Book or Conference Proceedings
Chapter (part of a book)
Article in journal, newspaper, or magazine
Burger, V., Zinner, T., Dinh-Xuan, L., Wamser, F., Tran-Gia, P.: A Generic Approach to Video Buffer Modeling using Discrete-Time Analysis.ACM Transactions on Multimedia Computing, Communications, and Applications (TOMM). (2018).
Zinner, T., Geissler, S., Lange, S., Gebert, S., Seufert, M., Tran-Gia, P.: A Discrete-Time Model for Optimizing the Processing Time of Virtualized Network Functions.Computer Networks.125,4-14 (2017).
The softwarization of networks promises cost savings and better scalability of network functions by moving functionality from specialized devices into commercial off-the-shelf hardware. Generalized computing hardware offers many degrees of adjustment and tuning, which can affect performance and resource utilization. One of these adjustments are interrupt moderation techniques implemented by modern network interface cards and operating systems. Using these, an administrator can optimize either for low latencies or low CPU overhead for processing of network traffic. In this work, an analytical model that allows the computation of relevant performance metrics like packet processing time and packet loss for generic virtualized network functions running on commodity hardware is presented. Based on this model, impact factors like average packet interarrival time, interarrival time distribution, and duration of the interrupt aggregation interval are studied. Furthermore, we significantly improve the computational tractability of this discrete-time model by proving and leveraging a property regarding its limit behavior. We also demonstrate that using this property does not affect the accuracy of the model in the context of realistic parameter combinations. Finally, the improved runtime for numerical evaluations allows administrators to dynamically adapt their interrupt mitigation settings to changing network conditions by recalculating optimal parameters.
Cofano, G., De Cicco, L., Zinner, T., Nguyen-Ngoc, A., Tran-Gia, P., Mascolo, S.: Design and Performance Evaluation of Network-assisted Control Strategies for HTTP Adaptive Streaming.ACM Transactions on Multimedia Computing, Communications, and Applications. (2017).
Lorenz, C., Hock, D., Scherer, J., Durner, R., Kellerer, W., Gebert, S., Gray, N., Zinner, T., Tran-Gia, P.: An SDN/NFV-enabled Enterprise Network Architecture Offering Fine-Grained Security Policy Enforcement.IEEE Communications Magazine.55,217 - 223 (2017).
In recent years, the number of attacks and threat vectors against enterprise networks have been constantly increasing in numbers and variety. In addition, new challenges arise not only to the level of provided security, but also to the scalability and manageability of the deployed countermeasures such as firewalls and intrusion detection systems. Despite these attacks, the main security systems, e.g., network firewalls, have remained rather unchanged. Due to the tight integration into the physical network’s infrastructure, a dynamic resource allocation to adapt the security measures to the current network conditions is a difficult undertaking. Therefore, in this work, we analyze and compare different architectural design patterns for the integration of SDN/NFV-based security solutions into enterprise networks.
Metter, C., Seufert, M., Wamser, F., Zinner, T., Tran-Gia, P.: Analytical Model for SDN Signaling Traffic and Flow Table Occupancy and its Application for Various Types of Traffic.IEEE Transactions on Network and Service Management.14,603-615 (2017).
Software Defined Networking (SDN) has emerged as a promising networking paradigm overcoming various drawbacks of current communication networks. The control and data plane of switching devices is decoupled and control functions are centralized at the network controller. In SDN, each new flow introduces additional signaling traffic between the switch and the controller. Based on this traffic, rules are created in the flow table of the switch, which specify the forwarding behavior. To avoid table overflows, unused entries are removed after a predefined time-out period. Given a specific traffic mix, the choice of this time-out period affects the trade-off between signaling rate and table occupancy. As a result, network operators have to adjust this parameter to enable a smooth and efficient network operation. Due to the complexity of this problem caused by the various traffic flows in a network, a suitable abstraction is necessary in order to derive valid parameter values in time. The contribution of this work is threefold. Firstly, we formulate a simple analytical model that allows optimizing the network performance with respect to the table occupancy and the signaling rate. Secondly, we validate the model by means of simulation. Thirdly, we illustrate the impact of the time-out period on the signaling traffic and the flow table occupancy for different data-plane traffic mixes and characteristics. This includes scenarios with single application instances, as well as multiple application instances of different application types in an SDN-enabled network.
Hoffmann, M., Jarschel, M., Pries, R., Schneider, P., Jukan, A., Bziuk, W., Gebert, S., Zinner, T., Tran-Gia, P.: SDN and NFV as Enabler for the Distributed Network Cloud.Mobile Networks and Applications. (2017).
Burger, V., Seufert, M., Hoßfeld, T., Tran-Gia, P.: Performance Evaluation of Backhaul Bandwidth Aggregation Using a Partial Sharing Scheme.Physical Communication.19,135-144 (2016).
To cope with the increasing demand of mobile devices and the limited capacity of cellular networks mobile connections are offloaded to WiFi. The access capacity is further increased, by aggregating bandwidth of WiFi access links. To analyse the performance of aggregated access links we model the most simple case of two cooperating systems interchanging capacities using an offloading scheme. The resulting analytic model is computed by means of a two-dimensional birth and death process. It can be used to seamlessly evaluate the performance of systems between partitioning and complete sharing. This allows to optimize the setting of thresholds dependent on the load of the cooperating system. Furthermore the benefit of aggregating bandwidth in different scenarios with homogeneous and heterogeneous workloads is quantified and the performance of more than two cooperating systems is evaluated by simulation.
Seufert, M., Burger, V., Lorey, K., Seith, A., Loh, F., Tran-Gia, P.: Assessment of Subjective Influence and Trust with an Online Social Network Game.Computers in Human Behavior.64,233-246 (2016).
The deduction of influence and trust between two individuals only from objective data in online social networks (OSNs) is a rather vague approach. Subjective assessments via surveys produce better results, but are harder to conduct considering the vast amount of friendships of OSN users. This work presents a framework for personalized surveys on relationships in OSNs, which follows a gamification approach. A Facebook game was developed, which was used to subjectively assess social influence and interpersonal trust based on models from psychology. The results show that it is possible to obtain subjective opinions and (limited) objective data about relationships with an OSN game. Also an implicit assessment of influence and trust with subcategory questions is feasible in this case.
Wamser, F., Casas, P., Seufert, M., Moldovan, C., Tran-Gia, P., Hoßfeld, T.: Modeling the YouTube Stack: from Packets to Quality of Experience.Computer Networks.109,211-224 (2016).
YouTube is one of the most popular and volume-dominant services in today’s Internet, and has changed the Web for ever. Consequently, network operators are forced to consider it in the design, deployment, and optimization of their networks. Taming YouTube requires a good understanding of the complete YouTube stack, from the network streaming service to the application itself. Understanding the interplays between individual YouTube functionalities and their implications for traffic and user Quality of Experience (QoE) becomes paramount nowadays. In this paper we characterize and model the YouTube stack at different layers, going from the generated network traffic to the QoE perceived by the users watching YouTube videos. Firstly, we present a network traffic model for the YouTube flow control mechanism, which permits to understand how YouTube provisions video traffic flows to users. Secondly, we investigate how traffic is consumed at the client side, deriving a simple model for the YouTube application. Thirdly, we analyze the implications for the end user, and present a model for the quality as perceived by them. This model is finally integrated into a system for real time QoE-based YouTube monitoring, highly useful to operators to assess the performance of their networks for provisioning YouTube videos. The central parameter for all the presented models is the buffer level at the YouTube application layer. This paper provides an extensive compendium of objective tools and models for network operators to better understand the YouTube traffic in their networks, to predict the playback behavior of the video player, and to assess how well they do it in the practice with the satisfaction of their customers watching YouTube.
Wamser, F., Blenk, A., Seufert, M., Zinner, T., Kellerer, W., Tran-Gia, P.: Modeling and Performance Analysis of Application-Aware Resource Management.International Journal of Network Management.25,223-241 (2015).
Application-aware resource management is the approach to tailor access networks to have characteristics beneficial for the running applications and services. This is achieved through the monitoring and integration of key performance indicators from the application layer within the network resource management. The aim is to increase user-perceived quality and network resource efficiency by traffic engineering with the help of these indicators. Using analytic and simulative approaches, this paper provides analysis methods for network operators to quantify the performance gains of alternative resource allocation algorithms that implement the application-aware concept. Network operators can use the proposed methods to evaluate possible performance gain trade-offs between investing in a pure capacity increase (over-provisioning) and the realization of an application-aware resource allocation. For this purpose, we model and analyze the application quality trade-offs of four algorithms for application-aware resource management at a single link in varying traffic situations. The algorithms are chosen with respect to different complexity and implementation level in order to cover the design space in a systematic way. The study of the algorithms focuses on the application-layer performance for the most used applications today, namely web browsing and video streaming with constant bit-rate as well as HTTP progressive streaming with variable bit-rate. Application quality trade-offs are analyzed in particular for a high resource utilization at a bottleneck link. The results confirm that application-aware resource management outperforms best-effort resource management in terms of QoE. Moreover, our study provides guidelines for the selection and configuration of the evaluated algorithms.
Hoßfeld, T., Seufert, M., Sieber, C., Zinner, T., Tran-Gia, P.: Identifying QoE Optimal Adaptation of HTTP Adaptive Streaming Based on Subjective Studies.Computer Networks.81,320-332 (2015).
HTTP Adaptive Streaming (HAS) technologies, e.g., Apple HLS or MPEG-DASH, automatically adapt the delivered video quality to the available network. This reduces stalling of the video but additionally introduces quality switches, which also influence the user-perceived Quality of Experience (QoE). In this work, we conduct a subjective study to identify the impact of adaptation parameters on QoE. The results indicate that the video quality has to be maximized first, and that the number of quality switches is less important. Based on these results, a method to compute the optimal QoE-optimal adaptation strategy for HAS on a per user basis with mixed-integer linear programming is presented. This QoE-optimal adaptation enables the benchmarking of existing adaptation algorithms for any given network condition. Moreover, the investigated concept is extended to a multi-user IPTV scenario. The question is answered whether video quality, and thereby, the QoE can be shared in a fair manner among the involved users.
Blenk, A., Basta, A., Kellerer, W., Zinner, T., Wamser, F., Tran-Gia, P.: Network Functions Virtualization (NFV) und Software Defined Networking (SDN): Forschungsfragen und Anwendungsfälle.ITG Mitgliederbeiträge / VDE dialog (invited article).10-13 (2015).
Lange, S., Gebert, S., Zinner, T., Tran-Gia, P., Hock, D., Jarschel, M., Hoffmann, M.: Heuristic Approaches to the Controller Placement Problem in Large Scale SDN Networks.IEEE Transactions on Network and Service Management - Special Issue on Efficient Management of SDN and NFV-based Systems.12,4 - 17 (2015).
Software Defined Networking (SDN) marks a paradigm shift towards an externalized and logically centralized network control plane. A particularly important task in SDN architectures is that of controller placement, i.e., the positioning of a limited number of resources within a network in order to meet various requirements. These requirements range from latency constraints to failure tolerance and load balancing. In most scenarios, at least some of these objectives are competing, thus no single best placement is available and decision makers need to find a balanced trade-off. This work presents POCO, a framework for Pareto-based Optimal COntroller placement that provides operators with Pareto optimal placements with respect to different performance metrics. In its default configuration, POCO performs an exhaustive evaluation of all possible placements. While this is practically feasible for small and medium sized networks, realistic time and resource constraints call for an alternative in the context of large scale networks or dynamic networks whose properties change over time. For these scenarios, the POCO toolset is extended by a heuristic approach that is less accurate, but yields faster computation times. An evaluation of this heuristic is performed on a collection of real world network topologies from the Internet Topology Zoo. Utilizing a measure for quantifying the error introduced by the heuristic approach allows an analysis of the resulting trade-off between time and accuracy. Additionally, the proposed methods can be extended to solve similar virtual functions placement problems which appear in the context of Network Functions Virtualization (NFV).
Seufert, M., Egger, S., Slanina, M., Zinner, T., Hoßfeld, T., Tran-Gia, P.: A Survey on Quality of Experience of HTTP Adaptive Streaming.IEEE Communications Surveys & Tutorials.17,469-492 (2015).
Changing network conditions pose severe problems to video streaming in the Internet. HTTP adaptive streaming (HAS) is a technology employed by numerous video services which relieves these issues by adapting the video to the current network conditions. It enables service providers to improve resource utilization and Quality of Experience (QoE) by incorporating information from different layers in order to deliver and adapt a video in its best possible quality. Thereby, it allows to take into account end user device capabilities, available video quality levels, current network conditions, and current server load. For end users, the major benefits of HAS compared to classical HTTP video streaming are reduced interruptions of the video playback and higher bandwidth utilization, which both generally result in a higher QoE. Adaptation is possible by changing the frame rate, resolution, or quantization of the video, which can be done with various adaptation strategies and related client- and server-side actions. The technical development of HAS, existing open standardized solutions, but also proprietary solutions are reviewed in this article as fundament to derive the QoE influence factors which emerge as a result of adaptation. The main contribution is a comprehensive survey of QoE related works from human computer interaction and networking domains which are structured according to the QoE impact of video adaptation. To be more precise, subjective studies which cover QoE aspects of adaptation dimensions and strategies are revisited. As a result, QoE influence factors of HAS and corresponding QoE models are identified, but also open issues and conflicting results are discussed. Furthermore, technical influence factors, which are often ignored in the context of HAS, affect perceptual QoE influence factors and are consequently analyzed. This survey gives the reader an overview of the current state of the art and recent developments. At the same time it targets networking researchers who develop new solutions for HTTP video streaming or assess video streaming from a user centric point of view. Therefore, the article is a major step towards truly improving HAS.
Pham Ngoc, N., Nguyen Huu, T., Vu Quang, T., Tran Hoang, V., Truong Thu, H., Tran-Gia, P., Schwartz, C.: A new power profiling method and power scaling mechanism for energy-aware NetFPGA gigabit router.Computer Networks. (2014).
Today the ICT industry accounts for 2–4% of the worldwide carbon emissions that are estimated to double in a business-as-usual scenario by 2020. A remarkable part of the large energy volume consumed in the Internet today is due to the over-provisioning of network resources such as routers, switches and links to meet the stringent requirements on reliability. Therefore, performance and energy issues are important factors in designing gigabit routers for future networks. However, the design and prototyping of energy-efficient routers is challenging because of multiple reasons, such as the lack of power measurements from live networks and a good understanding of how the energy consumption varies under different traffic loads and switch/router configuration settings. Moreover, the exact energy saving level gained by adopting different energy-efficient techniques in different hardware prototypes is often poorly known. In this article, we first propose a measurement framework that is able to quantify and profile the detailed energy consumption of sub-components in the NetFPGA OpenFlow switch. We then propose a new power-scaling algorithm that can adapt the operational clock frequencies as well as the corresponding energy consumption of the FPGA core and the Ethernet ports to the actual traffic load. We propose a new energy profiling method, which allows studying the detailed power performance of network devices. Results show that our energy efficient solution obtains higher level of energy efficiency compared to some existing approaches as the upper and lower bounds of power consumption of the NetFPGA Openflow switch are proved to be 30% lower than ones of the commercial HP Enterprise switch. Moreover, the new switch architecture can save up to 97% of dynamic power consumption of the FPGA chip at lowest frequency mode.
Hoßfeld, T., Keimel, C., Hirth, M., Gardlo, B., Habigt, J., Diepold, K., Tran-Gia, P.: Best Practices for QoE Crowdtesting: QoE Assessment with Crowdsourcing.Transactions on Multimedia.16, (2014).
Quality of Experience (QoE) in multimedia applications is closely linked to the end users’ perception and therefore its assessment requires subjective user studies in order to evaluate the degree of delight or annoyance as experienced by the users. QoE crowdtesting refers to QoE assessment using crowdsourcing, where anonymous test subjects conduct subjective tests remotely in their preferred environment. The advantages of QoE crowdtesting lie not only in the reduced time and costs for the tests, but also in a large and diverse panel of international, geographically distributed users in realistic user settings. However, conceptual and technical challenges emerge due to the remote test settings. Key issues arising from QoE crowdtesting include the reliability of user ratings, the influence of incentives, payment schemes and the unknown environmental context of the tests on the results. In order to counter these issues, strategies and methods need to be developed, included in the test design, and also implemented in the actual test campaign, while statistical methods are required to identify reliable user ratings and to ensure high data quality. This contribution therefore provides a collection of best practices addressing these issues based on our experience gained in a large set of conducted QoE crowdtesting studies. The focus of this article is in particular on the issue of reliability and we use video quality assessment as an example for the proposed best practices, showing that our recommended two-stage QoE crowdtesting design leads to more reliable results.
Schwerdel, D., Reuther, B., Zinner, T., Müller, P., Tran-Gia, P.: Future Internet Research and Experimentation: The G-Lab Approach.Computer Networks. (2014).
The German Lab (G-Lab) project aims to investigate architectural concepts and technologies for a new inter-networking architecture as an integrated approach between theoretic and experimental studies. Thus G-Lab consists of two major fields of activities: research studies of future network components and the design and setup of experimental facilities. Both are controlled by the same community to ensure that the experimental facility meets the demands of the researchers. Researchers gain access to virtualized resources or may gain exclusive access to resources if necessary. We present the current setup of the experimental facility, describing the available hardware, management of the platform, the utilization of the PlanetLab software and the user management. Moreover, a new approach to setup and deploy virtual network topologies will be described.
Jarschel, M., Zinner, T., Hoßfeld, T., Tran-Gia, P., Kellerer, W.: Interfaces, Attributes, and Use Cases: A Compass for SDN.IEEE Communications Magazine.52,210-217 (2014).
The term Software Defined Networking (SDN) is prevalent in today’s discussion about future communication networks. As with any new term or paradigm, however, no consistent definition regarding this technology has formed. The fragmented view on SDN results in legacy products being passed off by equipment vendors as SDN, academics mixing up the attributes of SDN with those of network virtualization, and users not fully understanding the benefits. Therefore, establishing SDN as a widely adopted technology beyond laboratories and insular deployments requires a compass to navigate the multitude of ideas and concepts that make up SDN today. The contribution of this article represents an important step toward such an instrument. It gives a thorough definition of SDN and its interfaces as well as a list of its key attributes. Furthermore, a mapping of interfaces and attributes to SDN use cases is provided, highlighting the relevance of the interfaces and attributes for each scenario. This compass gives guidance to a potential adopter of SDN on whether SDN is in fact the right technology for a specific use case.
Hoßfeld, T., Seufert, M., Sieber, C., Zinner, T., Tran-Gia, P.: Close to Optimum? User-centric Evaluation of Adaptation Logics for HTTP Adaptive Streaming.PIK - Praxis der Informationsverarbeitung und Kommunikation.37,275-285 (2014).
HTTP Adaptive Streaming (HAS) is the de-facto standard for over-the-top (OTT) video streaming services. It allows to react to fluctuating network conditions on short time scales by adapting the video bit rate in order to avoid stalling of the video playback. With HAS the video content is split into small segments of a few seconds playtime each, which are available in different bit rates, i.e., quality level representations. Depending on the current conditions, the adaptation algorithm on the client side chooses the appropriate quality level and downloads the respective segment. This allows to avoid stalling, which is seen as the worst possible disturbance of HTTP video streaming, to the most possible extend. Nevertheless, the user perceived Quality of Experience (QoE) may be affected, namely by playing back lower qualities and by switching between different qualities. Therefore, adaptation algorithms are desired which maximize the user’sQoEfor the currently available network resources. Many downloading strategies have been proposed in literature, but a solid user-centric comparison of these mechanisms among each other and with the global optimum is missing. The major contributions of this work are as follows. A proper analysis of the influence of quality switches and played out representations on QoE is conducted by means of subjective user studies. The results suggest that, in order to optimize QoE, first, the quality level of the video stream has to be maximized and second, the number of quality switches should be minimized. Based on our findings, a QoEoptimization problem is formulated and the performance of our proposed algorithm is compared to other algorithms and to the QoE-optimal adaptation.
Hoßfeld, T., Burger, V., Hinrichsen, H., Hirth, M., Tran-Gia, P.: On the computation of entropy production in stationary social networks.Social Network Analysis and Mining.4, (2014).
Completing their initial phase of rapid growth, social networks are expected to reach a plateau from where on they are in a statistically stationary state. Such stationary conditions may have different dynamical properties. For example, if each message in a network is followed by a reply in opposite direction, the dynamics is locally balanced. Otherwise, if messages are ignored or forwarded to a different user, one may reach a stationary state with a directed flow of information. To distinguish between the two situations, we propose a quantity called entropy production that was introduced in statistical physics as a measure for non-vanishing probability currents in nonequilibrium stationary states. The proposed quantity closes a gap for characterizing online social networks. As major contribution, we show the relation and difference between entropy production and existing metrics. The comparison shows that computational intensive metrics like centrality can be approximated by entropy production for typical online social networks. To compute the entropy production from real-world measurements, the need for Bayesian inference and the limits of naïve estimates for those probability currents are shown. As further contribution, a general scheme is presented to measure the entropy production in small-world networks using Bayesian inference. The scheme is then applied for a specific example of the R mailing list.
Hock, D., Wamser, F., Seufert, M., Pries, R., Tran-Gia, P.: OC²E²AN: Optimized Control Center for Experience Enhancements in Access Networks.PIK - Praxis der Informationsverarbeitung und Kommunikation.36,40 (2013).
Tran-Gia, P., Hoßfeld, T., Hartmann, M., Hirth, M.: Crowdsourcing and its Impact on Future Internet Usage.it - Information Technology.55,139-145 (2013).
Crowdsourcing is an emerging service platform and business model in the Internet. In contrast to outsourcing where a job is performed by a designated contractor, with Crowdsourcing, jobs are outsourced to a large, anonymous crowd of workers, the so-called human cloud. The rise of Crowdsourcing and its seamless integration in current workflows may have a huge impact on the Internet and on society, and will be a guiding paradigm that can form the evolution of work in the years to come. In this article, we discuss applications and use cases of Crowdsourcing to demonstrate the impact on Internet usage. Novel measurement approaches are presented and the impact of Crowdsourcing on Internet traffic is evaluated by measuring the activity of a particular Crowdsourcing platform. New technical solutions are necessary for the operation of efficient, distributed Crowdsourcing platforms. Special attention is drawn to the integration of machine clouds and human crowds, and appropriate inter-cloud solutions. Finally, we discuss current research challenges from a scientific and from the platform provider’s point of view.
Zinner, T., Hoßfeld, T., Tran-Gia, P., Kellerer, W.: Software defined Networks - Das Internet flexibler gestalten und dynamischer steuern.ITG Mitgliederbeilage / VDE dialog (invited article).6-9 (2013).
Vor allem aufgrund seiner starren Architektur und mangelnden Ressourcennutzung ist die Flexibilität der aktuellen Internettechnologie eingeschränkt. Dies könnte sich durch Anwendung von Software Defined Networks (SDN) ändern. Hierbei wird die Steuerung der Netze und Datenflüsse von den bisherigen Netzkomponenten auf eine zentrale logische Einheit übertragen.
Hoßfeld, T., Hirth, M., Tran-Gia, P.: Crowdsourcing - Modell einer neuen Arbeitswelt im Internet.Informatik Spektrum, Wirtschaftsinformatik & Management.5, (2013).
Das Internet hat bereits viele höchst erfolgreiche Geschäftsmodelle hervorgebracht. Jedoch basierten bisher die meisten neuen Anwendungen oder Dienstleistungen auf technischen Neuerungen, beispielsweise schnelleren Rechner, kürzeren Verbindungsdauern oder auf neuartigen algorithmischen Ansätzen, etwa der Page-Rank-Algorithmus von Google. Erst mit den Sozialen Medien wie Youtube oder Facebook wurden die Nutzer ein integraler Bestandteil der Wertschöpfungskette, ohne die das „Produkt“ nicht funktioniert. Einen ähnlich starken Einfluss auf den Erfolg eines Unternehmens haben Nutzer in Geschäftsmodellen, die auf dem Crowdsourcing-Paradigma beruhen, welches im Folgenden genauer beleuchtet werden soll.
Klein, D., Tran-Gia, P., Hartmann, M.: Aktuelles Schlagwort: Big Data.Informatik-Spektrum.36,319-323 (2013).
Big Data ist neben Cloud Computing und Crowdsourcing eine der wichtigsten neuen Technologie-Treiber und wird daher im Aktuellen Schlagwort näher beleuchtet. Zu Beginn gehen wir auf die Definition von Big Data ein und erläutern die Unterschiede zu traditionellen Verfahren. Im Anschluss daran stellen wir zugrundeliegende Technologien vor und geben einen kurzen Überblick über wissenschaftliche Herausforderungen in diesem Bereich.
Wamser, F., Hock, D., Seufert, M., Staehle, B., Pries, R., Tran-Gia, P.: Using Buffered Playtime for QoE-Oriented Resource Management of YouTube Video Streaming.Transactions on Emerging Telecommunications Technologies.24,288–302 (2013).
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 (ISPs). 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 optimize 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.
Schwartz, C., Hoßfeld, T., Lehrieder, F., Tran-Gia, P.: Angry Apps: The Impact of Network Timer Selection on Power Consumption, Signalling Load, and Web QoE.Journal of Computer Networks and Communications.1 - 22 (2013).
The popularity of smartphones and mobile applications has experienced a considerable growth during recent years and this growth is expected to continue in the future. Since smartphones have only very limited energy resources, battery efficiency is one of the deter- mining factors for a good user experience. Therefore, some smartphones tear down connec- tions to the mobile network soon after a completed data transmission to reduce the power consumption of their transmission unit. However, frequent connection re-establishments caused by apps which send or receive small amounts of data often lead to a heavy signalling load within the mobile network. One of the major contributions of this article is the investigation of the resulting trade-off between energy consumption at the smartphone and the generated signalling traffic in the mobile network. We explain that this trade-off can be controlled by the connection release timeout and study the impact of this parameter for a number of popular apps that cover a wide range of traffic characteristics in terms of bandwidth requirements and resulting signalling traffic. Finally, we study the impact of the timer settings on QoE for web traffic. This is an important aspect since connection establishments do not only lead to signalling traffic, but they also increase the load time of web pages.
Hoßfeld, T., Hirth, M., Tran-Gia, P.: Aktuelles Schlagwort: Crowdsourcing.Informatik Spektrum.35, (2012).
Seit der Öffnung des Internets für die Allgemeinheit Anfang der 90er Jahre hat eine rasante Entwicklung stattgefunden. Neue Paradigmen wie Peer-to-Peer (P2P), Web 2.0 oder Cloud Computing führen zu neuartigen Diensten und Anwendungen, welche bei den Anwendern längst etabliert sind und einen Großteil des Datenverkehrs im Internet ausmachen. Beispiele hierfür sind unter anderem P2P-Anwendungen wie BitTorrent zum Austausch riesiger Datenmengen, Skype für Sprach- und Videokonferenzen, Soziale Medien wie Facebook oder Twitter, Cloud Anwendungen wie DropBox als synchronisiertes Netzwerk-Dateisystem für verteilte Rechner oder Cloud Gaming. Aktuell taucht ein neues Schlagwort im Internet auf: „Crowdsourcing“. Einige Aufgaben und Probleme, die für Menschen relativ einfach zu lösen sind, können derzeit selbst von modernen Machine Clouds noch nicht algorithmisch bewältigt werden. Hierzu zählen etwa Text- und Bilderkennung, das Verifizieren, Analysieren und Kategorisieren von Videoinhalten, das Schaffen von Wissen, das Verbessern und Kreieren von Produkten oder wissenschaftliche Forschung. Diese stellen Anwendungsgebiete von Crowdsourcing dar. Statt (oder zusätzlich zu) Machine Clouds wird die Masse der Internetnutzer in die Wertschöpfungskette eingebunden. Man spricht hier auch von Human Clouds. Neben Sozialen Medien ist Crowdsourcing eine der wichtigsten aktuell aufstrebenden Technologien und Geschäftsmodelle im Internet, die die Zukunft des Arbeitens und der Arbeitsorganisation von Grund auf verändern wird. Die wirtschaftliche und gesellschaftliche Bedeutung von Crowdsourcing-Plattformen wächst ständig und fördert die Entstehung neuer Formen der Arbeitsorganisation. Jobs in Crowdsourcing-Plattformen besitzen eine viel kleinere Granularität im Vergleich zu denen im traditionellen Outsourcing bzw. Outtasking Bereich. Das Aktuelle Schlagwort beleuchtet den Begriff „Crowdsourcing“ näher und wird zunächst wichtige Begriffe einführen, bevor die Anwendungsgebiete von Crowdsourcing sowie dessen Bedeutung in der Praxis und zukünftige Weiterentwicklung betrachtet werden.
Hirth, M., Hoßfeld, T., Tran-Gia, P.: Analyzing Costs and Accuracy of Validation Mechanisms for Crowdsourcing Platforms.Mathematical and Computer Modelling. (2012).
Crowdsourcing is becoming more and more important for commercial purposes. With the growth of crowdsourcing platforms like Amazon Mechanical Turk or Microworkers, a huge work force and a large knowledge base can be easily accessed and utilized. But due to the anonymity of the workers, they are encouraged to cheat the employers in order to maximize their income. Thus, this paper we analyze two widely used crowd-based approaches to validate the submitted work. Both approaches are evaluated with regard to their detection quality, their costs and their applicability to different types of typical crowdsourcing tasks
Hoßfeld, T., Tran-Gia, P.: EuroView 2010: Visions of Future Generation Networks.Computer Communications Review CCR.Volume 41, Number 2, (2011).
On August 2nd – 3rd, 2010, the EuroView 2010 workshop on 'Visions of Future Generation Networks' was held at the University of Würzburg. The event was sponsored by the European Network of Excellence Euro-NF, the German Information Technology Society ITG, and the International Teletraffic Congress ITC. EuroView 2010 brought together Internet and network technology researchers, network providers, as well as equipment and device manufacturers. In 2010, the focus was on 'Future Internet Design and Experimental Facilities' and on current efforts towards a Future Internet. Special sessions were organized reflecting the latest results of selected testbed expert groups as well as current and future national and international collaborative projects: (1) the German G-Lab project offering a national platform for Future Internet studies, (2) the Future Internet Activities in the European Framework FP7 organized by Max Lemke, and (3) the GENI project in US organized by Aaron Falk. A keynote talk was given by Lawrence Landweber on the challenges and paradigms emerging in the Future (Inter)Network.
Zinner, T., Tutschku, K., Nakao, A., Tran-Gia, P.: Performance Evaluation of Packet Re-ordering on Concurrent Multipath Transmissions for Transport Virtualization.JCNDS Special Issue on: Network Virtualization - Concepts and Performance Aspects.Vol. 6,322-340 (2011).
From the viewpoint of communication networks Network Virtualization (NV) extends beyond pure operational issues and addresses many impasses of the current Internet. The idea of Transport Virtualization (TV) progresses the capabilities of NV and enables the independence from a specific network transport resource. The independence is achieved by pooling multiple transport resources and selecting the best resources for exclusive or concurrent use. However, the application and selection of concurrent paths is rather complex and introduces inevitable packet re-ordering due to different stochastic delay characteristics on the used paths. Packets arriving at the destination out-of-order have to be stored in a re-sequencing buffer before reassembled packets are forwarded to the application. We provide a simulation framework based on discrete event simulation which allows an evaluation of the re-sequencing buffer occupancy. Further, we perform an analysis of the fundamental behaviors and factors for packet re-ordering in concurrent multipath transmissions.
Wamser, F., Pries, R., Staehle, D., Heck, K., Tran-Gia, P.: Traffic characterization of a residential wireless Internet access.Special Issue of the Telecommunication Systems (TS) Journal.48: 1-2, (2010).
Traffic characterization is an important means for Internet Service Providers (ISPs) to adapt and to optimize their networks to the requirements of the customers. Most network measurements are performed in the backbone of these ISPs, showing both, residential and business Internet traffic. However, the traffic characteristics of business and home users differ significantly. Therefore, we have performed measurements of home users at a broadband wireless access service provider in order to reflect only home user traffic characteristics. In this paper, we present the results of these measurements, showing daily traffic fluctuations, flow statistics as well as application distributions. The results show a difference to backbone traffic characteristics. Furthermore, we observed a shift from web and Peer-to-Peer (P2P) file sharing traffic to streaming applications.
Pries, R., Staehle, D., Staehle, B., Tran-Gia, P.: On Optimization of Wireless Mesh Networks using Genetic Algorithms.International Journal On Advances in Internet Technology.1&2, (2010).
Wamser, F., Mittelstädt, D., Staehle, D., Tran-Gia, P.: Impact of Electrical and Mechanical Antenna Downtilt on a WiMAX System with Fractional Frequency Reuse.FREQUENZ - Journal of RF-Engineering and Telecommunications.September/October, (2010).
In an interference-limited mobile WiMAX network, efficient cell planning and tuning is an essential task to ensure a functioning network. This includes the selection of the optimal settings for the antenna to, on the one hand provide a good coverage and on the other hand achieve cell isolation. Two different antenna tilting methods are examined in this article, namely the mechanical and the electrical vertical downtilt. The evaluation is done with an advanced WiMAX IEEE 802.16e simulator. In particular, the impact of the antenna configuration on WiMAX fractional frequency reuse (FFR) is studied. The results show a high dependency of FFR to the downtilt configuration, since the inter-cell interference level changes significantly with different settings.
Fiedler, M., Hoßfeld, T., Tran-Gia, P.: A Generic Quantitative Relationship between Quality of Experience and Quality of Service.IEEE Network Special Issue on Improving QoE for Network Services. (2010).
Quality of Experience (QoE) ties together user perception, experience and expectations to application and network performance, typically expressed by Quality of Service (QoS) parameters. Quantitative relationships between QoE and QoS are required in order to be able to build effective QoE control mechanisms onto measurable QoS parameters. On this background, this paper proposes a generic formula in which QoE and QoS parameters are connected through an exponential relationship, called IQX hypothesis. The formula relates changes of QoE with respect to QoS to the current level of QoE, is simple to match, and its limit behaviours are straighforward to interpret. It validates the IQX hypothesis for streaming services, where QoE in terms of Mean Opinion Scores (MOS) is expressed as functions of loss and reordering ratio, the latter of which is caused by jitter. For web surfing as the second application area, matchings provided by the IQX hypothesis are shown to outperform previously published logarithmic functions. We conclude that the IQX hypothesis is a strong candidate to be taken into account when deriving relationships between QoE and QoS parameters.
Tran-Gia, P., Hoßfeld, T., Menth, M., Pries, R.: Emerging Issues in Current Future Internet Design.e&i Elektrotechnik und Informationstechnik, Special Issue 'Future Internet', ISSN: 0932-383X (print), ISSN: 1613-7620 (online).07/08, (2009).
From its inception, the Internet was not intended as the worldwide universal communication platform. It developed over almost four decades to its current state. As a result of this unplanned evolution, we currently witness scalability problems, increased complexity, missing modularity as well as missing flexibility for emerging services. In this report we focus on two selected issues: i) the changing routing paradigm and ii) edge‐based intelligence. We will then present a variety of projects on future Internet and finally assess recently established experimental facilities and their role in the Future Internet design.
Menth, M., Hartmann, M., Tran-Gia, P., Klein, D.: Future Internet Routing: Motivation and Design Issues.it - Information Technology.50(6), (2008).
Pre-congestion notification (PCN) in IP networks uses packet metering and marking within a PCN domain to notify its egress nodes whether link-specific admissible or supportable rate thresholds have been exceeded by high priority traffic. Based on this information simple admission control and flow termination is implemented. The latter is a new flow control function and useful in case of overload through high priority traffic which can occur in spite of admission control, e.g., when traffic is rerouted in failure cases. Resilient admission control admits only so much traffic that admitted traffic can be rerouted without causing congestion on backup paths in case of a likely failures, e.g., single link failures. We propose algorithms to configure the link-specific PCN rate thresholds such that resources are utilized efficiently and fairly by competing traffic aggregates while meeting resilience constraints. This is done for the single and dual marking PCN architecture whereby the single marking case is more demanding since it requires that the supportable rate is a fixed multiple of the admissible rate on all links within a single PCN domain. Furthermore, we derive objective functions to optimize the underlying routing system for both cases. Our performance results for various network types show that the dual marking PCN architecture leads to significantly better resource efficiency than the single marking PCN architecture.
Tran-Gia, P., Andersen, F.-U., Tutschku, K.: Trends in Network and Service Operation for the Emerging Future Internet.International Journal of Electronics and Communication. (2008).
Tran-Gia, P., Fritsch, T., Gihr, O.: Linear algorithm solving the travelling salesman optimization problem.IBM Technical Disclosure Bulletin.37(06B):265, (2007).
Tran-Gia, P., Mandjes, M.: Modeling of customer retrial phenomenon in cellular mobile networks.IEEE JSAC special issue on Personal Communication - Services, architecture and performance issues.1406--1414 (2007).
Tran-Gia, P., Tutschku, K.: Spatial traffic estimation and characterization for mobile communication network design.IEEE JSAC.16, (2007).
Tran-Gia, P., Kniffki, K.-D., Braun, C., Klusch, A.: Fluctuations in Bipolar Affective Illnes.Fractal Reviews in the Natural and Applied Sciences. (2007).
Leibnitz, K., Tran-Gia, P., Tutschku, K.: Teletraffic Issues in Mobile Communication Network Planning.Telecommunication Systems.15, (2007).
Tran-Gia, P., Jans, H., Manfield, D.: Modelling and Performance of Inter-Processor Messaging in Distributed Systems.Performance Evaluation.7, (2007).
Tran-Gia, P., Ritter, M.: Mechanismen zur Steuerung und Verwaltung von ATM-Netzen (Mechanisms for ATM network control and managment).Informatik Spektrum.20,216--224 (2007).
Tran-Gia, P., Staehle, D., Leibnitz, K.: Source Traffic Modeling of Wireless Applications.International Journal of Electronics and Communications.55, (2007).
de Meer, H., Tran-Gia, P., Tutschku, K.: Dynamic Operation in Peer-to-Peer Overlay Networks.Praxis der Informationsverarbeitung und Kommunikation - Special Issues on Peer-to-Peer Systems. (2007).
Binzenhöfer, A., Schnabel, H., Tran-Gia, P.: Methods for Performance Improvement of Kademlia-based Overlay Networks.it - Information Technology (Methods and Applications of Informatics and Information Technology).46, (2007).
Mandel, W., Kniffki, K.-D., Tran-Gia, P.: Temporal fluctuations in biorhythms: expression of self-organized criticality?Fractals.1,380--387 (1997).
Gropp, O., Tran-Gia, P.: Structure and performance of neural nets in broadband system admission control.Neural networks in Telecommunications, B. Yuhas and N. Ansari, editors, Kluwer, Boston.chapter 7, pp. 127-1, (1994).
Tran-Gia, P., Hübner, F.: Discrete-time analysis of cell spacing in ATM systems.Telecommunications Systems.3,379--395 (1994).
Tran-Gia, P., Ritter, M.: Multi-rate models for dimensioning and performance evaluation of ATM networks.Interim report, Cooperation in the Field of Science and Technical Research COST 242. (1994).
Tran-Gia, P.: Discrete-time analysis of usage parameter control functions in ATM systems.Architecture and protocols for high-speed networks, O. Spaniol, A.Danthine, and W.Effelsberg, editor.chapter 7, pp. 111-1, (1994).
Tran-Gia, P., Fritsch, T., Mittler, M.: Artificial neural net applications in telecommunication systems.Neural Computing & Applications.1,124--146 (1993).
Gold, H., Tran-Gia, P., Grob, H.: A batch service system operating in a pull production line.Archiv für Elektronik und Übertragungstechnik.47,379--385 (1993).
Gold, H., Tran-Gia, P.: Performance analysis of a batch service queue arising out of manufacturing system modelling.Queueing Systems.14,413--426 (1993).
Stock, T., Tran-Gia, P., Dittmann, R.: Das DQDB-Zugriffsprotokoll in Hochgeschwindigkeitsnetzen und der IEEE-Standard 802.6.Informatik-Spektrum.16,143--158 (1993).
Tran-Gia, P., Hübner, F.: Performance of a finite-capacity asynchronous multiplexer with modulated input.Telecommunication systems: Modeling, Analysis, Design and Management.1,263--278 (1993).
Tran-Gia, P.: Analysis of polling systems with general input process and finite capacity.IEEE Transactions on Communications.Vol. 40, No. 2, pp., (1992).
Gihr, O., Gold, H., Tran-Gia, P.: Analytische Modellbildung von Fertigungssystemen - Eine Fallstudie.Informatik als Produktionsfaktor. (1992).
Dittmann, R., Tran-Gia, P.: A discrete-time analysis of the cyclic reservation multiple access protocol.Performance Evaluation.16,263--278 (1992).
Tran-Gia, P., Stock, T.: Approximate performance analysis of the DQDB access protocol.Computer Network and ISDN Systems.20,231--240 (1990).
Tran-Gia, P.: A Class of Renewal Interrupted Poisson Processes and Applications to Queueing Systems.Zeitschrift für Operations Research.vol. 32, (1988).
Tran-Gia, P., Raith, T.: Performance Analysis of Finite Capacity Polling Systems with Nonexhaustive Service.Perfomance Evaluation.vol. 9, (1988).
Tran-Gia, P., Van Hoorn, M.H.: Dependency of Service Time on Waiting Time in Switching Systems - A Queueing Analysis with Aspects of Overload Control.IEEE Transactions on Communications.34, (1986).
Tran-Gia, P., Jans, H.: Delay Analysis of Clock-Driven Message Transfer in Distributed Processing Systems.Archiv für Elektronik und Übertragungstechnik.39,285-292 (1985).
In modern computer and communication systems the system of control is distributed among a number of individual devices or processors operating in modes of function or load sharing. Communication between distributed control units via an interconnection network is often organized in the form of message interchanging according to message transfer mechanism. In this paper, a performance analysis is given for the commonly used clock-driven messaging protocol, for which a two-level queueing system is developed and investigated. The analysis is done using a two-dimensional imbedded Markov chain, for which the calculation is done in conjunction with a dimension reducing choice of regression points. Numerical results for dimensioning purposes are given for message delay characteristics under different traffic conditions, clock intervals, and buffer sizes. The results can be used to optimize the messaging delay for the class of clock-driven message transfer mechanisms. Finally, the distribution function of the queueing delay is derived for the first-in first-out message transfer discipline.
Tran-Gia, P., Manfield, D.: Analysis of a Storage System with Batch Input Arising out of Message Packetisation.IEEE Transactions on Communications.30, (1982).
Article in Conference Proceedings
Karagkioules, T., Tsilimantos, D., Valentin, S., Wamser, F., Zeidler, B., Seufert, M., Loh, F., Tran-Gia, P.: A Public Dataset for YouTube’s Mobile Streaming Client.TMA Conference (2018).
Lange, S., Reinhart, L., Zinner, T., Hock, D., Gray, N., Tran-Gia, P.: Integrating Network Management Information into the SDN Control Plane.IEEE/IFIP Network Operations and Management Symposium (NOMS) (2018).
With software defined networking (SDN), operators benefit from a higher flexibility, cost efficiency, as well as programmability of their networks. Since modern networks are comprised of a multitude of heterogeneous devices and also include non-SDN legacy devices, network management systems (NMSs) are often used in order to monitor and configure the network. Although both, the SDN controller and the NMS, have a centralized view of the network, they operate at different time scales and deal with information at different levels of granularity. In this work, we investigate the impact on the network performance when an NMS regularly provides information to an SDN controller. To this end, we design, implement, and compare three interaction mechanisms based on the ONOS controller. These represent different trade-offs regarding the complexity of the resulting system and its performance. In addition to the default ONOS controller, we develop two extended versions. One performs hash-based load balancing on equal cost paths while the other utilizes external NMS information via ONOS's intent and annotation framework to optimize control plane decisions. In addition to evaluations that show a significant performance improvement when using the optimized controllers, we present a parameter study that highlights the performance impact of network characteristics like the flow interarrival time, the flow duration, and the number of active flows.
Wamser, F., Lombardo, C., Vassilakis, C., Dinh-Xuan, L., Lago, P., Bruschi, R., Tran-Gia, P.: Orchestration and Monitoring in Fog Computing for Personal Edge Cloud Service Support.2018 IEEE International Symposium on Local and Metropolitan Area Networks (LANMAN) (2018).
Nguyen-Ngoc, A., Lange, S., Geissler, S., Zinner, T., Tran-Gia, P.: Estimating the Flow Rule Installation Time of SDN Switches when Facing Control Plane Delay.19th International GI/ITG Conference on “Measurement, Modelling and Evaluation of Computing Systems”. , Erlangen (2018).
The software defined networking (SDN) paradigm has numerous benefits for network operators, including cost aspects, flexibility, and programmability. In the centralized SDN architecture, the controller can order the installation of flow rules in the switches it manages via FlowMod messages. Since the processing time of these messages has a direct impact on the reaction time of the network, it is a key performance indicator for switches and quantifying it in a reliable manner is required for ensuring state consistency between the control and the data plane. Furthermore, real world deployments not only consist of different data plane hardware, but may feature varying control plane delays. Hence, in this work, we investigate the impact of such a delay on the FlowMod processing time of OpenFlow switches. Firstly, we identify a significant heterogeneity between data plane hardware in terms of processing times as well as the underlying TCP-level behavior. Secondly, we show that despite this heterogeneity, combining switch specific information with delay measurements at the controller can be used to reliably infer FlowMod processing times. We confirm our results with measurements in a dedicated testbed that is comprised of three different hardware switches, three different SDN controllers, and several high precision measurement devices.
Loh, F., Wamser, F., Hoßfeld, T., Tran-Gia, P.: Quality of Service Assessment of Live Video Streaming with a Remote-Controlled Drone.IEEE Conference on Network Softwarization. , Montreal, Canada (2018).
Today's networks require a deep understanding of applications to optimize networks, efficiently design networks, and meet traffic demands, application heterogeneity, and application requirements. Current application areas include live video streaming and real-time applications, such as those that are named in 5G use cases with automation, disaster recovery, gaming, and Industry 4.0. In this work, we examine an application scenario with live video streaming and parallel real-time requirements in the uplink for disaster recovery. We study the quality of service (QoS) features of a remote-controlled drone. The drone is controlled via a tablet or smartphone while the video from the camera is transmitted from the drone to the user. There are high demands in both the uplink and downlink direction. The contribution of the work is the measurement of the QoS and application parameters for this scenario and the definition of influencing parameters for the application-layer.
Nguyen-Ngoc, A., Raffeck, S., Lange, S., Geissler, S., Zinner, T., Tran-Gia, P.: Benchmarking the ONOS Controller with OFCProbe.7th International Conference on Communications and Electronics (ICCE). , Hue, Vietnam (2018).
The increased popularity of Software Defined Networking (SDN) drives the development and research of all involved components. In particular, state-of-the-art SDN controllers are a central part of the resulting network architecture and have a large impact on the performance of the entire network. Hence, it is necessary to quantify various performance indicators of the SDN controller in order to assess its feasibility in the context of different network characteristics such as topology and network size w.r.t. the number of nodes and links. To this end, we extend the open-source controller benchmarking tool OFCProbe with several novel modules that are capable of recording relevant performance metrics and demonstrate their use in the context of benchmarking the ONOS controller. Furthermore, we investigate the impact of different types of topology characteristics on the performance of the controller. In this work, we focus on several performance indicators for SDN controllers. First, the time that the ONOS controller needs to discover the network topology and update its internal representation of the topology. Second, we investigate the duration of the installation of flow rules that are used for reactive path provisioning. Finally, we measure the response time of the controller when dealing with asynchronous messages.
Dinh-Xuan, L., Seufert, M., Wamser, F., Vassilakis, C., Zafeiropoulos, A., Tran-Gia, P.: Performance Evaluation of Service Functions Chain Placement Algorithms in Edge Cloud.30th International Teletraffic Congress (ITC30). , Vienna, Austria (2018).
The emergence of Network Function Virtualization (NFV) paradigm has become a potential solution dealing with the rapid growth of the global Internet traffic in the last decades. There, network appliances are transformed into Virtual Network Functions (VNF) running on a standard server. This promises to significantly reduce overall cost and energy consumption. Additionally, hardware-based network function chain is replaced by a chain of the VNFs, called Service Function Chain (SFC). The expected benefit of SFC is the reduction in the complexity when deploying heterogeneous network services. However, the considerable drawback of SFC is the distribution of the VNFs over different hosts. An inefficient placement of VNFs can induce a high latency within the chain and wasted server resources. In this work, we propose four placement algorithms that aim to efficiently place the SFC in servers with regard to minimizing service response time and resource utilization. Herein, heuristic approaches are evaluated against optimal solutions for the placement problems, which are formulated by using Integer Linear Programming. We evaluate and compare these placement strategies in a simulator. Our result shows that the optimized solutions produce lowest service response time and least server utilization in all types of simulated SFCs. On the other hand, the heuristic algorithms are also able to come close to the optimum by simple placing rules.
Schwind, A., Wamser, F., Gensler, T., Seufert, M., Casas, P., Tran-Gia, P.: Streaming Characteristics of Spotify Sessions.The 2nd International Workshop on Quality of Experience Management. , Sardinia, Italy (2018).
Internet Service Providers need a thorough understanding of a service to maximize the Quality of Experience (QoE) of their customers by network management. Instead of quantifying the user satisfaction with long and cost-intensive subjective user studies, the QoE can often be estimated with the help of dedicated measurements of application and network parameters. We designed a QoE measurement tool for the popular audio streaming service Spotify that runs inside a Docker software container. The container is able to run headlessly as active measurement probe and emulates a user who is streaming audio files via Spotify. While streaming, network and application parameters are collected that have a high correlation to the user's QoE. The results of the measurements are used to characterize audio streaming in Spotify on application and network layer, and to evaluate important QoE factors.
Seufert, M., Zeidler, B., Wamser, F., Karagkioules, T., Tsilimantos, D., Loh, F., Tran-Gia, P., Valentin, S.: A Wrapper for Automatic Measurements with YouTube's Native Android App.Network Traffic Measurement and Analysis Conference (TMA). , Wien (2018).
YouTube is one of the most popular and demanding services in the Internet today. Thereby, a large portion of this traffic is generated by YouTube's mobile app. While past studies have shown how to monitor browser-based streaming on desktop PCs (e.g., YoMo) or mobile devices (e.g., YoMoApp), streaming in the native app has not been monitored yet. This paper presents an automated framework for monitoring the streaming in YouTube's native app for Android. The concept is based on a wrapper application and the Android Debug Bridge (adb), and can be also extended to automatic measurements with other apps. For YouTube, it allows to collect application-layer streaming data, such as current playtime, buffered playtime, video encoding, and quality switches. These data can be complemented with network measurements on the mobile access link to obtain a holistic view on mobile YouTube streaming on Android devices. In addition to describing the software design and testbed setup, this paper discusses an experimental measurement. This study analyzes the streaming in the native YouTube app and compares it to the streaming from the mobile YouTube website via YoMoApp.
Grigorjew, A., Lange, S., Zinner, T., Tran-Gia, P.: Performance Benchmarking of Network Function Chain Placement Algorithms.19th International GI/ITG Conference on Measurement, Modelling and Evaluation of Computing Systems (MMB) (2018).
Hirth, M., Lange, S., Seufert, M., Tran-Gia, P.: Performance Evaluation of Mobile Crowdsensing for Event Detection.Proceedings of the 5th International Workshop on Crowd Assisted Sensing, Pervasive Systems and Communications. , Athens, Greece (2018).
Crowdsensing offers a cost effective way to collect large amounts of sensor data. However, in contrast to fixed sensor deployments, the spatial distribution of the sensors can hardly be influence, as the sensors are carried by participants of the crowdsensing system. This in turn raises the question about the performance of such systems with respect to the detection probability and detection time of spatial events. In order to address this question, we analyze the performance of such a crowdsensing system by means of simulation. We use the traffic infrastructure of a small size city in Germany and simulate the inhabitants’ movement patterns with the well established SUMO mobility generator. Our results show that even if only a small share of inhabitants participates in crowdsensing, events, which have locations that are correlated with the population density, can be easily and quickly detected using such a system. On the contrary, events whose locations are uniformly randomly distributed are much harder to detect using a crowdsensing approach.
Loh, F., Burger, V., Wamser, F., Tran-Gia, P., Schembra, G., Rametta, C.: Performance Evaluation of Video Streaming Service Chains in Softwarized 5G Networks with Task Graph Reduction.29th International Teletraffic Congress (ITC) (2017).
Seufert, M., Zach, O., Slanina, M., Tran-Gia, P.: Unperturbed Video Streaming QoE Under Web Page Related Context Factors.9th International Conference on Quality of Multimedia Experience (QoMEX). , Erfurt, Germany (2017).
Quality of Experience (QoE) of Internet services is affected by human, system, and context influence factors. While most QoE studies so far are focused on system factors only, this work will assess the impact of context factors of video streaming on QoE. As video streaming is mostly consumed from web pages, such as video portals, the investigated test conditions are applied to the web page, which embeds the video player. Therefore, the study of context factors is implicitly conducted within a crowdsourced QoE study. The test conditions considered different page load times, poster image qualities, and displayed advertisements on the web page, which are typical context factors when consuming a video streaming service. The results of the study show that the modification of the context factors on the streaming web page leaves the users' QoE rating unperturbed, which suggests that the investigated context factors have a negligible impact on video streaming QoE, or that the rating task of the subjective QoE study superimposed the context factors.
Seufert, M., Kamneng Kwam, B., Wamser, F., Tran-Gia, P.: EdgeNetworkCloudSim: Placement of Service Chains in Edge Clouds Using NetworkCloudSim.1st IEEE International Workshop on Network Programmability - From the Data Center to the Ground (NetFoG). , Bologna, Italy (2017).
Edge cloud computing is a trending paradigm, which extends cloud computing by additionally utilizing computing resources at the network edge, e.g., at mobile base stations. Especially personalized services can be instantiated or migrated close to end users, which improves the latency and supports user mobility. However, the placement of the service chains is crucial for the performance of the services and the energy consumption of the edge cloud platform, and appropriate algorithms have to be designed. To support the simulative performance evaluation of such algorithms, EdgeNetworkCloudSim was developed. It is an extension of NetworkCloudSim, and allows to simulate and evaluate the orchestration and consolidation of service chains in an edge network cloud.
Wamser, F., Höfner, S., Seufert, M., Tran-Gia, P.: Server and Content Selection for MPEG DASH Video Streaming with Client Information.ACM SIGCOMM Workshop on QoE-based Analysis and Management of Data Communication Networks (Internet-QoE). , Los Angeles, CA, USA (2017).
In HTTP adaptive streaming (HAS), such as MPEG DASH, the video is split into chunks and is available in different quality levels. If the video chunks are stored or cached on different servers to deal with the high load in the network and the Quality of Experience (QoE) requirements of the users, the problem of content selection arises. In this paper, we evaluate client-side algorithms for dynamically selecting an appropriate content server during DASH video streaming. We present three algorithms with which the DASH client itself can determine the most appropriate server based on client-specific metrics, like actual latency or bandwidth to the content servers. We evaluate and discuss the proposed algorithms with respect to the resulting DASH streaming behavior in terms of buffer levels and quality level selection.
Schwind, A., Seufert, M., Alay, Ö., Casas, P., Tran-Gia, P., Wamser, F.: Concept and Implementation of Video QoE Measurements in a Mobile Broadband Testbed.IEEE/IFIP Workshop on Mobile Network Measurement (MNM’17). , Dublin, Ireland (2017).
The MONROE testbed enables the objective performance assessment of MBB networks from the end-user perspective, using highly distributed measurements from fixed and mobile nodes. To quantify the performance of MBB networks for popular Internet services from a user-centric perspective, dedicated tools are needed. In this paper we extend the MONROE testbed to the Quality of Experience (QoE) domain, presenting the design and implementation of a QoE-capable measurement tool for YouTube video streaming. The measurement concept is based on emulating a virtual end-user device requesting video streams, which are then monitored at the network and application layers, on the basis of QoE-relevant features. The initial measurements conducted in the MONROE testbed and reported in this paper demonstrate the applicability of the implemented measurement concept.
Lange, S., Grigorjew, A., Zinner, T., Tran-Gia, P., Jarschel, M.: A Multi-Objective Heuristic for the Optimization of Virtual Network Function Chain Placement.29th International Teletraffic Congress (ITC) (2017).
Burger, V., Seufert, M., Zinner, T., Tran-Gia, P.: An Approximation of the Backhaul Bandwidth Aggregation Potential Using a Partial Sharing Scheme.15th IFIP/IEEE International Symposium on Integrated Network Management (IM). , Lisbon, Portugal (2017).
To cope with the increasing demands of mobile devices and the limited capacity of cellular networks, mobile connections are offloaded to WiFi. The access capacity is further increased by aggregating backhaul bandwidth of WiFi access links. To analyze the performance of aggregated access links we develop a model for two and more cooperating systems sharing capacities using an offloading scheme. The state probabilities of the different cooperating systems in the analytic model are determined by a fixed point iterative procedure. By investigating an inner and outer composite system we are able to analyze the system in imbalanced load conditions where the system reaches its full potential utilizing spare bandwidth. To evaluate the robustness of the system against users that try to exploit the system, the bandwidth received by prioritized users is quantified.
Nguyen-Ngoc, A., Lange, S., Zinner, T., Seufert, M., Tran-Gia, P., Aerts, N., Hock, D.: Performance Evaluation of Selective Flow Monitoring in the ONOS Controller.4th International Workshop on Management of SDN and NFV Systems (ManSDN/NFV). , Tokio, Japan (2017).
One of the benefits when network operators adopt the Software Defined Networking (SDN) paradigm is the ability to monitor the traffic in the network without an additional network management system. Usually, SDN controllers utilize OpenFlow statistics messages in order to regularly gather information about all flows in the network. However, using the same polling interval for all flows does not take into account the heterogeneity of real world traffic and thus results in an imbalance between monitoring accuracy and control plane overhead. In particular, frequent querying results in a high resource consumption at the controller. This work proposes a Selective Flow Monitoring (SFM) mechanism that allows administrators to classify flows according to their individual requirements in terms of monitoring frequency, e.g., less frequent polling of elephant flows and frequent polling of QoS sensitive VoIP connections. We compare the performance of the SFM mechanism with the default monitoring scheme in a testbed featuring the Open Network Operating System (ONOS) controller. In this context, the CPU utilization of the controller is used as performance indicator. After identifying relevant influence factors like the number of flows and switches in the network, we investigate the viability of the approaches in different scenarios. Finally, we provide guidelines regarding their choice.
Dinh-Xuan, L., Seufert, M., Wamser, F., Tran-Gia, P.: Study on the Accuracy of QoE Monitoring for HTTP Adaptive Video Streaming Using VNF.1st IFIP/IEEE International Workshop on Quality of Experience Management (QoE-Management). , Lisbon, Portugal (2017).
The fast growth of HTTP video streaming is responsible for a huge amount of traffic over the past few years. Due to the variety and popularity of video content, more and more people are watching videos on the smart TV or on mobile devices. As a result, a potential market is emerging for video providers, which can significantly increase their revenues. In order to offer users a good experience, adaptive video streaming has been introduced to adapt the video quality to the network conditions. Nevertheless, it is still difficult for the network operators to assess the actual video quality on the device of the users and therefore they can not react to improve the service on the network. In this work, we propose a Virtual Network Function (VNF) to monitor the Quality of Experience (QoE) for online video service in the network. To conduct the study, on the one hand, we design a VNF monitoring to measure the video quality and estimate the QoE at the client machine. Our function is placed in two locations nearby and far away from the user to analyze the impact of geographical placement of the VNF on its performance. On the other hand, we set up a local testbed to examine the functional operation and measure the actual video buffer from a client web browser directly to validate the accuracy of the function. Our findings show that with respect to function placement, the VNF has high accuracy in estimating the QoE if it is deployed at the edge network close to the user. However, the VNF does not perform well when it operates far away from the users, e.g., at data centers. These insights help network vendors to more closely monitor the quality of the videos streamed to their customers.
Seufert, M., Wehner, N., Wamser, F., Casas, P., D'Alconzo, A., Tran-Gia, P.: Unsupervised QoE Field Study for Mobile YouTube Video Streaming with YoMoApp.9th International Conference on Quality of Multimedia Experience (QoMEX). , Erfurt, Germany (2017).
YoMoApp (YouTube Monitoring App) is an Android app to monitor mobile YouTube video streaming on both application- and network-layer. Additionally, it allows to collect subjective Quality of Experience (QoE) feedback of end users. During the development of the app, the stable versions of YoMoApp were already available in the Google Play Store, and the app was downloaded, installed, and used on many devices to monitor streaming sessions. As the app was not advertised in special campaigns or used for dedicated QoE studies, the monitored streaming sessions of this period compose the data set of a large unsupervised field study. The collected data set is evaluated to characterize current mobile YouTube streaming on both application and network layers. Furthermore, the problems and methodology to obtain QoE results from such unsupervised field study are discussed together with the actual QoE results. Correlations between QoE factors are investigated, and the QoE of clusters of similar streaming sessions is analyzed.
Gray, N., Lorenz, C., Müssig, A., Gebert, S., Zinner, T., Tran-Gia, P.: A Priori State Synchronization for Fast Failover of Stateful Firewall VNFs.Workshop on Software-Defined Networking and Network Function Virtualization for Flexible Network Management (SDNFlex 2017). , Göttingen, Germany (2017).
Network Functions Virtualization (NFV) replaces physical middleboxes with software instances running network functions in cloud environments. To support this new paradigm, it is necessary to port the code basis from highly specialized hardware devices to virtual machines running on COTS hard- ware. In order to fully exploit the inherent capabilities of cloud environments it is further necessary to redesign the software to support a large amount of distributed, cooperating function instances instead of single, isolated and monolithic instances. This development can be observed for network functions like stateful firewalling. Until now, available software firewalls lack support for active/active operation in clustered environments, which hinders horizontal scalability. This is due to the fact that the required synchronization of connection states among the cluster’s instances is an impediment that still has to be resolved. Therefore, this work investigates different synchronization strategies and mechanisms, which allow to share connection states among the cluster to maintain scalability and high-availability
Iffländer, L., Wamser, F., Metter, C., Tran-Gia, P., Kounev, S.: Performance Assessment of Cloud Migrations from Network and Application Point of View.Proceedings of 9th EAI International Conference on Mobile Networks and Management (MONAMI 2017). , Melbourne, Australia (2017).
Zach, O., Seufert, M., Hirth, M., Slanina, M., Tran-Gia, P.: On Use of Crowdsourcing for H.264/AVC and H.265/HEVC Video Quality Evaluation.Radioelektronika. , Brno, Czech Republic (2017).
Crowdsourcing has become a popular method in the field of video quality evaluation. Gathering the opinion of the users using crowdsourcing is quick and relatively cheap but such a study has to be designed very carefully in order to give relevant results. So far, the majority of the QoE studies using crowdsourcing has been focusing on the performance of H.264/AVC algorithm in different situations (such as encoder settings, stalling effects, etc). Modern video coding methods, however, are only rarely tested using the crowdsourcing approach. We designed a study comparing the performance of both H.264/AVC and H.265/HEVC standards in the crowdsourcing environment. We deal with the possibilities of delivering and presenting the HEVC encoded content to the participants of the crowdsourcing study and potential challenges. Finally, the study was performed using Microworkers platform and gathered results are then compared with three different objective video quality metrics.
Casas, P., D'Alconzo, A., Wamser, F., Seufert, M., Gardlo, B., Schwind, A., Tran-Gia, P., Schatz, R.: Predicting QoE in Cellular Networks using Machine Learning and in-Smartphone Measurements.9th International Conference on Quality of Multimedia Experience (QoMEX). , Erfurt, Germany (2017).
Monitoring the Quality of Experience (QoE) undergone by cellular network customers has become paramount for cellular ISPs, who need to ensure high quality levels to limit customer churn due to quality dissatisfaction. This paper tackles the problem of QoE monitoring, assessment and prediction in cellular networks, relying on end-user device (i.e., smartphone) QoS passive traffic measurements and QoE crowdsourced feedback. We conceive different QoE assessment models based on supervised machine learning techniques, which are capable to predict the QoE experienced by the end user of popular smartphone apps (e.g., YouTube and Facebook), using as input the passive in-device measurements. Using a rich QoE dataset derived from field trials in operational cellular networks, we benchmark the performance of multiple machine learning based predictors, and construct a decision-tree based model which is capable to predict the per-user overall experience and service acceptability with a success rate of 91% and 98% respectively. To the best of our knowledge, this is the first paper using end-user, in-device passive measurements and machine learning models to predict the QoE of smartphone users in operational cellular networks.
Burger, V., Hirth, M., Hoßfeld, T., Tran-Gia, P.: Principles of Information Neutrality and Counter Measures Against Biased Information.Lecture Notes in Informatics: Value-Sensitive Design of Internet-Based Services. , Klagenfurt, Austria (2016).
The Internet serves as ubiquitous, prompt source of information in our society. Due to the giant amount of information, the access to the information relies on information processing mechanisms as implemented in search engines, product recommendation systems, or online social networks. As a result of the engineered preprocessing mechanism, the retrieved information is biased and does not represent a neutral view on the available information, while end-users often are not aware of this bias. In this article, we define the term “Information Neutrality”, review current principles of information processing in the Internet and discuss influence factors hindering Information Neutrality as well as appropriate countermeasures. The main contribution of this article is to raise the awareness of Information Neutrality as an emerging key challenge in the Internet and to potentially consider Information Neutrality as a factor in the value-sensitive design of Internet-based services.
Seufert, M., Hoßfeld, T., Schwind, A., Burger, V., Tran-Gia, P.: Group-based Communication in WhatsApp.1st IFIP Internet of People Workshop (IoP). , Vienna, Austria (2016).
WhatsApp is a very popular mobile messaging application, which dominates today’s mobile communication. Especially the feature of group chats contributes to its success and changes the way people communicate. The group-based communication paradigm is investigated in this work, particularly focusing on the usage of WhatsApp, communication in group chats, and implications on mobile network traffic.
Gray, N., Zinner, T., Gebert, S., Tran-Gia, P.: Simulation Framework for Distributed SDN-Controller Architectures in OMNeT++.8th EAI International Conference on Mobile Networks and Management (MONAMI 2016). , Abu Dhabi, United Arab Emirates (2016).
SDN introduces the seperation of network control and network data plane. The control plane is removed from distributed network entities and logically centralized as the SDN controller. To provide resilience and performance such a logically centralized controller may again be physically distributed. Scenarios featuring distributed controller architectures include data center deployments, where controller instances synchronize states on small distances and delays, or continental WAN deployments with long distances and delays between controllers. The contribution of this paper is an OMNET++ based simulation framework for assessing the performance of distributed SDN controller architectures. Relevant protocols and controller applications are modelled with a high level of detail. Further, an exemplary implementation of two different controller architectures, namely Hyperflow and Kandoo, is included. Initial results based on the provided implementations are presented.
Gebert, S., Müssig, A., Lange, S., Zinner, T., Gray, N., Tran-Gia, P.: Processing Time Comparison of a Hardware-Based Firewall and its Virtualized Counterpart.8th EAI International Conference on Mobile Networks and Management (MONAMI 2016). , Abu Dhabi, United Arab Emirates (2016).
Metter, C., Seufert, M., Wamser, F., Zinner, T., Tran-Gia, P.: Analytic Model for SDN Controller Traffic and Switch Table Occupancy.12th International Conference on Network and Service Management (CNSM). , Best Paper Award, Montreal, Canada (2016).
Software Defined Networking (SDN) is a major paradigm in the field of current communication networks. SDN is used as the basis of many new networks although few performance models are available in the literature, and the majority of performance evaluations are based primarily on practical measurements. To fill this gap, we develop an analytical model to assess SDN control plane traffic as well as the occupancy of the flow table of an SDN switch. The contribution of this work is the formulation of the model for the performance-decisive parameters control-plane traffic and flow table occupancy and the application of the model for different data plane traffic characteristics. In the end, there is a discussion about the setting of time-out values for storing flow entries in the switch flow table depending on the traffic characteristics in the data plane. The trade-off between the signaling traffic in the control plane and the occupancy of the flow table is discussed in order to minimize both.
Dinh-Xuan, L., Seufert, M., Wamser, F., Tran-Gia, P.: QoE Aware Placement of Content in Edge Networks on the Example of a Photo Album Cloud Service.IEEE 6th International Conference on Communications and Electronics (ICCE). , Ha Long, Vietnam (2016).
The paradigm of Software as a Service has gained great achievements in the last decade. By transferring computation and storage to the cloud and migrating services to the edge network, users benefit from using demanding services on lightweight devices. However, the user perceived quality of experience (QoE) for these services is facing the challenges of network impairments and the accessibility of users. Unlike a typical PC-based software, the cloud provides users a location-aware, flexible placement of resource for a cost effective service. The geographical placement of content is therefore one of the key factors that affects the user's satisfaction. The closer the content to the user geographically is, the faster it will be delivered to the user that will also increase the user perceived QoE. In this work, we estimate more precisely the QoE for photo loading time in a particular usage of a photo album cloud service with regard to the influence of various parameters. Firstly, we validate a TCP throughput model and use it to calculate the photo loading time from a given photo size and network QoS. Thereafter, we formulate a mapping function to calculate the MOS value from a QoE model adding the output of the TCP model. From this mapping function, we can estimate QoE for photo loading time from a given photo size, its placement and network QoS. Our main contribution is to determine the trade-off between the size of photo and its placement to acquire a high QoE for photo loading time, which is important for the development of a photo album cloud service.
Wamser, F., Seufert, M., Höfner, S., Tran-Gia, P.: Concept for Client-initiated Selection of Cloud Instances for Improving QoE of Distributed Cloud Services.ACM SIGCOMM Workshop on QoE-based Analysis and Management of Data Communication Networks (Internet-QoE). , Florianópolis, Brazil (2016).
We introduce a concept for client-initiated selection of service location and service quality for improving the Quality of Experience (QoE) of general cloud services. It is loosely based on the HTTP adaptive streaming approach (e.g., MPEG DASH). A manifest file compiled by the cloud service provider specifies the available service locations and qualities, from which the user selects the optimal service instance based on contextual information obtained from client measurements and user preferences. The proposed concept is defined and is implemented in two client-based decision algorithms for improving the QoE of a simple picture gallery cloud service. These decision algorithms are evaluated and their impact on the service delivery is discussed. The evaluation shows that it is possible to improve the service location and quality selection by light-weight client-based algorithms.
Gebert, S., Geissler, S., Zinner, T., Nguyen-Ngoc, A., Lange, S., Tran-Gia, P.: ZOOM: Lightweight SDN-based Elephant Detection.First International Workshop on Programmability for Cloud Networks and Applications (PROCON). , Würzburg, Germany (2016).
Software Defined Networking (SDN) offers a holistic view of the network through a centralized control plane. Consequently, routing decisions can be made based on global knowledge about the network topology as well as its current state. As long living flows are suitable candidates for rerouting, their detection is crucial for efficient flow based traffic management. This work proposes the ZOOM algorithm for elephant detection in SDN networks. To this end, ZOOM follows a very lightweight approach that only uses packet counters implemented by OpenFlow switches and thus does not require any additional hardware. By exploiting this feature of OpenFlow switches, ZOOM allows lightweight and cost-effective elephant detection.
Nguyen-Ngoc, A., Lange, S., Gebert, S., Zinner, T., Tran-Gia, P., Jarschel, M.: Performance Evaluation Mechanisms for FlowMod Message Processing in OpenFlow Switches.IEEE Sixth International Conference on Communications and Electronics. , Ha Long City, Vietnam (2016).
Network operators can benefit in terms of flexibility, cost, and vendor-independence when adopting the Software Defined Networking (SDN) paradigm. In many scenarios, the SDN controller orders the installation of new flow table entries in the switches it manages. Since such operations are handled in the slow path of the switches, the corresponding processing times constitute an important performance indicator for switches. This work focuses on a comparison of two mechanisms for evaluating the performance of OpenFlow switches with respect to the processing time of FlowMod messages. These mechanisms are characterized by different degrees of accuracy, cost, complexity, and the capability of performing measurements at run time. The first mechanism is based on the Spirent C1 dedicated testing platform, while the other uses a software module for the OpenDaylight controller. We assess their capabilities with respect to the abovementioned characteristics and quantify their accuracy by means of wiretaps that provide a ground truth regarding the measured processing times. By using three different switches in the experiments, it is possible to distinguish between hardware specific side-effects and general phenomena.
Burger, V., Frances Pajo, J., Sanchez, O.R., Seufert, M., Schwartz, C., Wamser, F., Davoli, F., Tran-Gia, P.: Load Dynamics of a Multiplayer Online Battle Area and Simulative Assessment of Edge Server Placements.ACM Multimedia Systems Conference (MMSys). , Klagenfurt, Austria (2016).
Free-to-play models, streaming of games and eSports are reasons for online gaming to grow in popularity recently. On the forefront are multiplayer online battle arenas, which gain high popularity by introducing a competitive format that is easy to access and requires cooperation and team play. These games highly rely on fast reaction of the players, which makes latency the key performance indicator of such applications. To obtain low latency, this paper proposes moving game servers close to players towards the edge of the network. The performance of such mechanism highly depends on the geographic distribution of players. By analyzing match histories and statistics, we develop models for the arrival process and location of game requests. This allows us to evaluate the performance of edge server resource migration policies in an event based simulation. Our results show that a high number of edge servers is preferable compared to few larger edge servers to reduce the latency of players. This supports approaches that allow deploying virtual server instances in the back-haul.
Cofano, G., De Cicco, L., Zinner, T., Nguyen-Ngoc, A., Tran-Gia, P., Mascolo, S.: Design and Experimental Evaluation of Network-assisted Strategies for HTTP Adaptive Video Streaming.Best Student Paper Award, ACM Multimedia Systems Conference (MMSys). , Klagenfurt, Austria (2016).
In this paper we investigate several network-assisted streaming approaches which rely on active cooperation between video streaming applications and the network. We build a Video Control Plane which enforces Video Quality Fairness among concurrent video flows generated by heterogeneous client devices. To the purpose, a max-min fairness optimization problem is solved at run-time. We compare two approaches to actuate the optimal solution in an SDN network: the first one allocating network bandwidth slices to video flows, the second one guiding video players in the video bitrate selection. Performance is assessed through several QoE-related metrics, such as Video Quality Fairness, video quality, and switching frequency. The impact of client-side adaptation algorithms is also investigated.
Gebert, S., Zinner, T., Lange, S., Schwartz, C., Tran-Gia, P.: Performance Modeling of Softwarized Network Functions Using Discrete-Time Analysis.28th International Teletraffic Congress (ITC). , Würzburg, Germany (2016).
The softwarization of networks promises cost savings and better scalability of network functions by moving functionality from specialized devices into commercial off-the-shelf hardware. Generalized computing hardware offers many degrees for adjustment and tuning, which can affect performance and resource utilization. One of these adjustments are the interrupt mitigation techniques implemented by modern network interface cards and operating systems. Using these, an administrator can optimize either lower latencies or lower CPU overhead for processing of network traffic. In this work, an analytical model that allows computing relevant performance metrics like the packet processing time and the packet loss for generic virtualized network functions running on commodity hardware is developed. The applicability of the model is shown by comparing its outcome with measurements conducted in a local testbed. Based on this model, impact factors like the average packet interarrival time, the interarrival time distribution, and the duration of the interrupt aggregation interval are studied.
Seufert, M., Zach, O., Hoßfeld, T., Slanina, M., Tran-Gia, P.: Impact of Test Condition Selection in Adaptive Crowdsourcing Studies on Subjective Quality.8th International Conference on Quality of Multimedia Experience (QoMEX). , Lisbon, Portugal (2016).
Adaptive crowdsourcing is a new approach to crowdsourced Quality of Experience (QoE) studies, which aims to improve the certainty of resulting QoE models by adaptively distributing a fixed budget of user ratings to the test conditions. The main idea of the adaptation is to dynamically allocate the next rating to a condition, for which the submitted ratings so far show a low certainty. This paper investigates the effects of statistical adaptation on the distribution of ratings and the goodness of the resulting QoE models. Thereby, it gives methodological advice how to select test conditions for future crowdsourced QoE studies.
Seufert, M., Casas, P., Wamser, F., Wehner, N., Schatz, R., Tran-Gia, P.: Application-Layer Monitoring of QoE Parameters for Mobile YouTube Video Streaming in the Field.IEEE 6th International Conference on Communications and Electronics (ICCE). , Ha Long, Vietnam (2016).
YouTube video streaming is one of the most popular and most demanding services in cellular networks. Thus, operators are concerned about the quality of the streaming delivered by their networks and would like to monitor the Quality of Experience (QoE) of the end users. In this work, we conduct a field study of mobile YouTube video streaming, in which both network flow parameters and application-layer streaming parameters were monitored, and present the characteristics of current mobile YouTube streaming. The impact of both approaches is investigated showing that monitoring network parameters is not sufficient to directly infer the resulting QoE. In contrast, the streaming parameters, which can be obtained from application-layer monitoring, show high correlations to the subjectively experienced quality, and thus, are better suited for QoE monitoring.
Lange, S., Nguyen-Ngoc, A., Gebert, S., Zinner, T., Jarschel, M., Koepsel, A., Sune, M., Raumer, D., Gallenmüller, S., Carle, G., Tran-Gia, P.: Performance Benchmarking of a Software-Based LTE SGW.2nd International Workshop on Management of SDN and NFV Systems. , Barcelona, Spain (2015).
Network Functions Virtualization (NFV) is a concept that aims at providing network operators with benefits in terms of cost, flexibility, and vendor independence by utilizing virtualization techniques to run network functions as software on commercial off-the-shelf (COTS) hardware. In contrast, prior solutions rely on specialized hardware for each function. Performance evaluation of such systems usually requires a dedicated testbed for each individual component. Rather than analyzing these proprietary black-box components, Virtualized Network Functions (VNFs) are pieces of software that run on COTS hardware and whose properties can be investigated in a generic testbed. However, depending on the underlying hardware, operating system, and implementation, VNFs might behave differently. Therefore, mechanisms for the performance evaluation of VNFs should be similar to benchmarking of software, where different implementations are compared by applying them to predefined test cases and scenarios. This work presents a first step towards a benchmarking framework for VNFs. Given two different implementations of a VNF that acts as LTE Serving Gateway (SGW), influence factors and key performance indicators are identified and a comparison between the two mechanisms is drawn.
Burger, V., Kaup, F., Seufert, M., Wichtlhuber, M., Hausheer, D., Tran-Gia, P.: Energy Considerations for WiFi Offloading of Video Streaming.7th EAI International Conference on Mobile Networks and Management (MONAMI). , Santander, Spain (2015).
The load on cellular networks is constantly increasing. Especially video streaming applications, whose demands and requirements keep growing, put high loads on cellular networks. A solution to mitigate the cellular load in urban environments is offloading mobile connections to WiFi access points, which is followed by many providers recently. Because of the large number of mobile users and devices there is also a high potential to save energy by WiFi offloading. In this work, we develop a model to assess the energy consumption of mobile devices during video sessions. We evaluate the potential of WiFi offloading in an urban environment and the implications of offloading connections on energy consumption of mobile devices. Our results show that, although WiFi is more energy efficient than 3G and 4G for equal data rates, the energy consumption increases with the amount of connections offloaded to WiFi, due to poor data rates obtained for WiFi in the streets. This suggests further deployment of WiFi access points or WiFi sharing incentives to increase data rates for WiFi and energy efficiency of mobile access.
Zinner, T., Cofano, G., Wamser, F., De Cicco, L., Mascolo, S., Tran-Gia, P.: Interaction of Control Loops on Application, Transport, and Network Layer.EUCNC - Special Session 3 QoS/QoE Monitoring and Management with SDN. , Paris (2015).
Schwartz, C., Borchert, K., Hirth, M., Tran-Gia, P.: Modeling Crowdsourcing Platforms to Enable Workforce Dimensioning.International Telecommunication Networks and Applications Conference. , Sydney, Australia (2015).
Crowdsourcing platforms provide an easy and scalable access to human workforce that can, e.g., provide subjective judgements, tagging information, or even generate knowledge. In conjunction with machine clouds offering scalable access to computing resources, these human cloud provider offer numerous possibilities for creating new applications which would not have been possible a few years ago. However, in order to build sustainable services on top of this inter-cloud environment, scalability considerations have to be made. While cloud computing systems are already well studied in terms of dimensioning of the hardware resources, there still exists little work on the appropriate scaling of crowdsourcing platforms. This is especially challenging, as the complex interaction between all involved stakeholders, platform providers, workers and employers have to be considered. The contribution of this work is threefold. First we develop a model for common crowdsourcing platforms and implement the model using a simulative approach, which is validated with a comparison to an analytic M[X]/M/c − ∞ system. In a second step we evaluate inter-arrival times as well as campaign size distributions based on a dataset of a large commercial crowdsourcing platform to derive realistic model parameters and illustrate the differences to the analytic approximation. Finally, we perform a parameter study using the simulation model to derive guidelines for dimensioning crowdsourcing platforms, while considering relevant parameters for the involved stakeholders, i.e., the delay before work on a task begins and the work load of the workers.
Metter, C., Gebert, S., Lange, S., Zinner, T., Tran-Gia, P., Jarschel, M.: Investigating the Impact of Network Topology on the Processing Times of SDN Controllers.Seventh IFIP/IEEE International Workshop on Management of the Future Internet. , Ottawa, Canada (2015).
Software Defined Networking (SDN) introduces the concept of logically-centralized controllers in charge of managing the forwarding behavior of network elements. The new possibilities enabled through the centralization of control logic come with a certain risk: The controller might become a performance bottleneck. Therefore, ensuring sufficient controller performance is one of the crucial tasks prior to a successful SDN deployment. Furthermore, fine-grained traffic engineering, e.g., to achieve higher link utilization, results in a higher frequency of requests that are sent to the controller, which leads to an increased controller load. It is therefore important to analyze the capabilities of SDN controllers prior to deployment. This paper investigates two software implementations, the OpenDaylight and Ryu controllers. The control message throughput of different controllers has been studied several times already; however, it is not yet known what influence the number and topology of connected switches have. This paper investigates this influence in detail for a fat-tree data center topology and a WAN topology as well as 261 topologies with varying characteristics from the Internet Topology Zoo.
Burger, V., Seufert, M., Kaup, F., Wichtlhuber, M., Hausheer, D., Tran-Gia, P.: Impact of WiFi Offloading on Video Streaming QoE in Urban Environments.IEEE Workshop on Quality of Experience-based Management for Future Internet Applications and Services (QoE-FI). , London, UK (2015).
Video streaming is the most popular application in today's mobile Internet and its growing demands and popularity put more and more load on cellular networks. In a recent trend to mitigate the cellular load, followed by many providers, users are offered to offload mobile connections to WiFi hotspots, which are predominately deployed in urban environments. In this work, we conduct a simulative performance evaluation of the impact of WiFi offloading on the Quality of Experience (QoE) of video streaming. The evaluation is based on connectivity measurements from a German city and uses a simple QoE model for estimating the perceived quality of video streaming. Our findings show that, despite its benefits for operators, offloading to WiFi has a negative impact on video streaming QoE for some users when 3G/4G coverage is available. Only in the case of 2G coverage, WiFi offloading can significantly improve the perceived quality for users.
Gebert, S., Jarschel, M., Herrnleben, S., Zinner, T., Tran-Gia, P.: TableVisor: An Emulation Layer for Multi-Table OpenFlow Switches.4th European Workshop on Software Defined Networks (EWSDN). , Bilbao, Spain (2015).
This demonstration introduces TableVisor, which acts as a proxy layer between an OpenFlow controller and switches. Multiple hardware switches connect to TableVisor before it establishes a connection with the OpenFlow controller instance. During connection establishment, TableVisor advertises in the answer to the controller's features-request that this switch comprises a certain number of tables, which actually reflects the number of connected switches. All communication between controller and switch is passed through the proxy layer. Depending on the type of message, it will be answered directly by TableVisor (hello, features-reply), modified in such a way that particular fields are rewritten (packet-in, flow-mod), or a response merging data from multiple switches will be returned (flow-stats). The demonstration shows TableVisor in a MPLS use case using multiple switches, which is motivated by a mobile network scenario.
Lange, S., Gebert, S., Spoerhase, J., Rygielski, P., Zinner, T., Kounev, S., Tran-Gia, P.: Specialized Heuristics for the Controller Placement Problem in Large Scale SDN Networks.International Teletraffic Congress (ITC 27). , Ghent, Belgium (2015).
The Software Defined Networking~(SDN) concept introduces a paradigm shift in the networking world towards an externalized control plane which is logically centralized. When designing an SDN-based WAN architecture, it is of vital importance to find a feasible solution to the controller placement problem, i.e., to decide where to position a limited amount of resources within the network. In addition to time-independent constraints regarding aspects like scalability, resilience, and control plane communication delays, dynamically changing network conditions like traffic patterns or bandwidth demands need to be considered as well. Consequently, such dynamic environments call for a regular and fast recalculation of placements in order to adapt to the current situation in a timely manner. While an exhaustive evaluation of all possible solutions can be performed within a practically feasible time frame for small and medium-sized networks, such an approach is out of scope for large problem instances which have significantly higher time and memory requirements. Therefore, this work investigates a specialized heuristic, which takes into account a particular set of optimization objectives and returns solutions representing the possible trade-offs between them. Due to its low computation time and acceptable margin of error, this heuristic can be employed by automatic decision systems operating in dynamic environments.
Gebert, S., Schwartz, C., Zinner, T., Tran-Gia, P.: Continuously Delivering Your Network (Short Paper).IEEE/IFIP International Symposium on Integrated Network Management (IM). , Ottawa, Canada (2015).
Softwarization and cloudification of networks through software defined networking and network functions virtualisation promise a new degree of flexibility and agility. By moving logic from device firmware into software applications and applying software development mechanisms, innovation can be introduced with less effort. Concrete ways how to operate and orchestrate such systems are not yet defined. The process of making changes to a controller software or a virtualized network function in a production network without the risk of network disruption is not covered by literature. Complexity of systems brings the risk of unexpected side-effects and has so long been a show-stopper for administrators applying changes to networking devices. This paper suggests the adaption of the successful concept of continuous delivery into the software defined networking world. Test-driven development and automatic acceptance tests demonstrate that the software engineering community already found ways to ensure that changes do not break. Applied to network engineering, the adaption of continuous delivery can be seen as an enabler for risk-free and frequent changes in production infrastructure through push button deployments.
Seufert, M., Burger, V., Wamser, F., Tran-Gia, P., Moldovan, C., Hoßfeld, T.: Utilizing Home Router Caches to Augment CDNs towards Information-Centric Networking.European Conference on Networks and Communications (EuCNC). , Paris, France (2015).
To implement improved Quality of Service (QoS) and Quality of Experience (QoE) management for content-heavy services like video streaming, content has to be moved closer to the edge. The concept of information-centric networking (ICN) would be a prospective enabler but is currently not practically feasible yet. We propose a hierarchical caching architecture utilizing caches on home routers to augment existing content delivery network (CDN) infrastructure. This approach can be implemented via Software-defined Networking (SDN) and brings current CDNs closer towards ICN. Based on a simulation study, we confirm that our approach is able to serve content more locally, which results in QoS and QoE benefits for end users as well as inter-domain traffic savings for network operators.
Nguyen-Ngoc, A., Lange, S., Gebert, S., Zinner, T., Tran-Gia, P., Jarschel, M.: Investigating Isolation between Virtual Networks in Case of Congestion for a Pronto 3290 Switch.Workshop on Software-Defined Networking and Network Function Virtualization for Flexible Network Management (SDNFlex 2015). , Cottbus, Germany (2015).
Resource isolation between virtual networks is one of the key features of network virtualization. It is typically realized by configuring queues with specific rate guarantees on the egress ports of the network devices. The drawback of this architectural choice, however, is that traffic from several ingress ports may result in congestion on an egress port. Hence, the question arises to which extent isolation between virtual networks is realized in state-of-the-art hardware. This work aims at investigating whether congestion within one virtual network may affect the throughput performance of another virtual network. For that, measurements in a local testbed using a Pronto 3290 switch running an OpenFlow-enabling Pica8 firmware are performed.
Schnitzer, S., Rensing, C., Schmidt, S., Borchert, K., Hirth, M., Tran-Gia, P.: Demands on Task Recommendation in Crowdsourcing Platforms - The Worker’s Perspective.CrowdRec Workshop. , Vienna, Austria (2015).
Crowdsourcing platforms support the assignment of jobs to help requesters in their project completion and allow workers to earn money. Most crowdsourcing platforms apply simple schemes in order to filter the tasks a worker can choose from or rely on the workers’ search capabilities. Using genuine task recommendation within such crowdsourcing plat- forms opens promising opportunities. Such recommendation schemes will only be effective if the workers are confident that they are used towards their own good. In order to gain insights on what kind of recommendations the workers would expect and accept, this work provides an empirical study about the demands of the workers.
Becker, M., Borchert, K., Hirth, M., Mewes, H., Hotho, A., Tran-Gia, P.: MicroTrails: Comparing Hypotheses about Task Selection on a Crowd Sourcing Platform.International Conference on Knowledge Technologies and Data-driven Business (I-KNOW). , Graz, Austria (2015).
To optimize the workflow on commercial crowdsourcing platforms like Amazon Mechanical Turk or Microworkers, it is important to understand how users choose their tasks. Current work usually explores the underlying processes by employing user studies based on surveys with a limited set of participants. In contrast, we formulate hypotheses based on the different findings in these studies and, in- stead of verifying them based on user feedback, we compare them directly on data from a commercial crowdsourcing platform. For evaluation, we use a Bayesian approach called HypTrails which allows us to give a relative ranking of the corresponding hypotheses. The hypotheses considered, are for example based on task categories, monetary incentives or semantic similarity of task descriptions. We find that, in our scenario, hypotheses based on employers as well the the task descriptions work best. Overall, we objectively compare different factors influencing users when choosing their tasks. Our approach enables crowdsourcing companies to better understand their users in order to optimize their platforms, e.g., by incorporating the gained knowledge about these factors into task recommendation systems.
Seufert, M., Wamser, F., Casas, P., Irmer, R., Tran-Gia, P., Schatz, R.: YouTube QoE on Mobile Devices: Subjective Analysis of Classical vs. Adaptive Video Streaming.6th International Workshop on Traffic Analysis and Characterization (TRAC). , Dubrovnik, Croatia (2015).
YouTube is the most popular service in the Internet and is increasingly consumed on mobile devices. With emerging adaptive video streaming technology, the question arises whether it should be also employed in the mobile context, which shows different characteristics in terms of display sizes and reliability of Internet connection. This paper compares YouTube QoE on mobile devices for both classical and adaptive video streaming based on a subjective lab experiment, in which different network conditions were emulated. Our results show that adaptive video streaming provides almost excellent results for the poorest network conditions. Thereby, it clearly outperforms classical video streaming, and thus, should be considered to achieve higher QoE in future mobile streaming applications.
Seufert, M., Schwind, A., Hoßfeld, T., Tran-Gia, P.: Analysis of Group-based Communication in WhatsApp.7th EAI International Conference on Mobile Networks and Management (MONAMI). , Santander, Spain (2015).
This work investigates group-based communication in WhatsApp based on a survey and the analysis of messaging logs. The characteristics of WhatsApp group chats in terms of usage and topics are outlined. We present a classification based on the topic of the group and classify anonymized messaging logs based on message statistics. Finally, we model WhatsApp group communication with a semi-Markov process, which can be used to generate network traffic similar to real messaging logs.
Wamser, F., Seufert, M., Casas, P., Irmer, R., Tran-Gia, P., Schatz, R.: YoMoApp: a Tool for Analyzing QoE of YouTube HTTP Adaptive Streaming in Mobile Networks.European Conference on Networks and Communications (EuCNC). , Paris, France (2015).
The performance of YouTube in mobile networks is crucial to network operators, who try to find a trade-off between cost-efficient handling of the huge traffic amounts and high perceived end-user Quality of Experience (QoE). This paper introduces YoMoApp (YouTube Performance Monitoring Application), an Android application, which passively monitors key performance indicators (KPIs) of YouTube adaptive video streaming on end-user smartphones. The monitored KPIs (i.e., player state/events, buffer, and video quality level) can be used to analyze the QoE of mobile YouTube video sessions. YoMoApp is a valuable tool to assess the performance of mobile networks with respect to YouTube traffic, as well as to develop optimizations and QoE models for mobile HTTP adaptive streaming. We test YoMoApp through real subjective QoE tests showing that the tool is accurate to capture the experience of end-users watching YouTube on smartphones.
Jarschel, M., Metter, C., Zinner, T., Gebert, S., Tran-Gia, P.: OFCProbe: A Platform-Independent Tool for OpenFlow Controller Analysis.5th IEEE International Conference on Communications and Electronics (IEEE ICCE 2014). , Da Nang, Vietnam (2014).
Controller performance and behavior are key to the operation of an SDN network. Therefore, choosing the right controller implementation and corresponding set of applications is essential. In order to facilitate this decision we previously introduced a tool for controller performance analysis called ”OFCBenchmark”. In this paper, we present ”OFCProbe” a platform-independent and extended re-design of our original approach. We describe the new architecture and explain the implemented features. Finally, we provide some sample results to illustrate the kind of investigations that can be performed using the tool.
Wamser, F., Iffländer, L., Zinner, T., Tran-Gia, P.: Implementing Application-Aware Resource Allocation on a Home Gateway for the Example of YouTube.Mobile Networks and Management, Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering. , Würzburg, Germany (2014).
Today’s Internet does not offer any quality level beyond best effort for the majority of applications used by private customers. If multiple customers with heterogeneous applications share a bottleneck link to the Internet, this often leads to quality deterioration for the customers. This particularly holds for home networks with smallband Internet access and for home networks with resource limitation like a bad channel quality within a wireless network. For such cases, the best effort allocation of resources between heterogeneous applications leads to an unfair distribution of the application quality among the users. To provide a similar application quality for all users, we propose to implement an application-oriented resource management on a home gateway. Therefore, allocation mechanisms need to be implemented such as the prioritization of network flows. Furthermore, a component monitoring the application quality and dynamically triggering these mechanisms is required. We show the feasibility of this concept by the implementation of an application monitor for YouTube on a standard home gateway. The gateway estimates the YouTube video buffers and prioritizes the video clip before the playback buffer depletes.
Hirth, M., Scheuring, S., Hoßfeld, T., Schwartz, C., Tran-Gia, P.: Predicting Result Quality in Crowdsourcing Using Application Layer Monitoring.5th International Conference on Communications and Electronics (ICCE 2014). , Da Nang, Vietnam (2014).
Crowdsourcing has become a valuable tool for many business applications requiring to meet a certain quality of the results generated by the workers. Therefore, several quality assurance mechanisms have been developed which are partly deployed in commercial crowdsourcing platforms. However, these mechanisms usually impose additional work overhead for the worker, e.g. by adding test questions, or increase the costs for the employer, e.g. by replicating the task for majority decisions. In this work, we analyze the applicability of implicit measurements to objectively estimate the quality of the workers' results. First efforts in this area have already been made by investigating the impact of the task completion time. We extend this research by deploying an application layer monitoring (ALM), which enables monitoring the workers' interactions with our task interface on a much more detailed level. Based on an exemplary use case, we discuss a possible implementation and demonstrate the potential of the approach by predicting the quality of the workers' submission based on our monitoring results. This ALM provides a new way to identify low quality work as well as difficulties in fulfilling the formulated tasks in the domain of Crowdsourcing.
Schwartz, C., Hirth, M., Hoßfeld, T., Tran-Gia, P.: Performance Model for Waiting Times in Cloud File Synchronization Services.26th International Teletraffic Congress (ITC). , Karlskrona, Sweden (2014).
Over the last few years, the importance of cloud services for file synchronization has been increasing. With the release of network enabled cameras like Google Glass the trend of synchronizing new photos with the cloud has emerged as an important new use case for mobile networks. Multiple stakeholder are interested in optimizing this synchronization process according to different orthogonal metrics. The end user is interested in a fast synchronization of images as well as a low energy consumption of the client used for upload to the network. The network operator requires a low number of network connections per synchronization of a batch of images in order to reduce the signaling load of the mobile network. This paper answers the question if the goals of the stakeholders can be achieved by selecting an appropriate synchronization scheduling mechanism. Therefore, we first present a model for the waiting time of cloud file synchronization services. Second, we perform measurements on the popular Dropbox service to obtain parameters required in the model. Finally, we perform a parameter study over the considered mechanisms and parameters, suggest a preferable algorithm and identify trade-offs favorable for all stakeholders.
Gebert, S., Hock, D., Hartmann, M., Spoerhase, J., Zinner, T., Tran-Gia, P.: Including Energy Efficiency Aspects in Multi-Layer Optical Network Design.5th International Conference on Communications and Electronics (ICCE 2014). , Da Nang, Vietnam (2014).
This paper investigates the influence of the network planning process on a higher energy-awareness of optical multi-layer core networks. In particular, we propose to remove redundant links in the network, and to route corresponding network traffic on other links. Based on the reduced network topology, we compute the required network equipment for realistic traffic demands using a network planning tool. Due to the lack of an accurate model for operational expenditures and energy consumption, we choose the link length as cost function. We show the applicability of our idea and demonstrate the energy saving potential using realistic network topologies.
Wamser, F., Zinner, T., Z Zhu, J., Tran-Gia, P.: Dynamic Bandwidth Allocation for Multiple Network Connections: Improving User QoE and Network Usage of YouTube in Mobile Broadband.ACM SIGCOMM Capacity Sharing Workshop (CSWS 2014). , Chicago, IL, USA (2014).
Schwartz, C., Scheib, M., Hoßfeld, T., Tran-Gia, P., Manuel Gimenez-Guzman, J.: Trade-Offs for Video-Providers in LTE Networks: Smartphone Energy Consumption Vs Wasted Traffic.22nd International Teletraffic Congress Specialist Seminar on Energy Efficient and Green Networking. , Christchurch, New Zealand (2013).
Long Term Evolution (LTE) networks provide broadband Internet access to mobile users. One of the main use cases for LTE is a mobile video. When selecting a video transmis- sion mechanism, a video provider has to consider different and orthogonal metrics. The consumer expects a high video Quality of Experience (QoE) and a low energy consumption during download and playback. The video provider is interested in minimizing its resources and corresponding costs, like bandwidth and wasted traffic. Wasted traffic occurs if a user aborts and additional video data is already downloaded but not played out, consuming resources unnecessarily. This raises the questions 1) how a video provider delivers the video contents while reducing the operational costs and satisfying the customers demands 2) what is the influence of the customer abort behaviour. To answer these questions, we first study the influence of mechanism selection on energy consumption and wasted traffic. Second, we show that the different user models do not influence the wasted traffic significantly. Finally, we provide parameter se- lection guidelines for the Streaming mechanism, which are shown to satisfy better both the requirements of the video provider as well as those of the customer, to achieve Pareto optimal results with regard to the smartphone energy consumption and wasted traffic.
Hock, D., Hartmann, M., Gebert, S., Jarschel, M., Zinner, T., Tran-Gia, P.: Pareto-Optimal Resilient Controller Placement in SDN-based Core Networks.25th International Teletraffic Congress (ITC). , Shanghai, China (2013).
With the introduction of Software Defined Networking (SDN), the concept of an external and optionally centralized network control plane, i.e. controller, is drawing the attention of researchers and industry. A particularly important task in the SDN context is the placement of such external resources in the network. In this paper, we discuss important aspects of the controller placement problem with a focus on SDN-based core networks, including different types of resilience and failure tolerance. When several performance and resilience metrics are considered, there is usually no single best controller placement solution, but a trade-off between these metrics. We introduce our framework for resilient Pareto-based Optimal COntroller-placement (POCO) that provides the operator of a network with all Pareto-optimal placements. The ideas and mechanisms are illustrated using the Internet2 OS3E topology and further evaluated on more than 140 topologies of the Topology Zoo. In particular, our findings reveal that for most of the topologies more than 20% of all nodes need to be controllers to assure a continuous connection of all nodes to one of the controllers in any arbitrary double link or node failure scenario.
Jarschel, M., Wamser, F., Höhn, T., Zinner, T., Tran-Gia, P.: SDN-based Application-Aware Networking on the Example of YouTube Video Streaming.2nd European Workshop on Software Defined Networks (EWSDN 2013). , Berlin, Germany (2013).
Application-Aware Networking is a promising approach to provide good application quality to users in scenarios with limited network resources, like today’s access networks. With SDN, a particularly interesting method to enable flowbased traffic management in networks has become available. In this work we take a look at how a specific application, i.e., YouTube Streaming, can benefit from such an SDN-based Application-Aware Network. We implement and investigate an approach based on Deep Packet Inspection (DPI) and one based on direct information input from the application in an OpenFlow testbed in order to show, how these different types of application information can be exploited to enhance the Quality of Experience (QoE). Furthermore, we determine the overhead caused by each of the presented approaches.
Wamser, F., Deschner, S., Zinner, T., Tran-Gia, P.: Investigation of Different Approaches for QoE-Oriented Scheduling in OFDMA Networks.Mobile Networks and Management, Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering Volume 125. pp. 172-187. , Cork, Irland (2013).
QoE- and application-aware scheduling is a new paradigm for mobile communication networks. It aims at making better use of network resources with respect to the perceived quality of the users. To achieve this, it specifies an interaction between application and networking layers. Previous work has shown that such a resource management is possible by the weighting of applications and the definition of key quality indicators. However, quantification of the benefits and the impact on the application itself is hardly studied, since it requires precise modeling of both the data transmission in the mobile network as well as the application itself. In this paper the influence of different cross-layer scheduling heuristics on the application is examined for the air interface of LTE mobile networks. For this, not only the physical data transmission but also the application behavior is simulated in detail for Skype, YouTube, web browsing, and downloads. For each application quality indicators are defined that provide information on the current performance of the application. The investigated scheduling approaches take into account detailed application information of different levels like the application type, the current status of the application, or the ability of an application to adapt to the network situation.
Hinrichsen, H., Hoßfeld, T., Hirth, M., Tran-Gia, P.: Entropy Production in Stationary Social Networks.4th Workshop on Complex Networks (CompleNet 2013). , Berlin, Germany (2013).
Completing their initial phase of rapid growth social networks are expected to reach a plateau from where on they are in a statistically stationary state. Such stationary conditions may have different dynamical properties. For example, if each message in a network is followed by a reply in opposite direction, the dynamics is locally balanced. Otherwise, if messages are ignored or forwarded to a different user, one may reach a stationary state with a directed flow of information. To distinguish between the two situations, we propose a quantity called *entropy production* that was introduced in statistical physics as a measure for non-vanishing probability currents in nonequilibrium stationary states. The proposed quantity closes a gap for characterizing social networks. As major contribution, we present a general scheme that allows one to measure the entropy production in arbitrary social networks in which individuals are interacting with each other, e.g. by exchanging messages. The scheme is then applied for a specific example of the R mailing list.
Schwartz, C., Lehrieder, F., Wamser, F., Hoßfeld, T., Tran-Gia, P.: Smart-Phone Energy Consumption Vs. 3G Signaling Load: The Influence of Application Traffic Patterns.Tyrrhenian International Workshop 2013 on Digital Communications: Green ICT. , Genova, Italy (2013).
The high signaling load in today’s UMTS networks has recently lead to severe problems and network outages of several hours, so called Signaling Storms. The reason is that cer- tain network access patterns of popular smart-phone applications trigger frequent connection re-establishments, which are signaled to the network via the radio resource control (RRC) protocol. As a consequence of the network agnostic implementation of smart- phone applications, entities of the mobile network operator may experience overload, while energy consumption at the smart- phones is mutually determined. The aim of this work is to study the impact of traffic charac- teristics on the power consumption of the smart-phone and the signaling messages in the mobile network. For that purpose, we first develop a simple model for the RRC states of a smart-phone. Second, we estimate the resulting power drain and the signalling traffic of the smart-phone. Then, we investigate the applicability of our model by comparing analytical with simulation results for real-world smart-phone traffic measurements. Finally, we evaluate the effect of network parameter optimization on traffic with different statistical characteristics. Our counter-intuitive results show that in particular bursty traffic patterns are suitable for UMTS networks while periodic patterns may cause increased power consumption and signaling overload – in contrast to classical queueing systems.
Blenk, A., Wamser, F., Zinner, T., Kellerer, W., Tran-Gia, P.: Dynamic HTTP Download Scheduling with Respect to Energy Consumption.24th Tyrrhenian International Workshop on Digital Communications (TIWDC). , Genoa, Italy (2013).
Mobile devices, in particular smartphones, are battery powered. As their small size limits their energy capacity, an intelligent and energy-saving use of resources is crucial for the mobile user experience. Especially energy saving while sending and receiving data becomes important due to the always-on nature of smartphones. One solution for a sophisticated resource usage in wireless access networks is to tailor resource management to applications. The advantage of such mechanisms is to be able to address both the perceived quality of the users and the energy consumption of mobile devices at the same time. We propose several traffic scheduling algorithms for HTTP file download in wireless networks based on this application-aware paradigm. The core idea is to use download scheduling that avoids parallel transmissions and, in contrast, favors sequential transmission. We have implemented and measured the algorithms in a wireless mesh network. The evaluation results quantify the gain of an application-aware resource management with respect to quality of experience and energy consumption.
Sieber, C., Hoßfeld, T., Zinner, T., Tran-Gia, P., Timmerer, C.: Implementation and User-centric Comparison of a Novel Adaptation Logic for DASH with SVC.IFIP/IEEE International Workshop on Quality of Experience Centric Management (QCMan), Best Paper Award. , Ghent, Belgium (2013).
The MPEG-DASH standard allows the client-centric access to different representations of video content via the HTTP protocol. The client can flexibly switch between different qualities, i.e., different bit rates and thus avoid waiting times during the video playback due to empty playback buffers. However, quality switches and the playback of lower qualities is perceived by the user which may reduce the Quality of Experience (QoE). Therefore, novel algorithms are required which manage the streaming behavior with respect to the user's requirements and which do not waste network resources. As indicated by recent studies, scalable video coding (SVC) may use the current network and content distribution infrastructure in a more efficient way than with single layer codecs. The contribution of this paper is the design and the implementation of a novel DASH/SVC streaming algorithm. By means of measurements in a test-bed, its performance and benefits are evaluated and compared to existing algorithms from an user-centric view point with objective performance metrics. Our findings show that the proposed algorithm outperforms other DASH mechanisms in terms of video quality, low switching frequency and usage of the available resources in a realistic mobile network scenario. This is a first step towards true QoE management of video streaming in the Internet with DASH and SVC.
Jarschel, M., Zinner, T., Höhn, T., Tran-Gia, P.: On the Accuracy of Leveraging SDN for Passive Network Measurements.Australasian Telecommunication Networks & Applications Conference (ATNAC 2013). , Christchurch, New Zealand (2013).
Network Measurement has emerged as one promising field of application for Software Defined Networking. The reason for this is that the logically centralized control plane of an SDN network inherently has to aggregate network state information in order to function. This circumstance can be leveraged for network measurements at the SDN controller without the need for additional equipment or active – and possibly disruptive – measurements in the network itself. However, the accuracy and potential resource overhead of this approach has not been discussed. In this paper we compare an SDN-based solution to actual traffic measurements in order to determine its accuracy and resource demand by performing tests in an OpenFlow testbed.
Wamser, F., Staehle, D., Prokopec, J., Mäder, A., Tran-Gia, P.: Utilizing Buffered YouTube Playtime for QoE-oriented Scheduling in OFDMA Networks.International Teletraffic Congress (ITC). , Kraków, Poland (2012).
With the introduction of 4th generation mobile networks, applications such as high-quality video streaming to the end user becomes possible. However, the expected demand for such services outpaces the capacity increase of the networks. Since there is mostly a capacity bottleneck in the air interface between a base station and user equipment, one of the main challenges for radio resource management is therefore to enforce precise quality guarantees for users with high expectations on service quality. We consider, in this paper, an OFDMA access network with YouTube users, and address the challenge of improving the quality of experience (QoE) of a dedicated user by utilizing the buffered playtime of a YouTube video for scheduling. The advantage of this approach is that scheduling is done according to the instantaneous throughput requirement of the end user application, and not by the network by maintaining average quality-of-service (QoS) parameters. The paper describes the concept and provides a simulative evaluation of the approach in an LTE network to demonstrate the benefits.
Hirth, M., Lehrieder, F., Oberste-Vorth, S., Hoßfeld, T., Tran-Gia, P.: Wikipedia and its Network of Authors from a Social Network Perspective.International Conference on Communications and Electronics (ICCE). , Hue, Vietnam (2012).
Online social networks (OSNs) become more and more important in today's social and business life. Therefore, considerable effort is put in research to gain a deeper knowledge of the development of these networks and their dynamics. However, most of the existing literature is based on very limited subsets of the network data, which is often filtered by the OSN operator providing the data or biased by the crawling mechanisms used to obtain the data. This makes it difficult to analyze the temporal evolution of OSNs based on complete data. To overcome this issue, we investigate the dynamics of the publicly available collaboration network of the Wikipedia authors as an example for an OSN-like network. In particular, we study the temporal evolution of this network since its beginning and demonstrate that it exhibits prominent similarities to well known social networks such as the small-world phenomenon. This indicates that the insights gained from the analysis of Wikipedia's collaboration network might be transferable to social networks in general.
Wamser, F., Hock, D., Seufert, M., Pries, R., Tran-Gia, P.: Performance Optimization in Access Networks Using a Combined Control Strategy.12th Würzburg Workshop on IP: ITG Workshop 'Visions of Future Generation Networks' (Euroview). , Würzburg, Germany (2012).
Schwartz, C., Pries, R., Tran-Gia, P.: A Queuing Analysis of an Energy-Saving Mechanism in Data Centers.International Conference on Information Networking (ICOIN). , Bali, Indonesia (2012).
The high energy costs for running a data center led to a rethinking towards an energy-efficient operation of a data center. Designed for supporting the expected peak traffic load, the goal of the data center provider such as Amazon or Google is now to dynamically adapt the number of offered resources according to the current traffic load. In this paper, we present a queuing theoretical model to evaluate the trade-off between waiting time and power consumption if only a subset of servers is active all the time and the remaining servers are enabled on demand. We develop a queuing model with thresholds to turn-on reserve servers when needed. Furthermore, the resulting system behavior under varying parameters and requirements for Pareto optimality are studied.
Pries, R., Magyari, Z., Tran-Gia, P.: An HTTP Web Traffic Model Based on the Top One Million Visited Web Pages.8th Euro-NF Conference on Next Generation Internet. , Karlskrona, Sweden (2012).
Hock, D., Bernardo, V., Zinner, T., Wamser, F., Hummel, K.A., Curado, M., Pries, R., Braun, T., Tran-Gia, P.: Evaluating the Trade-Off Between Energy-Efficiency and QoE in Wireless Mesh Networks.4th International Conference on Communications and Electronics (ICCE 12). , Hué, Vietnam (2012).
Jarschel, M., Oechsner, S., Schlosser, D., Pries, R., Goll, S., Tran-Gia, P.: Modeling and Performance Evaluation of an OpenFlow Architecture.23rd International Teletraffic Congress (ITC 2011). , San Francisco, CA, USA (2011).
The OpenFlow concept of flow-based forwarding and separation of the control plane from the data plane provides a new flexibility in network innovation. While initially used solely in the research domain, OpenFlow is now finding its way into commercial applications. However, this creates new challenges, as questions of OpenFlow scalability and performance have not yet been answered. This paper is a first step towards that goal. Based on measurements of switching times of current OpenFlow hardware, we derive a basic model for the forwarding speed and blocking probability of an OpenFlow switch combined with an OpenFlow controller and validate it using a simulation. This model can be used to estimate the packet sojourn time and the probability of lost packets in such a system and can give hints to developers and researchers on questions how an OpenFlow architecture will perform given certain parameters.
Hoßfeld, T., Hirth, M., Tran-Gia, P.: Modeling of Crowdsourcing Platforms and Granularity of Work Organization in Future Internet.International Teletraffic Congress (ITC). , San Francisco, USA (2011).
Beside of social media networks, crowdsourcing is one of the emerging new applications and business models in the Future Internet, which can dramatically change the future of work and work organization in the on-line world. The crowdsourcing technology can be viewed as “Human Cloud” technique, in contrast to “Machine Cloud Computing”. Using a crowd with a large number of internationally widespread workers and the flexibility of micro-payment services, crowdsourcing platforms like Amazon’s MTurk and Microworkers can outsource traditional forms of work organization on a microscopic level of granularity to a large, anonymous crowd of workers, the human cloud. In such platforms work or tasks are organized at a finer granularity and jobs are split into micro-tasks that need to be performed by a human cloud. It is a need of analysis to understand the anatomy of such a platform and of models to describe the time-dependent growth of the human cloud, in order to predict the traffic impact of such novel applications and to forecast the growth dynamics. The purpose of this paper is a measurement-based statistical analysis of a crowdsourcing platform, using the Microworkers.com platform as example. The obtained results are then used to model the growth of such fast-changing environments in the Internet using well-known models from biology. Based on the findings from the population growth, we develop a deterministic fluid model which is an extension of the SIR model of epidemics, in order to investigate the platform dynamics.
Hirth, M., Hoßfeld, T., Tran-Gia, P.: Cost-Optimal Validation Mechanisms and Cheat-Detection for Crowdsourcing Platforms.Workshop on Future Internet and Next Generation Networks (FINGNet). , Seoul, Korea (2011).
Crowdsourcing is becoming more and more important for commercial purposes. With the growth of crowdsourcing platforms like MTurk or Microworkers, a huge work force and a large knowledge base can be easily accessed and utilized. But due to the anonymity of the workers, they are encouraged to cheat the employers in order to maximize their income. Thus, this paper presents two crowd-based approaches to validate the submitted work. Both approaches are evaluated with regard to their detection quality, their costs and their applicability to different types of typical crowdsourcing tasks.
Klein, D., Menth, M., Pries, R., Tran-Gia, P., Scharf, M., Söllner, M.: A Subscription Model for Time-Scheduled Data Transfers.12th IFIP/IEEE International Symposium on Integrated Network Management (IM 2011). , Dublin, Ireland (2011).
We recently witness new services that can afford some delay until data transmission starts, but then benefit from a very large available bandwidth. A popular example is the migration of virtual machines between different sites of a geographically dispersed service provider. In this paper, we propose a subscription model for time-scheduled data transfers. Transmission requests are served consecutively, giving the flows access to the physical bandwidth. This is in contrast to today's Internet where flows are served in parallel so that they compete for the available bandwidth. We present the architecture to enable such data beams. Furthermore, we model and analyze the performance under different conditions and compare it with concurrent transmission.
Schwerdel, D., Hock, D., Günther, D., Reuther, B., Müller, P., Tran-Gia, P.: ToMaTo - a network experimentation tool.7th International ICST Conference on Testbeds and Research Infrastructures for the Development of Networks and Communities (TridentCom 2011). , Shanghai, China (2011).
Zinner, T., Klein, D., Tutschku, K., Zseby, T., Tran-Gia, P., Shavitt, Y.: Performance of Concurrent Multipath Transmissions - Measurements and Model Validation.Proceedings of the 7th Conference on Next Generation Internet Networks (NGI). , Kaiserslautern, Germany (2011).
Concurrent multipath transport layer mechanisms have gained recently increasing interest in research and standardization because of the potential for bandwidth aggregation, load balancing and increased reliability. Multihomed end devices may benefit from IP-based multipath protocols like Multipath TCP or Concurrent Multipath Transmission via SCTP. In the future, concurrent multipath transport might be transparent to network and transport layer protocols as proposed by the concept of Transport Virtualization. This mechanism enables the pooling of heterogeneous transmission technologies or physical paths. However, the selection and application of multiple paths and its impact on the transmission is non-intuitive. Our prior work on transport virtualization discussed the impact of delay diversity of pooled paths on concurrent data transmissions. A mathematical model was introduced enabling the analysis of packet re-ordering that occurs due to different path delays. In this paper we extend our investigations by validating the previously presented analytical and simulative models with measurements performed in Planetlab Europe and the Etomic testbed.
Hirth, M., Hoßfeld, T., Tran-Gia, P.: Anatomy of a Crowdsourcing Platform - Using the Example of Microworkers.com.Workshop on Future Internet and Next Generation Networks (FINGNet). , Seoul, Korea (2011).
Since Jeff Howe introduced the term “crowdsourcing” in 2006 for the first time, crowdsourcing has be come a growing market in the current Internet. Thousands of workers categorize images, write articles or perform other small tasks on platforms like Amazon Mechanical Turk (MTurk), Microworkers or ShortTask. In this work, we want to give an inside view of the usage data from Microworkers and show that there are significant differences to the well studied MTurk. Further, we have a look at Microworkers from the perspective for a worker, an employer and the platform owner, in order to answer their most important questions: What jobs are most paid? How do I get my work done most quickly? When are the users of my platform active?
Pries, R., Jarschel, M., Schlosser, D., Klopf, M., Tran-Gia, P.: Power Consumption Analysis of Data Center Architectures.GreenNets. , Colmar, France (2011).
The high power consumption of data centers confronts the providers with major challenges. However, not only the servers and the cooling consume a huge amount of energy, but also the data center network architecture makes an important contribution. In this paper, we introduce different data center architectures and compare them regarding their power consumption. The results show that there are some differences which should not be neglected and that with only minor modifications of the architecture, it is possible to save a huge amount of energy.
Hoßfeld, T., Schatz, R., Seufert, M., Hirth, M., Zinner, T., Tran-Gia, P.: Quantification of YouTube QoE via Crowdsourcing.IEEE International Workshop on Multimedia Quality of Experience - Modeling, Evaluation, and Directions (MQoE). , Dana Point, CA, USA (2011).
This paper addresses the challenge of assessing and modeling Quality of Experience (QoE) for online video services that are based on TCP-streaming. We present a dedicated QoE model for YouTube that takes into account the key influence factors (such as stalling events caused by network bottlenecks) that shape quality perception of this service. As second contribution, we propose a generic subjective QoE assessment methodology for multimedia applications (like online video) that is based on crowdsourcing - a highly cost-efficient, fast and flexible way of conducting user experiments. We demonstrate how our approach successfully leverages the inherent strengths of crowdsourcing while addressing critical aspects such as the reliability of the experimental data obtained. Our results suggest that, crowdsourcing is a highly effective QoE assessment method not only for online video, but also for a wide range of other current and future Internet applications.
Zinner, T., Abboud, O., Hohlfeld, O., Hoßfeld, T., Tran-Gia, P.: Towards QoE Management for Scalable Video Streaming.21th ITC Specialist Seminar on Multimedia Applications - Traffic, Performance and QoE. , Miyazaki, Jap (2010).
Video streaming applications are a major driver for the evolution of the future Internet. In this paper we introduce a framework for QoE management for video streaming systems based on H.264/SVC codec, the scalable extension of H.264/AVC. A relevant feature is to control the user perceived quality of experience (QoE) by exploiting parameters offered by SVC. A proper design of a control mechanisms requires the quantification of the main influence parameters on the QoE. For this purpose, we conducted an extensive measurement study and quantified the influence of i) video resolution, ii) scaling method, iii) network conditions in terms of packet loss and iv) video content types on the QoE by means of the SSIM and PSNR full-reference metrics. Further, we discuss the trade-off between these different control knobs and their influence on the QoE.
Abboud, O., Zinner, T., Pussep, K., Oechsner, S., Steinmetz, R., Tran-Gia, P.: A QoE-Aware P2P Streaming System based on Scalable Video Coding.10th IEEE International Conference on Peer-to-Peer Computing 2010 - IEEE P2P 2010. , Delft, Netherlands (2010).
Wamser, F., Mittelstädt, D., Staehle, D., Tran-Gia, P.: Advanced Interference Mitigation with Frequency Reuse Schemes in the IEEE 802.16m Uplink.ACM MSWIM 2010. pp. 132-139. , Bodrum, Turkey (2010).
Fractional frequency reuse is one of the key interference mitigation schemes of the IEEE 802.16m draft standard. This paper proposes a resource allocation strategy for the uplink fractional frequency reuse in the variant soft frequency reuse. Soft frequency reuse means that the resources of every sector are separated into a home partition and two side partitions. While resources of the home partition may be allocated to all users, resources of the side partitions are available for cell center users only. The main contribution of this paper is to use the most robust and power-efficient modulation and coding schemes on the side partitions as long as resources are available. A simulation study shows that with non-saturated users the system capacity can be increased when preferring power-efficient modulation and coding schemes on the side partitions.
Zinner, T., Tutschku, K., Nakao, A., Tran-Gia, P.: Using Concurrent Multipath Transmission for Transport Virtualization: Analyzing Path Selection.Proceedings of the 22nd International Teletraffic Congress (ITC). , Amsterdam, Netherlands (2010).
The concept of Transport Virtualization (TV) enhances the capabilities of future networks. TV enables transport mechanisms with arbitrary resource usage independent of the underlying transport system. The simplest form of TV can be achieved by collecting multiple transport resources (even from different virtual networks or providers) and selecting the best resources for exclusive or concurrent use. However, the selection and application of concurrent paths is complex and its impact on the transmission is non-intuitive. Path length diversity of different concurrent paths inevitably introduces out-of-order packet delivery.We present and discuss a mathematical model for the analysis of the fundamental behavior and influence factors for packet re-ordering in concurrent multipath transmissions. Our model facilitates the understanding of path selection algorithms for multipath transport virtualization.
Tutschku, K., Zinner, T., Nakao, A., Tran-Gia, P.: Network Virtualization: Implementation Steps Towards the Future Internet.KiVS 2009. , Kassel (2009).
In this paper we will investigate why and how Network Virtualization (NV) can overcome the shortfalls of the current system and how it paves the way for the Future Internet. Therefore, we will first discuss some major deficiencies and achievements of today’s Internet. Afterwards, we identify three major building blocks of NV: a) the use of application-specific routing overlays, b) the safe consolidation of resources by OS virtualization on a generic infrastructure, and c) the exploitation of the network diversity for performance enhancements and for new business models, such as the provisioning of intermediate nodes or path oracles. Subsequently, we discuss an implementation scheme for network virtualization or routing overlays based on one-hop source routers (OSRs). The capabilities of the combination of NV and OSRs are demonstrated by a concurrent multipath transmission (CMP) mechanism (also known as stripping) for obtaining high throughput transmission pipes. The suggested stripping mechanism constitutes a first instance of a refinement of the concept of NV, the idea of transport system virtualization.
Pries, R., Staehle, D., Stoykova, M., Staehle, B., Tran-Gia, P.: Wireless Mesh Network Planning and Optimization through Genetic Algorithms.The Second International Conference on Advances in Mesh Networks, MESH 2009. p. 7. , Athens/Glyfada, Greece (2009).
Wireless Mesh Networks (WMNs) are a promising technology for providing broadband wireless access to the end user. They offer a higher degree of flexibility compared to traditional networks but on the expense of a more complex structure. Thus, planning and optimization of WMNs is a challenge. In this paper, we address this challenge using genetic algorithms. Genetic algorithms are able to evaluate and optimize large-scale WMNs in relatively small computation time. The results prove the effectiveness of the genetic operators to optimize the routing and channel assignment in WMNs.
Pries, R., Staehle, D., Oechsner, S., Menth, M., Menth, S., Tran-Gia, P.: On the Unfair Channel Access Phenomenon in Wireless LANs.21st International Teletraffic Congress (ITC 21). , Paris, France (2009).
This paper shows that the relative collision probability for packets in Wireless LAN 802.11 networks decreases with increasing load offered by the respective station. This denotes a clearly unfair channel access which is important to be aware of, e.g., when collision probabilities are measured and used for reactive control of contention windows. We model the unfair channel access phenomenon analytically and semi-analytically for bidirectional constant bit rate and unidirectional TCP traffic and compare the results with those from simulations.
Pries, R., Staehle, D., Stoykova, M., Staehle, B., Tran-Gia, P.: A Genetic Approach for Wireless Mesh Network Planning and Optimization.IWCMC 2009 Planning and Optimization of Wireless Communication Networks (PlanNet). , Leipzig, Germany (2009).
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.
Pries, R., Wamser, F., Staehle, D., Heck, K., Tran-Gia, P.: On Traffic Characteristics of a Broadband Wireless Internet Access.Next Generation Internet Networks 2009 (NGI 2009). , Aveiro, Portugal (2009).
Internet traffic measurements and traffic characterization are essential for managing and optimizing network infrastructures. The increasing number of wireless Internet users and the changing application demands require consecutive traffic measurements. Therefore, we have performed measurements of home users at a broadband wireless access service provider in order to reflect the current traffic characteristics. In this paper, we present the results of these measurements like application distributions as well as changing traffic characteristics caused by user demands and new services. The results are used by a network service provider to optimize its network performance in order to give Quality of Service (QoS) guarantees for home users in its fixed wireless network.
Pries, R., Wamser, F., Staehle, D., Heck, K., Tran-Gia, P.: Traffic Measurement and Analysis of a Broadband Wireless Internet Access.IEEE VTC Spring 09. , Barcelona, Spain (2009).
The increasing broadband wireless Internet usage and the limited wireless resources require a careful network management and optimization of the wireless Internet Service Providers (ISPs). Unfortunately, those providers often just have statistics about the overall usage and limited knowledge about the detailed application distribution as well as the traffic characteristics. In this paper we present user and traffic characteristics measured at a broadband wireless Internet access. The results show that the applications change quickly but the general characteristics like packet size and TCP/UDP percentage have not changed during the last years.
Pries, R., Staehle, D., Menth, S., Menth, M., Tran-Gia, P.: Impact of Best Effort Frame Bursting in IEEE 802.11 Networks.IEEE VTC Spring 09. , Barcelona, Spain (2009).
Wireless LAN strongly prioritizes high priority traffic over low priority best effort traffic. This causes reduced access to the medium for low priority traffic and under some conditions even leads to starvation. To compensate the throughput reduction of low priority traffic, we propose frame bursting in this paper. That means low priority traffic is sent infrequently, but many frames may be sent in a burst. Our simulation results show that the throughput of the low priority best effort traffic class can be significantly increased without disrupting high priority traffic.
Oechsner, S., Hoßfeld, T., Tran-Gia, P.: Performance Evaluation of a Distributed Lookup System for a Virtual Database Server.20th ITC Specialist Seminar. , Hoi An, Vietnam (2009).
Services offered today rely on large amounts of data that can be accessed fast and reliably. One technical solution providing both acceptable speed and high reliability are distributed databases, which can be accessed from an application as one virtual database server. The virtualization here hides complexity introduced by distributing the service to a set of machines. In this paper, we will present a DHT-based architecture implementing a lookup layer for such a database, which preserves important features such as self-organization from its DHT roots, but still offers a good performance for time-critical applications. Additionally, first anaytical results are given, which show some of the basic mechanisms at work in such systems.
Tutschku, K., Zinner, T., Nakao, A., Tran-Gia, P.: Re-sequencing Buffer Occupancy of a Concurrent Multipath Transmission Mechanism for Transport System Virtualization.KiVS 2009. , Kassel (2009).
From the viewpoint of a methodology, the concept of Net- work Virtualization (NV) extends beyond pure operational issues. In this paper, we will first transfer the concept of location independence of resources, as known in operating systems, to the area of data transport in communication networks. This idea is denoted as transport sys- tem virtualization (TSV). We will outline an example for TSV which uses concurrent multipath (CMP) transmission and discuss an important performance issue of CMP transmission, the re-sequencing buer occupancy probability distribution. The investigation of this probability distribution gives insights in how to select the set of paths when using CMP transmission for transport system virtualization.
Zinner, T., Tutschku, K., Nakao, A., Tran-Gia, P.: Performance Evaluation of Packet Re-ordering on Concurrent Multipath Transmissions for Transport Virtualization.20th ITC Specialist Seminar. , Hoi An, Viet nam (2009).
Hoßfeld, T., Hock, D., Tran-Gia, P., Tutschku, K., Fiedler, M.: Testing the IQX Hypothesis for Exponential Interdependency between QoS and QoE of Voice Codecs iLBC and G.711.18th ITC Specialist Seminar on Quality of Experience. , Karlskrona, Sweden (2008).
Pries, R., Staehle, D., Tran-Gia, P., Gutbrod, T.: A Seamless Vertical Handover Approach.Wireless and Mobility 2008, LNCS 5122. , Barcelona, Spain (2008).
Pries, R., Hock, D., Bayer, N., Siebert, M., Staehle, D., Rakocevic, V., Xu, B., Tran-Gia, P.: Dynamic Bandwidth Control in Wireless Mesh Networks: A Quality of Experience based Approach.18th ITC Specialist Seminar on Quality of Experience. , Karlskrona, Sweden (2008).
Wireless Mesh Networks (WMNs) are gaining an increasingly important role in next generation wireless networks. Due to their advantages over other wireless and wired networks, WMNs are undergoing rapid progress and are supposed to deliver wireless services for a large variety of applications. Especially real-time applications such as voice over IP make high demands on wireless mesh networks. 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 of the overall value of the provided service or application. In this paper, we present a dynamic bandwidth control mechanism which measures the current situation in the network and adapts the bandwidth in order to ensure a high QoE level. The mechanism is implemented in a Wireless LAN mesh testbed and the results show that real-time applications are successfully protected from disturbing best effort traffic flows.
