promising alternative technology approach for providing Internet in rural areas. An important factor in network planning of these wireless networks is estimating the path loss. In this work, we present various propagation models we found suitable for point-to-point (P2P) operation in the WiFi frequency bands. We conducted outdoor experiments with commercial offthe- shelf (COTS) hardware in our testbed made of 7 different long-distance links ranging from 450 m to 10.3 km and a mobile measurement station. We found that for short links with omni-directional antennas ground-reflection is a measurable phenomenon. For longer links, we show that either FSPL or the Longley-Rice model provides accurate results for certain links. We conclude that a good site survey is needed to exclude influences not included in the propagation models.
The combination of Software-Defined Networking (SDN) and Wireless Mesh Network (WMN) is challenging due to the different natures of both concepts. SDN describes networks with homogeneous, static and centralized controlled topologies. In contrast, a WMN is characterized by a dynamic and distributed network control, and adds new challenges with respect to time-critical operation. However, SDN and WMN are both associated with decreasing the operational costs for communication networks which is especially beneficial for internet provisioning in rural areas. This work surveys the current status for Software-Defined Wireless Mesh Networking. Besides a general overview in the domain of wireless SDN, this work focuses especially on different identified aspects: representing and controlling wireless interfaces, control-plane connection and topology discovery, modulation and coding, routing and load-balancing and client handling. A complete overview of surveyed solutions, open issues and new research directions is provided with regard to each aspect.
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.
Quantifying the spectrum occupancy in an outdoor 5 GHz WiFi network with directional antennas
(2018)
WiFi-based Long Distance networks are seen as a promising alternative for bringing broadband connectivity to rural areas. A key factor for the profitability of these networks is using license free bands. This work quantifies the current spectrum occupancy in our testbed, which covers rural and urban areas alike. The data mining is conducted on the same WiFi card and in parallel with an operational network. The presented evaluations reveal tendencies for various aspects: occupancy compared to population density, occupancy fluctuations, (joint)-vacant channels, the mean channel vacant duration, different approaches to model/forecast occupancy, and correlations among related interfaces.
An Empirical Evaluation of the Received Signal Strength Indicator for fixed outdoor 802.11 links
(2015)
For the evaluation of the received signal strength indication (RSSI) a different methodology compared to previous publications is introduced in this paper by exploiting a spectral scan feature of recent Qualcomm Atheros WiFi NICs. This method is compared to driver reports and to an industrial grade spectrum analyzer. During the conducted outdoor experiments a decreased scattering of the RSSI compared to previous publications is observed. By applying well-known mathematical tests for normality it is possible to show that the RSSI does not follow a normal distribution in a line-of-sight outdoor environment. The evaluated spectral scan features offers additional possibilities to develop interference classifiers which is an important step for frequency allocation in long-distance 802.11 networks.
WiFi-based Long Distance (WiLD) networks have emerged as a promising alternative approach for Internet in rural areas. The main hardware components of these networks are commercial off-the-shelf WiFi radios and directional antennas. During our experiences with real-world WiLD networks, we encountered that interference among long-distance links is a major issue even with high gain directional antennas. In this work, we are providing an in-depth analysis of these interference effects by conducting simulations in ns-3. To closely match the real-world interference effects, we implemented a module to load radiation pattern of commonly used antennas. We analyze two different interference scenarios typically present as a part of larger networks. The results show that side-lobes of directional antennas significantly influence the throughput of long-distance WiFi links depending on the orientation. This work emphasizes that the usage of simple directional antenna models needs to be considered carefully.
WiFi-based Long Distance (WiLD) networks have emerged as a promising alternative approach for Internet in rural areas. However, the MAC layer, which is based on the IEEE802.11 standard, comprises contiguous stations in a cell and is spatially restricted to a few hundred meters at most. In this work, we summarize efforts by different researchers to use IEEE802.11 over long-distances. In addition, we introduce WiLDToken, our solution to optimizing the throughput and fairness and reducing the delay on WiLD links. Compared to previous alternative MAC layers protocols for WiLD, our focus is on optimizing a single link in a multi-radio multi-channel mesh. We implement our protocol in the ns-3 network simulator and show thatWiLDToken is superior to an adapted version of the Distributed Coordination Function (DCF) for different link distances. We find that the throughput on a single link is close to the physical data-rate without a major decrease over longer distances.
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.
With the rapid advances in multimedia content delivery technologies, there is an increasing challenge for efficient Quality of Service (QoS) based multicast transport in mobile Internet environment. This paper discusses architectural approach for provision of multicast services in heterogeneous mobile IPv6 environment using context transfer. Following issues of QoS based mobile multicast transport are addressed: - Application of context transfer between access routers for seamless handover of active multicast services; - Adaptation of multicast group management and routing designed for wired IPv6 infrastructures to heterogeneous mobile environment; - Candidate access router discovery and context aware user interfaces for optimised handover; - Reliable mobile multicast for content delivery supported by context transfer at access routers; - Distributed QoS management of multicast services in heterogeneous mobile environment. The work is part of the mobile architecture developed in the EU IST project DAIDALOS.
Reliable multicast transport services for content delivery in heterogeneous mobile environment
(2007)
For efficient deployment of new reliable multicast applications in heterogeneous mobile Internet environments, appropriate retransmission strategies are proposed. The focus is the minimization of the protocol overhead for reliable transport taking into account behaviour in mobile networks (oss and handover behaviour) and application requirements (such as carousel file transfer, one-to-many download and media streaming combined with recording). The proposed techniques are designed as building blocks for localized multicast error control supported by access routers. Considering IETF RMT standardization work, the discussed retransmission approaches can be used for flexible configuration of tree-based reliable multicast protocols in converged wired and wireless Internet environment. The implementation developed for the European project DAIDALOS [1] is based on Linux IPv6 environment. Simulations in ns2 focusing on the benefits of the proposed multicast retransmission schemes for particular application scenarios are presented.
Zukünftige Netze sollen in der Lage sein, eine Vielzahl verschiedener Dienste zu unterstützen. Dabei wird angenommen, dass sie oft keine statische Netzwerkstruktur haben und sich daher selbsttätig konfigurieren und automatisch an wechselnde Anforderungen sowie Netzwerksituationen und -änderungen anpassen sollen. Es ist wünschenswert, dass die benötigte Dienstqualität (QoS), im Besonderen für zeitkritische Anwendungen wie VoIP, automatisch gewährleistet werden kann. Das Netz soll zukünftigen Anforderungen gerecht werden, auch wenn diese zum Zeitpunkt der Erstellung noch nicht relevant oder bekannt sind. In diesem Dokument wird ein möglicher Ansatz des noch jungen Forschungsprojekts Self-NET für die Erfüllung der genannten Anforderungen skizziert und zur Diskussion gestellt.