Barbara Staehle

On max-min fair flow optimization in wireless mesh networks

The paper is devoted to modeling wireless mesh networks (WMN) through mixed-integer programming (MIP) formulations that allow to precisely characterize the link data rate capacity and transmission scheduling using the notion of time slots. Such MIP models are formulated for several cases of the modulation and coding schemes (MCS) assignment. We present a general way of solving the max-min fairness (MMF) traffic objective for WMN using the formulated capacity models. Thus the paper combines WMN radio link modeling with a non-standard way of dealing with uncertain traffic, a combination that has not, to our knowledge, been treated so far by exact optimization models. We discuss several ways, including a method based on the so called compatible or independent sets, of solving the arising MIP problems. We also present an extensive numerical study that illustrates the running time efficiency of different solution approaches, and the influence of the MCS selection options and the number of time slots on traffic performance of a WMN. Exact joint optimization modeling of the WMN capacity and the MMF traffic objectives forms the main contribution of the paper.

Using buffered playtime for QoE-oriented resource management of YouTube video streaming

YouTube is the most important online platform for streaming video clips. The popularity and the continuously increasing number of users pose new challenges for Internet service providers. In particular, in access networks where the transmission resources are limited and the providers are interested in reducing their operational expenditure, it is worth to efficiently optimise the network for popular services such as YouTube. In this paper, we propose different resource management mechanisms to improve the quality of experience (QoE) of YouTube users. In particular, we investigate the benefit of cross-layer resource management actions at the client and in the access network for YouTube video streaming. The proposed algorithms are evaluated in a wireless mesh testbed. The results show how to improve the YouTube QoE for the users with the help of client-based or network-based control actions. Copyright

Max-Min Fair Throughput in Multi-Gateway Multi-Rate Mesh Networks

The problem how to determine the capacity of and achieve fairness in mesh networks is one of the key topics in practical and theoretical research on mesh networks. Max-min fairness is one way to define fairness and several algorithms how to compute max-min fair rate allocations are already published. In this paper we make two major contributions to this area of research: First, we formulate an algorithm achieving max-min fairness among end-to-end flows based on the effective load of a collision domain. This allows us to determine max-min fair rate allocations in a multi-gateway, multi-channel mesh network with equal rates for all links. Second, we extend this algorithm for heterogeneous link rates.

Performance comparison of windows-based thin-client architectures

The basic idea behind thin-client architectures is to run applications on a central server instead of installing them separately on each client. The Windows remote desktop protocol (RDP) and the Citrix presentation server are two well known approaches to separate the location of where the user input is processed from the computer he is actually working on. While both alternatives solve the same problem, they rely on significantly different mechanisms to handle the exchange of user input and screen updates between client and server. In this paper we therefore compare the performance of both protocols under different aspects. In particular, we study the load caused on network layer as well as the satisfaction of the end user with the service quality achieved by the different terminal services. As this performance heavily depends on the current network conditions, we emulate realistic scenarios in a controlled testbed environment and measure the time required for typical office tasks on application layer. As a result, we quantify the Quality-of-Experience (QoE) perceived by the end-user, compare the overhead required by the different available protocols, and unveil their advantages and disadvantages. Our results can be used to decide which protocol to use in which scenario.

A genetic approach for wireless mesh network planning and optimization

Wireless Mesh Networks (WMNs) are gaining an increasingly important role in next generation last mile access. They offer more flexibility compared to traditional networks but on the expense of a complex structure. Thus, planning and optimization of WMNs is a challenge. In this paper we focus on routing and channel assignment in WMNs for throughput maximization using genetic algorithms. Genetic algorithms provide a good solution for large-scale WMNs in relatively small computation time. The results prove the effectiveness of the genetic operators and show the advantages of a genetic optimization. However, these operators have to be configured carefully to avoid local optima. We will show the influence of the selection principles as well as evaluation functions on the optimization.

Intra-Mesh Congestion Control for IEEE 802.11s Wireless Mesh Networks

Wireless mesh networks (WMNs) are a convenient type of Internet access networks, because they are self-configuring and self-healing wireless multi-hop networks. This is in particular true for IEEE 802.11 based WMNs as they cover large areas, are easy and cheap to setup, and provide sufficient capacity. Despite these advantages, WMNs have not yet entered the mass market. One of the reasons for this is, that many existing WLAN mesh networks use their own specific combination of higher layer protocols and IEEE 802.11 MAC extensions what makes it hard to characterize their performance and to provide interoperability. The recently published IEEE 802.11s-2011 standard addresses this issue by introducing standardized MAC layer mechanisms for WLAN mesh networking. One of these mechanisms is the IEEE 802.11s intra-mesh congestion control (IMCC) framework which addresses one of the key challenges in contention-based WMNs, namely congestion on the wireless medium. In this paper we quantify the benefits of this framework by introducing and evaluating three IEEE 802.11s-compliant IMCC algorithms. An extensive simulation study reveals that in dependence on the different levels of complexity of the algorithms-node-specific (TCC), link-specific (LSCC), or path-specific (PSCC)-the network performance in terms of throughput and fairness can be significantly improved.

Measuring one-way delay in wireless mesh networks: an experimental investigation

Wireless Mesh networks are multi-hop networks mostly based on IEEE 802.11 technology and are considered as a viable alternative for providing broadband wireless Internet access. As a consequence, they require support for Quality of Service or advanced mechanisms for selecting Internet gateways. One important required information is the one-way delay between different nodes. In this paper, we have developed, implemented, and evaluated an one-way delay estimation technique for wireless mesh networks which is based on estimating intra node queuing and inter node forwarding delay. An IP-header option field is used to accumulate the per hop delay estimate to provide an end-to-end estimate. We also outline problems with the implementation and compare results with real one-way delays obtained from a 14 node mesh testbed. We show how estimation accuracy depends on network load and provide insights into further improvements.

AquareYoum: Application- and Quality of Experience-Aware Resource Management for YouTube in Wireless Mesh Networks

Das Internet ermoglicht den Zugang zu einer Vielzahl von Diensten wie z.B. YouTube, Skype, Cloud Storage oder IPTV. Die vom Benutzer erfahrene Quality of Experience (QoE) oder Dienstgute ist jedoch oftmals nicht optimal, da die Netze keine Kenntnis uber die Dienste haben deren Daten sie transportieren. Daher werden IPTV Pakete, die in Echtzeit ausgeliefert werden mussen, genauso behandelt wie zu einem Dokument-Upload gehorende weniger zeitkritische Pakete, auch wenn eine Priorisierung von IPTV technisch moglich ware. Werden drahtlose Mesh Netze (WMNs) als Internetzugangsnetze genutzt, ist dieses Problem besonders akut, da Ressourcen knapper sind als in drahtgebundenen Zugangsnetzen. Im Rahmen des BMBF Projektes G-Lab1 entstand daher das Konzept Aquarema (Application and QoE-aware resource management), das ein auf Informationen der Anwendungsschicht reagierendes dynamisches Ressourcenmanagement (RM) fur WMNs vorschlagt [1]. Die Software-Suite AquareYoum ist eine konkrete Realisierung dieses Konzepts. AquareYoum vermeidet eine Unterbrechung eines YouTube-Videos, indem es eine solche vorhersagt und in diesem Fall die Verteilung der WMN-Ressourcen gezielt anpasst. Das Video wird flussig abgespielt und die QoE von YouTube Nutzern in diesem WMN verbessert.

Optimizing the Association Procedure for Low-Power 802.15.4 Nonbeacon Sensor Networks

Building wireless sensor networks based on the IEEE 802.15.4 standard is an interesting option, as the standard enables low-power, low data rate wireless communication. Many authors analyzed and optimized the operational phase of such networks. In contrast, the initial phase, containing the 802.15.4 association procedure, has mostly been neglected. In this paper, we therefore propose four optimization possibilities for the association procedure of a nonbeacon-enabled sensor network. Our results show that significant performance improvements in terms of association probability, speed, and energy consumptions can be achieved.

Genetic algorithms for wireless mesh network planning

The complex multi-hop structure of WMNs requires a careful network planning. In this paper, we investigate the usability of Genetic Algorithms (GAs) for such a planning approach. The simplicity of GAs allow us to examine a large number of network configurations in order to optimize the network throughput and to fairly distribute the resources. This is achieved with a max-min fair share throughput distribution and by evaluating node positions, routing configurations, and channel assignments. We adapt standard genetic operators and evaluate the influence of the operators on the performance. The results show that GAs are well-suited for planning WMNs.