Iffländer, L., Geissler, S., Walter, J., Beierlieb, L., Kounev, S.: Addressing Shortcomings of Existing DDoS Protection Software Using Software-Defined Networking.9th Symposium on Software Performance 2018 (SSP'18). , Hildesheim, Germany (2018).
DDoS attacks are becoming increasingly frequent and violent. A typical type of attack is the TCP SYN flood, inhibiting a server from opening new TCP connections. Current countermeasures to this attack introduce inefficiencies by either reducing computing resources on the service host or creating new network bottlenecks. In this work, we present a novel approach to mitigate TCP SYN flood attacks using software-defined networking. We perform an initial evaluation of a proof-of-concept implementation that exhibits performance measures close to existing countermeasures while circumventing their inefficiencies.
Hoßfeld, T., Metzger, F., Heegaard, P.E.: Traffic Modeling for Aggregated Periodic IoT Data.Proceedings of the 21st Conference on Innovation in Clouds, Internet and Networks (ICIN). , Paris, France (2018).
Metter, C., Burger, V., Hu, Z., Pei, K., Wamser, F.: Evaluation of the Detection Capabilities of the ONOS SDN Controller.7th IEEE International Conference on Communications and Electronics (IEEE ICCE 2018). pp. 96 - 101. , Hue, Vietnam (2018).
The process of monitoring the network, especially for larger ones, is very complex and contains many pitfalls. For instance the balance between granularity of information and their performance impact on the network. With the help of SDN this challenge can become easier, as it offers new methods, mechanisms and opportunities. One of the current most important Open Source controllers is the ONOS SDN controller. According to its developers it is a production ready controller that offers high availability due to its logically centralized and physically distributed architecture. But, as our investigations show, it is unable to cope with hazardous network conditions such as sporadic or recurring packet loss. It either does not detect packet loss or only detects it after long time periods, failing all common network availability targets.
Wehner, N., Wassermann, S., Casas, P., Seufert, M., Wamser, F.: Beauty is in the Eye of the Smartphone Holder - A Data Driven Analysis of YouTube Mobile QoE.14th International Conference on Network and Service Management (CNSM). , Rome, Italy (2018).
Measuring the Quality of Experience (QoE) undergone by cellular network users has become paramount for cellular ISPs. Given its overwhelming dominance and ever-growing popularity, this paper focuses on the analysis of QoE for YouTube in mobile networks. Using a large-scale dataset of crowdsourced YouTube QoE measurements collected in smartphones with YoMoApp, we analyze the evolution of multiple relevant QoE-related metrics over time for YouTube mobile users. The dataset includes measurements from more than 360 users worldwide, spanning over the last five years. Our data-driven analysis shows a systematic performance and QoE improvement of YouTube in mobile devices over time, accompanied by an improvement of cellular network performance and by an optimization of the YouTube streaming behavior for smartphones.
Seufert, M., Schwind, A., Waigand, M., Hoßfeld, T.: Potential Traffic Savings by Leveraging Proximity of Communication Groups in Mobile Messaging.14th International Conference on Network and Service Management (CNSM). , Rome, Italy (2018).
Communication groups in mobile messaging applications (MMAs) multiply the data transmissions, because every message has to be delivered to all members of the communication group. Thereby, they put a high load on mobile networks. As the number of recipients is still comparably small, the dataintensive user-generated content cannot be handled efficiently in large content delivery networks. However, small communication groups, such as groups of friends or teams, might often be in close proximity, which can be leveraged to locally deliver messages by applying edge caching or device-to-device (D2D) communication. In this work, a simulation study is conducted to investigate these potential traffic savings in the mobile network. It is based on a realistic communication model of the MMA WhatsApp and utilizes different models for human mobility. The user mobility and MMA communication are simulated for a single day in a small city to obtain the ratio of messages, which could be potentially transmitted locally when utilizing edge caching and D2D communication.
Moldovan, C., Skorin-Kapov, L., Heegaard, P.E., Hoßfeld, T.: Optimal Fairness and Quality in Video Streaming With Multiple Users.30th International Teletraffic Congress (ITC 30). p. 6. , Vienna, Austria (2018).
With the majority of video distribution services relying on the HTTP adaptive streaming paradigm, a great deal of research is geared towards developing algorithms and solutions for improving user perceived quality while making efficient use of available resources. Our goal is to provide the means for benchmarking such solutions in the context of multiple users accessing Video on Demand content while sharing a bottleneck link. For that purpose, we propose a quadratic problem formulation to compute the theoretical optimum in terms of adaptation strategies and corresponding segment downloads across multiple users under given bandwidth constraints. By aiming to maximize both service quality and fairness, we quantify and compare the impact of different fairness objectives (bandwidth fairness, pattern fairness, and session fairness) on resulting quality and achieved QoE fairness. Based on conducted simulations and parameter studies, our results demonstrate the benefits of optimizing for session fairness as compared to other approaches.
Seufert, M., Wehner, N., Casas, P., Wamser, F.: A Fair Share for All: Novel Adaptation Logic for QoE Fairness of HTTP Adaptive Video Streaming.(Best Paper Award) 14th International Conference on Network and Service Management (CNSM). , Rome, Italy (2018).
This paper presents a novel adaptation logic for HTTP adaptive streaming (HAS), which achieves not only a high Quality of Experience (QoE) but also high QoE fairness among independent and heterogeneous clients. The algorithm forces video clients to adapt the requested quality level based on the current network conditions and their individual bit rate requirements, such that the overall quality levels selected by all currently active streaming clients are fairly distributed, i.e., they do not diverge too much. The design of the algorithm is inspired by the well-known Transmission Control Protocol (TCP) congestion control, and drives heterogeneous clients to independently converge on similar quality levels without the need for communicating with each other and/or with a centralized controller in the network. By defining quality levels with equal visual quality, and preparing video representations accordingly, the quality level fairness is extended to QoE fairness. In this work, the design of the algorithm is described and a simulative performance evaluation is conducted to compare the QoE and QoE fairness of the proposed algorithm with other HAS adaptation logics.
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).
Metter, C., Burger, V., Hu, Z., Pei, K., Wamser, F.: Towards an Active Probing Extension for the ONOS SDN Controller.2018 28th International Telecommunication Networks and Applications Conference (ITNAC) (ITNAC 2018). p. 8. , Sydney, Australia (2018).
Network monitoring is a complex task and is always a trade-off between granularity of information and the performance impact of the monitoring itself on the network. SDN controllers, such as the ONOS SDN controller make this challenge easier as they can supply centralized information over the whole network. In our previous work we mathematically analyzed the built-in detection mechanism of ONOS and revealed a lack of detection performance and the vulnerability of this process to jitter. These results were also verified by measurements. In this paper we present an Active Probing extension for the ONOS SDN controller that overcomes these shortcomings by emitting probing packets that are transmitted through the network. Statistics over a history of those packets allow for the detection of packet loss. The evaluation by the means of measurements proves the benefits in terms of detection performance and controller load of this application. Furthermore, our extension is able to detect jitter being present in the network and to automatically adapt the probing process to these conditions.
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.
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).
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.
Lagerspetz, E., Flores, H., Mäkitalo, N., Hui, P., Nurmi, P., Tarkoma, S., Passarella, A., Ott, J., Reichl, P., Conti, M., Fiedler, M., Singh, J., Strufe, T., Hoßfeld, T.: Pervasive Communities in the Internet of People.Proceedings of the 1st International Workshop on Context-Awareness for Multi-Device Pervasive and Mobile Computing (PerCrowd). , Athens, Greece (2018).
Surminski, S., Moldovan, C., Hoßfeld, T.: Practical QoE Evaluation of Adaptive Video Streaming.Proceedings of the 19th International Conference on Measurement, Modelling and Evaluation of Computing Systems (MMB). , Erlangen, Germany (2018).
Borchert, K., Lange, S., Zinner, T., Hirth, M.: Identification of Delay Thresholds Representing the Perceived Quality of Enterprise Applications.The 2nd International Workshop on Quality of Experience Management. , Sardinia, Italy (2018).
Hoßfeld, T., Varela, M., Heegaard, P.E., Skorin-Kapov, L.: QoE Analysis of the Setup of Different Internet Services for FIFO Server Systems.Proceedings of the 19th International Conference on Measurement, Modelling and Evaluation of Computing Systems (MMB). , Erlangen, Germany (2018).
Hoßfeld, T., Metzger, F., Rossi, D.: Speed Index: Relating the Industrial Standard for User Perceived Web Performance to Web QoE.Proceedings of the 10th International Conference on Quality of Multimedia Experience (QoMEX 2018). , Sardinia, Italy (2018).
Volodina, E., Aziz, A., Rathgeb, E., Hoßfeld, T.: Application of Visual Analysis to Detect and Analyze Patterns in VoIP Attack Traffic.17th IEEE International Conference On Trust, Security And Privacy In Computing And Communications/12th IEEE International Conference On Big Data Science And Engineering (TrustCom/BigDataSE) (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.
Schwarzmann, S., Zinner, T., Sieber, C., Geissler, S.: Evaluation of the Benefits of Variable Segment Durations for Adaptive Streaming.The 2nd International Workshop on Quality of Experience Management. , Sardinia, Italy (2018).
HTTP Adaptive Streaming (HAS) is the de-facto standard for video delivery over the Internet. It enables the dynamic adaptation of video quality by splitting the video clip into small segments and providing multiple quality levels per segment. Current HAS streaming services typically utilize segments of equal durations. However, this leads to video encoding overhead as segments have to start with I-frames, independently of the encoded video content. In this paper we evaluate the prospects of variable segment durations, where video segments are aligned to the video characteristics. We evaluate the reduction of the encoding overhead and investigate its impact on the stalling probability using a theoretical model. It turns out that the variable approach outperforms the fixed approach in 86% of the evaluated cases with respect to video stalls.
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.
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.
Casas, P., Seufert, M., Wehner, N., Schwind, A., Wamser, F.: Enhancing Machine Learning based QoE Prediction by Ensemble Models.IEEE ICDCS 3rd Workshop on QoE-based Analysis and Management of Data Communication Networks. , Vienna, Austria (2018).
The number of smartphones connected to wireless networks and the volume of wireless network traffic generated by such devices have dramatically increased in the last few years, making it more challenging to tackle wireless network monitoring applications. The high-dimensionality of network data provided by current smartphone devices opens the door to the massive application of machine learning approaches to improve different wireless networking applications. In this paper we study the specific problem of Quality of Experience (QoE) prediction for popular smartphone apps, using machine learning models and in-smartphone measurements. We evaluate and compare different models for the analysis of smartphone generated data, including single models as well as machine learning ensembles such as bagging, boosting and stacking. Results suggest that, while decision-tree based models are the most accurate single models to predict QoE, ensemble learning models, and in particular stacking ones, are capable to significantly increase accuracy prediction and overall classification performance.
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.
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.
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.
Gray, N., Lange, S., Zinner, T., Pfaff, B., Hock, D.: Evaluation of a Distributed Control Plane for Managing Heterogeneous SDN-enabled and Legacy Networks.7th International Conference on Communications and Electronics (ICCE). , Hue, Vietnam (2018).
With the increasing number of devices, protocols and applications, today’s networks are becoming more and more complex. Hence, Software-defined Networking (SDN) tries to ad- dress this issue by separating the data from the control plane and by providing centralized interfaces for network configuration. As legacy devices cannot be replaced instantly due to high costs, both network segments have to be operated in coexistence with defined joints at their edges. To ensure a smooth operation, both controlling instances of these segments are required to exchange information. In this work, we design and implement a data model for storing the information needed to keep the controller and a Network Management System (NMS) synchronized, which are responsible for configuring the SDN-enabled network and the legacy devices respectively. For this, we implement and evaluate a total of three different synchronization strategies by the example of an SDN-based Bring Your Own Device (BYOD) use case. Index Terms—SDN, NMS, Management, Integration, Hetero- geneous Networks, Distributed Control Plane.
Metzger, F., Heger, R.: Exploring the Transmission Behaviour of Overwatch: The Source of Lag.30th International Teletraffic Congress (ITC 30) (2018).
This paper explores the full chain of lag contribution factors in a specific online multiplayer game, namely Overwatch: From creating input events over the network and back to displaying the results on the local screen. Together result in the dreaded end-to-end lag. which has a direct impact on the subjective quality one experiences when playing video games. In its investigation, this paper reveals surprising effects in the game's networking behavior that are omitted when colloquially talking about, e.g. a 60 Hz update rate, but must be considered nonetheless. These insights, gained from examining network traces of Overwatch matches that were played on a realistic, resource constrained PC, can then be used to refine end-to-end lag simulation models and reach a better understanding of all responsible components.
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.
Moldovan, C., Burger, V., Metzger, F., Surminski, S., Hoßfeld, T.: Viability of Wi-Fi Caches in an Era of HTTPS Prevalence.IEEE ICC'17: Bridging People, Communities, and Cultures. , Paris, France (2017).
Caches are often employed to better manage the ever-growing amount of global Internet traffic. Particularly, reverse proxies are often used to free up congested peering links and reduce inter-domain traffic. In addition, caches place content close to the edge, leading to lower latency which can be beneficial for many applications. In an effort to bring content even closer to end devices, home routers and public access points are now in the spotlight as a novel location for caches. Compared to CDNs, a Wi-Fi router only offers scarce storage and processing capabilities, putting an increased emphasis on resource management. In addition, a large share of traffic is transmitted through secured connections preventing the use of forward caches and other middle boxes. This paper strives to analyze how effective caching can be in public Wi-Fi routers. For this purpose, we conducted a field study with caches at public Wi-Fi hotspots in a field study. In addition, we present a queueing model for caches that we use to perform a mean-value analysis. We compare results from both methods in a performance analysis. Our results provide insights into difficulties of caching systems that are caused by an increase in the ratio of secured connections in the Internet.
Lareida, A., Hoßfeld, T., Stiller, B.: The BitTorrent Peer Collector Problem.IFIP/IEEE International Symposium on Integrated Network Management. , Lisbon, Portugal (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.
Surminski, S., Moldovan, C., Hoßfeld, T.: Saving Bandwidth by Limiting the Buffer Size in HTTP Adaptive Streaming.MMBnet 2017 Proceedings of the 9th GI/ITG Workshop. , Hamburg, Germany (2017).
Video streaming is one of the most bandwidth-intensive applications on the Internet. In HTTP adaptive video streaming the video quality is selected according to the available bandwidth. To compensate bandwidth fluctuations, players use a buffer in order to ensure a smooth video output. On one hand, if the buffer runs empty, the video playback stops, which users experience as negative. On the other hand, if the user aborts video playback, the video in the buffer was unnecessarily transmitted, hence this bandwidth was wasted. In this paper, we present a study in which we investigate the behavior of two video players and different buffer configurations in real-world bandwidth scenarios. Thereby, we focus on the dimensioning of the buffer size and the tradeoff between wasted bandwidth and the playback quality
Hoßfeld, T., Fiedler, M., Gustafsson, J.: Betas: Deriving Quantiles from MOS-QoS Relations of IQX Models for QoE Management.IFIP/IEEE International Workshop on Quality of Experience Management (QoE-Management). , Lisbon, Portugal (2017).
Moldovan, C., Hagn, K., Sieber, C., Kellerer, W., Hoßfeld, T.: Keep Calm and Don’t Switch: About the Relationship Between Switches and Quality in HAS.29th International Teletraffic Congress (ITC 29). p. 6. , Genoa, Italy (2017).
Video streaming has established itself as the main method to consume multimedia content on the Internet. The most widespread technique is HTTP Adaptive Streaming which is used by large video service platforms such as YouTube and Netflix. In order to guarantee a high QoE, different adaptation strategies have been developed that lead to different video playout patterns. While some strategies may be more aggressive than others and often adapt the video quality, it is not clear which strategy is the best. In this paper, we want to identify the trade-off between the av- erage video quality and switches in the quality during playout. We do this with a user-centric view and try to optimize the adaptation depending on the user preference with a quadratic program. This work allows us to put existing and future video adaptation algorithms in perspective with respect to user preferences. Our results show that the video quality can already be increased greatly by allowing few switches while more switches lead to diminishing gains. This is a novel discovery that is important for user-centric QoE-management which is of high interest for ISPs and video service providers.
Borchert, K., Hirth, M., Zinner, T., Göritz, A.: Collecting Subjective Ratings in Enterprise Environments.9th International Conference on Quality of Multimedia Experience (QoMEX). , Erfurt, Germany (2017).
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.
Geissler, S., Gebert, S., Herrnleben, S., Zinner, T., Bauer, R., Jarschel, M.: TableVisor 2.0: Towards Full-Featured, Scalable and Hardware-Independent Multi Table Processing.NetSoft 2017, Best Student Paper Award (2017).
Modern Software Defined Networking (SDN) appli- cations rely on sophisticated packet processing. However, there is a mismatch between control plane requirements and data plane capabilities caused by increasing hardware heterogeneity. To overcome this challenge, we propose TableVisor, a proxy-layer for the OpenFlow control channel that enables the flexible and scalable abstraction of multiple physical devices into one emu- lated data plane switch that meets the requirements of the control plane application. TableVisor registers with the SDN controller as a single switch with use-case specific capabilities. It translates the instructions and rules from the control application towards the appropriate physical device where they are executed. In this paper, we present the updated architecture and functionality of TableVisor as well as first evaluation results based on testbed experiments.
Zinner, T., Geissler, S., Helmschrott, F., Spinsante, S., Braeken, A.: An AAL-Oriented Measurement-based Evaluation of Different HTTP-based Data Transport Protocols.International Workshop on Protocols, Applications and Platforms for Enhanced Living Environments (2017).
A key requirement for Active and Assisted Living (AAL) environments is the exchange of data between different communication endpoints to support wide range of services and applications. Used communication protocols need to support the bidirectional flow of information and have to be optimized with regard to security or latency constraints. To address these issues, RESTful approaches have recently gained much attention from the community. In this context, different application layer transport protocols can be used to realize the required data exchange. Besides HTTP/1.1, developed and standardized in the 1990s, new protocols like HTTP/2 and the QUIC transfer protocol my be suitable candidates. The impact of the different protocols on the overall performance for web and AAL services is still an open research question. This paper narrows this gap by conducting a measurement-based comparison of the three described protocols with regard to their performance in terms of web page loading times for Google web services.
Zinner, T., Geissler, S., Helmschrott, F., Burger, V.: Comparison of the Initial Delay for Video Playout Start for Different HTTP-based Transport Protocols.Workshop on Quality of Experience Management (2017).
This paper details a measurement study on the impact of different HTTP-based application layer protocols, namely HTTP/1, HTTP/2 and QUIC, on video streaming performance. In this context we evaluate the influence on the initial delay until video playout is started using the live version of the YouTube platform. Furthermore, we evaluate how different network parameters, i.e. bandwidth, RTTs and packet loss influence the different protocols. This work presents an verview over the characteristics of the compared protocols and presents a detailed measurement methodology on how the data has been obtained. Finally, the observed data is evaluated in the context of YouTube video streaming.
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.
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.
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.
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.
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.
Borchert, K., Hirth, M., Zinner, T., Göritz, A.: Designing a Survey Tool for Monitoring Enterprise QoE.ACM SIGCOMM Workshop on QoE-based Analysis and Management of Data Communication Networks (Internet-QoE). , Los Angeles, CA, USA (2017).
Enterprise applications like SAP are part of the day-to-day work of a large number of employees. Similar to many modern applications, enterprise applications are often implemented in a distributed fashion and consequently suffer from network degradations resulting in impairments like increased loading delays. While the influence of these impairments on the perceived quality of users is well researched for consumer applications and network services, the impact of these impairments in a business environment is still unclear. To address this gap we develop a non-intrusive software tool for continuously collecting subjective ratings on the performance of an enterprise application from a large crowd of employees. Based on the feedback from a company and results from two initial field studies we discuss the specific challenges when assessing the perceived quality of employees during regular working hours and point our further research directions.
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.
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).
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
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).
Seufert, M., Lange, S., Meixner, M.: Automated Decision Making based on Pareto Frontiers in the Context of Service Placement in Networks.29th International Teletraffic Congress (ITC). , Genoa, Italy (2017).
Virtualization paradigms like cloud computing, software defined networking (SDN), and network functions virtualization (NFV) provide advantages with respect to aspects like flexibility, costs, and scalability. However, management and orchestration of the resulting networks also introduce new challenges. The placement of services, such as virtual machines~(VMs), virtualized network functions~(VNFs), or SDN controllers, is a multi-objective optimization task that confronts operators with a multitude of possible solutions that are incomparable among each other. The goal of this work is to investigate mechanisms that enable automated decision making between such multi-dimensional solutions. To this end, we investigate techniques from the domain of multi-attribute decision making that aggregate the performance of placements to a single numeric score. A comparison between resulting rankings of placements shows that many techniques produce similar results. Hence, placements that achieve good rankings according to many approaches might be viable candidates in the context of automated decision making. In order to illustrate the functionality of the different scoring mechanisms, we perform a case study on a single network graph and a fixed number of objectives and service instances. Additionally, we present aggregated results from broad evaluations on the Internet Topology Zoo and a larger number of objectives as well as varying numbers of service instances. These allow making more reliable statements about the mechanisms' performance and agreement.
Borchert, K., Hirth, M., Schnitzer, S., Rensing, C.: Impact of Task Recommendation Systems in Crowdsourcing Platforms.Workshop on Responsible Recommendation at RecSys 2017. , Como, Italy (2017).
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., Moldovan, C., Burger, V., Hoßfeld, T.: Applicability and Limitations of a Simple WiFi Hotspot Model for Cities.13th International Conference on Network and Service Management (CNSM). , Tokio, Japan (2017).
Offloading mobile Internet data via WiFi has emerged as an omnipresent trend. WiFi networks are already widely deployed by many private and public institutions (e.g., libraries, cafes, restaurants) but also by commercial services to provide alternative Internet access for their customers and to mitigate the load on mobile networks. Moreover, smart cities start to install WiFi infrastructure for current and future civic services, e.g., based on sensor networks or the Internet of Things. A simple model for the distribution of WiFi hotspots in an urban environment is presented. The hotspot locations are modeled with a uniform distribution of the angle and an exponential distribution of the distance, which is truncated to the city limits. We compare the characteristics of this model in detail to the real distributions. Moreover, we show the applicability and the limitations of this model, and the results suggest that the model can be used in scenarios, which do not require an accurate spatial collocation of the hotspots, such as offloading potential, coverage, or signal strength.
Hoßfeld, T., Heegaard, P.E., Skorin-Kapov, L., Varela, M.: No Silver Bullet: QoE Metrics, QoE Fairness, and User Diversity in the Context of QoE Management.9th International Conference on Quality of Multimedia Experience (QoMEX 2017). , Erfurt, Germany (2017).
Hirth, M., Allendorf, F., Metzger, F., Schwartz, C.: Assessing the Accuracy of Network Estimations in the DOTA 2 Game Client.Workshop on Perceptual Quality of Systems (PQS). , Berlin, Germany (2016).
Online video games and the subjective quality of player inter- actions with them rely on good network conditions. Almost equally important is a good and timely knowledge of such conditions in order to take proper countermeasures to worsening conditions. To this end, many online video games include components for estimating the current network status. In this paper, we examine the accuracy of those estimations for the popular competitive multiplayer game DOTA 2. Our results show that the game client is capable of performing a good estimation of the delay and packet loss, but only after a rather large initial delay.
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.
Hoßfeld, T., Skorin-Kapov, L., Heegaard, P.E., Varela, M., Chen, K.-T.: On Additive and Multiplicative QoS-QoE Models for Multiple QoS Parameters.5th ISCA/DEGA Workshop on Perceptual Quality of Systems (PQS) (2016).
Sieber, C., Heegaard, P.E., Hoßfeld, T., Kellerer, W.: Sacrificing efficiency for quality of experience: YouTube's redundant traffic behavior.IFIP Networking Conference (2016).
Liotou, E., Hoßfeld, T., Moldovan, C., Metzger, F., Tsolkas, D., Passas, N.: Enriching HTTP adaptive streaming with context awareness: A tunnel case study.IEEE International Conference on Communications Workshops (ICC) (2016).
Moldovan, C., Sieber, C., Heegaard, P.E., Kellerer, W., Hoßfeld, T.: YouTube Can Do Better: Getting the Most Out of Video Adaptation.ITC and IEEE Workshop on QoE Centric Management (QCMan) (2016).
Metzger, F., Rafetseder, A., Schwartz, C., Hoßfeld, T.: Games and frames: A strange tale of QoE studies.Eighth International Conference on Quality of Multimedia Experience (QoMEX) (2016).
Moldovan, C., Metzger, F.: Bridging the Gap between QoE and User Engagement in HTTP Video Streaming.28th International Teletraffic Congress (ITC 28) (2016).
On video streaming platforms, users expect a high Quality of Experience (QoE). In contrast, service and content providers aim at high User Engagement, most notably because their revenue is usually dependent on it. In order to satisfy users, it is critical to know how QoE is related to the User Engagement. However, no model for this relation exists yet. Current approaches to managing QoE are usually based on traffic analysis. However, this will become more difficult in the future since the encryption of Internet traffic progresses. In this paper, we present an approach to bringing QoE and User Engagement together with video streaming as the use case. We do this by fitting existing measurement data of User Engagement to obtain a model. Furthermore, we extend the existing queuing model for QoE and investigate the correlation between QoE and User Engagement in a simulation. Hereby, we model different scenarios where we quantify network bandwidth and video requirements. Our results show that there is a strong correlation between QoE and User Engagement. Additionally, we observe that simple buffer policies, which do not rely on buffer information, can still perform well. These revelations open the way for new approaches to QoE Management in the future Internet.
Moldovan, C., Hoßfeld, T.: Impact of Variances on the QoE in Video Streaming.ITC and IEEE Workshop on QoE Centric Management (QCMan) (2016).
Sackl, A., Schatz, R., Hoßfeld, T., Metzger, F., Lister, D., Irmer, R.: QoE Management made uneasy: The case of Cloud Gaming.IEEE Workshop on Quality of Experience-based Management for Future Internet Applications and Services (QoE-FI) (2016).
Schwarzmann, S., Zinner, T., Dobrijević, O.: Towards a Framework for Comparing QoE-Centric Mechanisms of Application-Network Interaction.Proceedings of the 4th International IEEE Workshop on Quality of Experience Centric Management (2016). , Würzburg (2016).
Burger, V., Zinner, T.: Performance Analysis of Hierarchical Caching Systems with Bandwidth Constraints.Proceedings of the International Telecommunication Networks and Applications Conference. , Dunedin, New Zealand (2016).
The vast majority of Internet traffic is carried by content delivery networks. A high potential to bring content even closer to consumers and to reduce energy cost is achieved by the nano data center (NaDa) concept that has been proposed in recent work. In this approach the capacity available on small devices such as home gateways is used to support content delivery in an hierarchical caching system. In this work, we present a method to determine the efficiency of hierarchical content delivery networks with limited bandwidth, such as in the NaDa approach, analytically. We analyze the Internet Census Dataset to assess the number of available devices on autonomous system level. We evaluate the potential of hierarchical cache networks with bandwidth constraints to assist content delivery and determine its limits.
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.
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.
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.
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.
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.
Zinner, T., Hirth, M., Fischer, V., Hohlfeld, O.: ERWIN - Enabling the Reproducible Investigation of WaItiNg Times for Arbitrary Workflows.8th International Conference on Quality of Multimedia Experiene (QoMEX). , Lisbon, Portugal (2016).
Delay effects can impact the Quality of Experience of interactive systems, which motivates research assessing delay impairments, mostly for web based systems. Current studies follow individual methodologies and typically assesses individual and custom-made web pages, whose construction requires expert knowledge in web technologies. A range of native, non-web applications cannot be easily modified for delay studies. Thus, a generalized methodology for assessing delay impacts for a broad range of applications that is assessable to researchers without (web) development expertise is still missing. This paper con- tributes to this open problem by i) presenting a new methodology for reproducible delay assessments in a broad class of (web-based) systems and ii) presenting an open-source implementation to be used by the community. This methodology particularly aims at making delay assessment available to a broad range of researchers by avoiding programming skills and thus by lowering the barrier for setting-up delay assessments.
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.
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.
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.
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.
Borchert, K., Hirth, M., Zinner, T., Mocanu, D.C.: Correlating QoE and Technical Parameters of an SAP System in an Enterprise Environment.QCMan IEEE Workshop on QoE centric Management (2016).
Seufert, M., Lange, S., Meixner, M.: Automated Decision Making Methods for the Multi-objective Optimization Task of Cloud Service Placement.1st International Workshop on Programmability for Cloud Networks and Applications (PROCON). , Würzburg, Germany (2016).
The network functions virtualization (NFV) paradigm provides advantages with respect to aspects like flexibility, costs, and scalability of networks. However, management and orchestration of the resulting networks also introduce new challenges. The placement of services and virtualized network functions (VNFs) is a multi-objective optimization task that confronts operators with a multitude of possible solutions that are incomparable among each other. The goal of this work is to investigate mechanisms that enable automated decision making between such multi dimensional solutions. To this end, we investigate techniques from the domain of multi attribute decision making that aggregate the performance of placements to a single numeric score. A comparison between resulting rankings of placements shows that many techniques produce similar results. Hence, placements that achieve good rankings according to many approaches might be viable candidates in the context of automated decision making.
Seufert, M., Hoßfeld, T.: One Shot Crowdtesting: Approaching the Extremes of Crowdsourced Subjective Quality Testing.5th ISCA/DEGA Workshop on Perceptual Quality of Systems (PQS). , Berlin, Germany (2016).
Crowdsourcing studies for subjective quality testing have become a particularly useful tool for Quality of Experience researchers. Typically, crowdsouring studies are conducted by many unsupervised workers, which rate the perceived quality of several test conditions during one session (mixed within-subject test design). However, those studies often show to be very sensitive, for example, to test instructions, design, and filtering of unreliable participants. Moreover, the exposure of several test conditions to single workers potentially leads to an implicit training and anchoring of ratings. Therefore, this works investigates the extreme case of presenting only a single test condition to each worker (completely between-subjects test design). The results are compared to a typical crowdsourcing study design with multiple test conditions to discuss training effects in crowdsourcing studies. Thus, this work investigates if it is possible to use a simple ``one shot'' design with only one rating of a large number of workers instead of sophisticated (mixed or within-subject) test designs in crowdsourcing.
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.
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).
Seufert, M., Burger, V., Kaup, F.: Evaluating the Impact of WiFi Offloading on Mobile Users of HTTP Adaptive Video Streaming.5th IEEE International Workshop on Quality of Experience for Multimedia Communications (QoEMC). , Washington, DC, USA (2016).
In a recent trend to lessen the load on cellular networks in cities, users are offered to offload mobile connections to lower cost WiFi networks. In this work, we conduct a simulative performance evaluation of the impact of WiFi offloading for a mobile end user of a HTTP adaptive video streaming (HAS) service depending on availability and range of the WiFi hotspots. The simulation is based on connectivity measurements from a German city and evaluates the key performance indicators for the QoE of HAS, i.e., initial delay, stalling, and quality adaptation. Additionally, a smartphone energy model is applied to assess the energy consumption during the streaming. The results indicate that WiFi offloading of HAS connections to public WiFi hotspots is not attractive for end users both in terms of QoE and energy consumption. However, it can be shown that WiFi offloading can be beneficial also for end users in case high bandwidths can be received via WiFi.
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.
Metzger, F., Rafetseder, A., Schwartz, C.: A Comprehensive End-to-End Lag Model for Online and Cloud Video Gaming.Proc. 5th ISCA/DEGA Workshop on Perceptual Quality of Systems (PQS 2016) (2016).
To further the knowledge of basic game mechanics and improve future video game Quality of Experience (QoE) studies we present a model and simulation for End-to-End (E2E) lag in networked and cloud computer games. E2E lag describes the latency between a user's action and the display of the action's results on the screen, thus providing both a basic measure for interactivity and a fundamental parameter to derived QoE metrics. In contrast to E2E lag models that focus on the network Round-Trip Time (RTT), the presented work also factors in the game's tickrate and framerate (and codec latencies in the case of cloud games). This reveals side effects that can entirely mask the network delay's contribution to the total lag, an important notion to consider for future game studies.
Dinh-Xuan, L., Schwartz, C., Hirth, M., Wamser, F., Truong Thu, H.: Analyzing the Impact of Delay and Packet Loss on Google Docs.7th International Conference on Mobile Networks and Management. , Santander, Spain (2015).
Software as a Service allows end users to use complex soft- ware directly from their browsers, transferring heavy computation to servers in the cloud. One use of this paradigm is word processing, former a classic use cases of Thin-Client computing. Similar to Thin-Client systems, the network parameters are an important influence factor for the cloud application performance. In this paper, we study Google Docs as an example for online word processing tools. We consider a traditional single user scenario as well as a collaborative scenario with two users working on one document simultaneously. We identify multiple relevant sub-processes per scenario as performance metrics and use a testbed to automatically evaluate the performance of Google Docs under varying network parameters. The main contributions of the paper are (1) the quantification of the impact of network parameters such as delay and packet loss on application performance metrics for both scenarios and (2) linear regression models to derive the application performance for giving network parameters.
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.
Seufert, M., Hoßfeld, T., Sieber, C.: Impact of Intermediate Layer on Quality of Experience of HTTP Adaptive Streaming.11th International Conference on Network and Service Management (CNSM). , Barcelona, Spain (2015).
HTTP Adaptive Streaming (HAS) adapts the video quality to the current network condition by switching between different quality layers. As HAS was shown to perform better than classical video streaming, it is becoming increasingly popular. Recent research showed that quality switch amplitude and time on layer have an impact on the Quality of Experience (QoE) of HAS. However, those studies focused only on adaptation between two layers so far. This work extends these findings by taking adaptation between three layers into account. Thereby, especially the impact of an intermediate layer on user perceived quality is investigated. Crowdsourcing experiments were conducted in order to collect subjective ratings for adaptation between three layers. The results indicate that the quality of each layer and the time on each layer are important QoE parameters. This encourages the usage of temporal pooling approaches for QoE prediction and QoE-aware traffic management. Therefore, mean pooling of per-frame metrics will be applied and its performance will be validated with the subjective crowdsourcing results.
Casas, P., Gardlo, B., Seufert, M., Wamser, F., Schatz, R.: Taming QoE in Cellular Networks: from Subjective Lab Studies to Measurements in the Field.11th International Conference on Network and Service Management (CNSM). , Barcelona, Spain (2015).
A quarter of the world population will be using smartphones to access the Internet in the near future. In this context, understanding the Quality of Experience (QoE) of popular apps in such devices becomes paramount to cellular network operators, who need to offer high quality levels to reduce the risks of customers churning for quality dissatisfaction. In this paper we address the problem of QoE provisioning in smartphones from a double perspective, combining the results obtained from subjective lab tests with end-device passive measurements and QoE crowd-sourced feedback obtained in operational cellular networks. The study addresses the impact of the downlink bandwidth on the QoE of three popular smartphone apps: YouTube, Facebook and Google Maps. As a main contribution, we show that the results obtained in the lab are highly applicable in the live scenario, as mappings track the QoE provided by users in real networks. We additionally provide hints and bandwidth thresholds for good QoE levels on such apps, as well as discussion on end-device passive measurements and analysis. The results presented in this paper provide a sound basis to better understand the QoE requirements of popular mobile apps, as well as for monitoring the underlying provisioning network. To the best of our knowledge, this is the first paper providing such a comprehensive analysis of QoE in mobile devices, combining network measurements with users QoE feedback in lab tests and operational networks.
Hoßfeld, T., Skorin-Kapov, L., Haddad, Y., Pocta, P., Siris, V., Zgank, A., Melvin, H.: Can context monitoring improve QoE? A case study of video flash crowds in the Internet of Services.Third IFIP/IEEE International Workshop on Quality of Experience Centric Management. , Ottawa, Canada (2015).
Varela, M., Skorin-Kapov, L., Mäki, T., Hoßfeld, T.: QoE in the Web: A Dance of Design and Performance.7th International Workshop on Quality of Multimedia Experience (QoMEX). , Costa Navarino, Greece (2015).
Hoßfeld, T., Heegaard, P.E., Varela, M.: QoE beyond the MOS: Added Value Using Quantiles and Distributions.7th International Workshop on Quality of Multimedia Experience (QoMEX). , Costa Navarino, Greece (2015).
Hoßfeld, T., Redi, J.: Journey through the crowd: Best Practices and Recommendations for Crowdsourced QoE.7th International Workshop on Quality of Multimedia Experience (QoMEX). , Costa Navarino, Greece (2015).
Reichl, P., Egger, S., Möller, S., Kilkki, K., Fiedler, M., Hoßfeld, T., Tsiaras, C., Asrese, A.: The Unexpected QoE Killer: When the Network Emulator Misshapes Traffic and QoE.7th International Workshop on Quality of Multimedia Experience (QoMEX) (2015).
Metzger, F., Steindl, C., Hoßfeld, T.: A Simulation Framework for Evaluating the QoS and QoE of TCP-based Streaming in an LTE Network.27th International Teletraffic Congress (ITC). , Ghent, Belgium (2015).
Gardlo, B., Egger, S., Hoßfeld, T.: Do Scale-Design and Training Matter for Video QoE Assessments through Crowdsourcing?Fourth International Workshop on Crowdsourcing for Multimedia (CrowdMM) (2015).
Redi, J., Siahaan, E., Korshunov, P., Habigt, J., Hoßfeld, T.: When the Crowd Challenges the Lab: Lessons Learnt from Subjective Studies on Image Aesthetic Appeal.Fourth International Workshop on Crowdsourcing for Multimedia (CrowdMM) (2015).
Burger, V., Darzanos, G., Papafili, I., Seufert, M.: Trade-Off between QoE and Operational Cost in Edge Resource Supported Video Streaming.10th International Conference on P2P, Parallel, Grid, Cloud and Internet Computing (3PGCIC). , Krakow, Poland (2015).
The largest share of today`s consumer Internet traffic is video streaming and its demand on content delivery networks is continuously growing. To cope with the increasing demand of video streaming, recent work proposes mitigating end-user equipment to support content delivery at the edge of the network. The throughput of end-user equipment supporting content delivery is limited by the uplink of the users Internet connection.Especially for video streaming insufficient throughput causes the video to stall and affects the Quality of Experience (QoE) of end-users.To prevent video streams from stalling, we consider a tiered caching architecture, which requests higher tier caches to support content delivery, if the uplink throughput drops below a certain threshold. We conduct a simulative performance evaluation of the mechanism to investigate its impact on the QoE of end-users. Our results show that especially if the upload bandwidth of end-user equipment is low the setting of the threshold has a high impact. This can be used by operators to achieve the desired trade-off between QoE and operational cost for cache resources.
Hoßfeld, T., Moldovan, C., Schwartz, C.: To Each According to his Needs: Dimensioning Video Buffer for Specific User Profiles and Behavior.Third IFIP/IEEE International Workshop on Quality of Experience Centric Management. , Ottawa, Canada (2015).
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.
Casas, P., Schatz, R., Wamser, F., Seufert, M., Irmer, R.: Exploring QoE in Cellular Networks: How Much Bandwidth do you Need for Popular Smartphone Apps?5th ACM SIGCOMM Workshop on All Things Cellular: Operations, Applications and Challenges. , London, UK (2015).
A quarter of the world population will be using smartphones to access the Internet in the near future. In this context, understanding the Quality of Experience (QoE) of popular services in such devices becomes paramount for cellular network operators, who need to offer high quality levels to reduce the risks of customers churning for quality dissatisfaction. In this paper we study the problemof QoE provisioning in smartphones, presenting the results obtained from subjective lab tests performed for five popular apps: YouTube, Facebook, Web browsing through Chrome, Google Maps, and WhatsApp. The analysis addresses the impact of the access downlink bandwidth on the QoE of these apps when accessed through smartphones. The results presented in this paper provide a sound basis for better understanding the QoE requirements of popular services and mobile apps, as well as for dimensioning the underlying provisioning network. To the best of our knowledge, this is the first paper providing such a comprehensive analysis of QoE in mobile devices.
Lebreton, P., Mäki, T., Skodras, E., Hupont Torres, I., Hirth, M.: Bridging the Gap Between Eye Tracking and Crowdsourcing.SPIE 9394, Human Vision and Electronic Imaging XX. , San Francisco, USA (2015).
Visual attention studies aim at understanding how people scan images or videos. However, these types of studies require dedicated equipment such as IR-based eye trackers, which can be highly expensive. Moreover, one of the challenges with visual attention studies is that they require a large amount of tests to go beyond individuals. They are time consuming, may be intrusive and require specific setup that can be only obtained in a laboratory environment. This paper proposes a novel framework enabling crowd-sourced eye tracking tests using a standard web-cam and web-based techniques, to collect visual attention information from the users while interacting with the contents in ecologically valid environments. The performance of the preliminary user tests is promising and paves the way for low-cost universal eye tracking.
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.
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).
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.
Lareida, A., Petropoulos, G., Burger, V., Seufert, M., Soursos, S., Stiller, B.: Augmenting Home Routers for Socially-Aware Traffic Management.40th Annual IEEE Conference on Local Computer Networks (LCN). , Clearwater Beach, FL, USA (2015).
Mobile users' Quality-of-Experience (QoE) is degrading as network usage increases while Internet Service Providers (ISP) face increased inter-domain traffic. This paper presents a network traffic management mechanism, named RB-HORST, addressing these inefficiencies. RB-HORST exploits home routers by using them as caches and forming an overlay network between them to transfer content. To shift traffic from peak hours, RB-HORST employs predictions based on social network properties and based on similarity in the overlay network. To further improve user QoE, home routers allow trusted mobile devices to offload their mobile connection to the local WiFi. Simulation results show that an overlay is imperative for the success of the proposed caching mechanism. Especially ISPs with a large number of customers can benefit if only every thousandth user shares its router, reducing inter-domain traffic by half and superseding an ISP operated cache. The presented implementation proves that the concept is technically feasible and can be deployed and run on constrained devices.
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.
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.
Zinner, T., Lemmerich, F., Schwarzmann, S., Hirth, M., Karg, P., Hotho, A.: Text Categorization for Deriving the Application Quality in Enterprises using Ticketing Systems.17th International Conference on Big Data Analytics and Knowledge Discovery (DaWaK 2015). , Valencia, Spain (2015).
Today’s enterprise services and business applications are of- ten centralized in a small number of data centers. Employees located at branches and side offices access the computing infrastructure via the internet using thin client architectures. The task to provide a good application quality to the employers using a multitude of different applications and access networks has thus become complex. Enterprises have to be able to identify resource bottlenecks and applications with a poor performance quickly to take appropriate countermeasures and enable a good application quality for their employees. Ticketing systems within an enterprise use large databases for collecting complaints and problems of the users over a long period of time and thus are an interesting starting point to identify performance problems. However, manual categorization of tickets comes with a high workload. In this paper, we analyze in a case study the applicability of supervised learning algorithms for the automatic identification of relevant tickets, i.e., tickets indicating problematic applications. In that regard, we evaluate different classification algorithms using 12,000 manually annotated tickets accumulated in July 2013 at the ticketing system of a nation- wide operating enterprise. In addition to traditional machine learning metrics, we also analyze the performance of the different classifiers on business-relevant metrics.
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.
Lebreton, P., Hupont Torres, I., Mäki, T., Skodras, E., Hirth, M.: Eye Tracker in the Wild: Studying the Delta Between What is Said and Measured in a Crowdsourcing Experiment.Workshop on Crowdsourcing for Multimedia (CrowdMM). , Brisbane, Australia (2015).
Self-reported metrics collected in crowdsourcing experiments do not always match the actual user behaviour. Therefore in the laboratory studies the visual attention, the capability of humans to selectively process the visual information with which they are confronted, is traditionally measured by means of eye trackers. Visual attention has not been typically considered in crowdsourcing environments, mainly because of the requirements of specific hardware and challenging gaze calibration. This paper proposes the use of a non- intrusive eye tracking crowdsourcing framework, where the only technical requirements from the users’ side are a web- cam and a HTML5 compatible web browser, to study the differences between what a participant implicitly and explicitly does during a crowdsourcing experiment. To demonstrate the feasibility of this approach, an exemplary crowdsourcing campaign was launched to collect and compare both eye tracking data and self-reported metrics from the users. Participants performed a movie selection task, where they were asked about the main reasons motivating them to choose a particular movie. Results demonstrate the added value of monitoring gaze in crowdsourcing contexts: consciously or not, users behave differently than what they report through questionnaires.
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.
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.
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.
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.
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.
Ickin, S., Zinner, T., Wac, K., Fiedler, M.: Catching the Download Train: Energy-efficient File Downloading On Smartphones.Workshop on End-to-end Green Cellular Networks (Proceedings of 26th ITC Teletraffic Conference). , Karlskrona (2014).
Egger, S., Gardlo, B., Seufert, M., Schatz, R.: The Impact of Adaptation Strategies on Perceived Quality of HTTP Adaptive Streaming.1st Workshop on Design, Quality and Deployment of Adaptive Video Streaming (VideoNext). , Sydney, Australia (2014).
Changing network conditions like bandwidth fluctuations and resulting bad user experience issues (e.g. video freezes) pose severe challenges to Internet video streaming. To address this problem, an increasing number of video services utilizes HTTP adaptive streaming (HAS). HAS enables service providers to improve Quality of Experience (QoE) and resource utilization by incorporating information from different layers. However, these adaptation possibilities of HAS also introduce new perceivable impairments such as the fluctuation of audiovisual quality levels over time, which in turn lead to novel QoE-related research questions.The main contribution of this paper is the formulation of open research questions as well as a thorough systematic user-centric analysis of different quality adaptation dimensions and strategies. The underlying data has been acquired through two crowdsourcing and one lab study. The results provide guidance w.r.t. which encoding dimensions are combined best for the creation of the adaptation set and what type of adaptation strategy should be used. Furthermore it provides insights on the impact of adaptation frequency and the true QoE gain of adaptation over stallings.
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).
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.
Hoßfeld, T., Seufert, M., Sieber, C., Zinner, T.: Assessing Effect Sizes of Influence Factors Towards a QoE Model for HTTP Adaptive Streaming.6th International Workshop on Quality of Multimedia Experience (QoMEX). , Singapore (2014).
HTTP Adaptive Streaming (HAS) is employed by more and more video streaming services in the Internet. It allows to adapt the downloaded video quality to the current network conditions, and thus, avoids stalling (i.e., playback interruptions) to the greatest possible extend. The adaptation of video streams is done by switching between different quality representation levels, which influences the user perceived quality of the video stream. In this work, the influence of several adaptation parameters, namely, switch amplitude (i.e., quality level difference), switching frequency, and recency effects, on Quality of Experience (QoE) is investigated. Therefore, crowdsourcing experiments were conducted in order to collect subjective ratings for different adaptation-related test conditions. The results of these subjective studies indicate the influence of the adaptation parameters, and based on these findings a simplified QoE model for HAS is presented, which only relies on the switch amplitude and the playback time of each layer.
Hoßfeld, T., Hirth, M., Korshunov, P., Hanhart, P., Gardlo, B., Keimel, C., Timmerer, C.: Survey of Web-based Crowdsourcing Frameworks for Subjective Quality Assessment.16th International Workshop on Multimedia Signal Processing. , Jakarta, Indonesia (2014).
The popularity of the crowdsourcing for performing various tasks online increased significantly in the past few years. The low cost and flexibility of crowdsourcing, in particular, attracted researchers in the field of subjective multimedia evaluations and Quality of Experience (QoE). Since online assessment of multimedia content is challenging, several dedicated frameworks were created to aid in the designing of the tests, including the support of the testing methodologies like ACR, DCR, and PC, setting up the tasks, training sessions, screening of the subjects, and storage of the resulted data. In this paper, we focus on the web-based frameworks for multimedia quality assessments that support commonly used crowdsourcing platforms such as Amazon Mechanical Turk and Microworkers. We provide a detailed overview of the crowdsourcing frameworks and evaluate them to aid researchers in the field of QoE assessment in the selection of frameworks and crowdsourcing platforms that are adequate for their experiments.
Schwarzmann, S., Zinner, T., Hirth, M.: Deriving the Employee-perceived Application Quality in Enterprise IT Infrastructures using Information from Ticketing Systems.Workshop on Knowledge Discovery, Data Mining and Machine Learning (KDML 2014). , Aachen, Germany (2014).
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.
Oechsner, S., Bellalta, B., Dimitrova, D., Hoßfeld, T.: Visions and Challenges for Sensor Network Collaboration in the Cloud.The Eighth International Conference on Innovative Mobile and Internet Services in Ubiquitous Computing (IMIS-2014). , Birmingham, UK (2014).
The rapid growth in sensor network coverage, aided by the use of smartphones as capable sensing devices, leads to an enormous amount of gathered data from a multitude of different sources. However, generally data from one specific sensor network is only used by a very limited set of users and applications. This wastes a potentially greater usefulness for other, related data sinks that could use this additional input to improve their performance or services. In this paper, we outline visions and challenges for a widespread application of sensor network collaboration in the sense of sharing and exchanging information. We also describe a basic cloud-based architecture enabling this collaboration by providing the required support to store, manage and combine the gathered data. In particular, we include collaboration between sensor networks themselves to optimize performance, a facet that was up to now neglected in literature.
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.
Hupont, I., Lebreton, P., Mäki, T., Skodras, E., Hirth, M.: Is affective crowdsourcing reliable?5th International Conference on Communications and Electronics (ICCE 2014). , Da Nang, Vietnam (2014).
Affective content annotations are typically acquired from subjective manual assessments by experts in supervised laboratory tests. While well manageable, such campaigns are expensive, time-consuming and results may not be generalizable to larger audiences. Crowdsourcing constitutes a promising approach for quickly collecting data with wide demographic scope and reasonable costs. Undeniably, affective crowdsourcing is particularly challenging in the sense that it attempts to collect subjective perceptions from humans with different cultures, languages, knowledge background, etc. In this study we analyze the validity of well-known user affective scales in a crowdsourcing context by comparing results with the ones obtained in laboratory tests. Experimental results demonstrate that pictorial scales possess promising features for affective crowdsourcing.
Hoßfeld, T., Schatz, R., Krieger, U.: QoE of YouTube Video Streaming for Current Internet Transport Protocols.Measurement, Modelling and Evaluation of Computing Systems (MMB 2014). , Bamberg, Germany (2014).
Video streaming currently dominates global Internet traffic and will be of even increasing importance in the future. In this paper we assess the impact of the underlying transport protocol on the user perceived quality for video streaming using YouTube as example. In particular, we investigate whether UDP or TCP fits better for Video-on-Demand delivery from the end user's perspective, when the video is transmitted over a bottleneck link. For UDP based streaming, the bottleneck link results in spatial and temporal video artifacts, decreasing the video quality. In contrast, in the case of TCP based streaming, the displayed content itself is not disturbed but playback suffers from stalling due to rebufferung. The results of subjective user studies for both scenarios are analyzed in order to assess the transport protocol influences on Quality of Experience of YouTube. To this end, application-level measurements are conducted for YouTube streaming over a network bottleneck in order to develop models for realistic stalling patterns. Furthermore, mapping functions are derived that accurately describe the relationship between network-level impairments and QoE for both protocols.
Burger, V., Hirth, M., Schwartz, C., Hoßfeld, T.: Increasing the Coverage of Vantage Points in Distributed Active Network Measurements by Crowdsourcing.Measurement, Modelling and Evaluation of Computing Systems (MMB 2014). , Bamberg, Germany (2014).
Internet video constitutes more than half of all consumer traffic. Most of the video traffic is delivered by content delivery networks (CDNs). The huge amount of traffic from video CDNs poses problems to access providers. To understand and monitor the impact of video traffic on access networks and the topology of CDNs, distributed active measurements are needed. Recently used measurement platforms are mainly hosted in National Research and Education Networks (NRENs). However, the view of these platforms on the CDN is very limited, since the coverage of NRENs is low in developing countries. Furthermore campus networks do not reflect the characteristics of end user access networks. We propose to use crowdsourcing to increase the coverage of vantage points in distributed active network measurements. In this study, we compare measurements of a global CDN conducted in PlanetLab with measurements assigned to workers of a crowdsourcing platform. Therewith, the coverage of vantage points and the sampled part of the global video CDN are analyzed. Our results show that the capability of PlanetLab to measure global CDNs is rather low, since the vast majority of requests is directed to the US. By using the crowdsourcing platform we obtain a diverse set of vantage points that reveals more than twice as many autonomous systems deploying video servers.
Papafili, I., Wajda, K., Lapacz, R., Predieri, A., Bocek, T., Seufert, M.: An Overview of Application Traffic Management Approaches: Challenges and Potential Extensions.8th International Conference on Innovative Mobile and Internet Services in Ubiquitous Computing (IMIS). , Birmingham, UK (2014).
The Internet has seen a strong move to support overlay applications and services, which demand a coherent and integrated control in underlying heterogeneous networks in a scalable, resilient, and energy-efficient manner. To do so, a tighter integration of network management and overlay service functionality can lead to cross-layer optimization of operations and management, which is a promising approach and may offer a large business potential in operational perspectives for all players involved. Therefore, the objective of this paper is to present and discuss the impact of new paradigms such as cloud computing and software-defined networking which will play central role in the Future Internet, discuss major traffic trends and identify key challenges due to the adoption and operation of the new applications. Translating the key challenges to requirements for Future Internet traffic management mechanisms, the paper provides an extensive overview of existing mechanisms in literature, assesses them w.r.t. the aforementioned requirements, and qualitatively estimates the expected optimization potential and gain, as well as provides hint for their potential extension and exploitation within the challenging environment of the Future Internet.
Gardlo, B., Egger, S., Seufert, M., Schatz, R.: Crowdsourcing 2.0: Enhancing Execution Speed and Reliability of Web-based QoE Testing.IEEE International Conference on Communications (ICC). , Sydney, Australia (2014).
Since its introduction a few years ago, the concept of 'Crowdsourcing' has been heralded as highly attractive alternative approach towards evaluating the Quality of Experience (QoE) of networked multimedia services. The main reason is that, in comparison to traditional laboratory-based subjective quality testing, crowd-based QoE assessment over the Internet promises to be not only much more cost-effective (no lab facilities required, less cost per subject) but also much faster in terms of shorter campaign setup and turnaround times. However, the reliability of remote test subjects and consequently, the trustworthiness of study results is still an issue that prevents the widespread adoption of crowd-based QoE testing. Various ideas for improving user rating reliability and test efficiency have been proposed, with the majority of them relying on a posteriori analysis of results. However, such methods introduce a major lag that significantly affects efficiency of campaign execution. In this paper we address these shortcomings by introducing in momento methods for crowdsourced video QoE assessment, which yield improvements of results reliability by the factor two and campaign execution efficiency by the factor ten. The proposed in momento methods are applicable to existing crowd-based QoE testing approaches and suitable for a variety of service scenarios.
Zinner, T., Jarschel, M., Blenk, A., Wamser, F., Kellerer, W.: Dynamic Application-Aware Resource Management Using Software-Defined Networking: Implementation Prospects and Challenges.IFIP/IEEE International Workshop on Quality of Experience Centric Management (QCMan). , Krakow, Poland (2014).
Today’s Internet does not provide an exchange of information between applications and networks, which may result in poor application performance. Concepts such as applicationaware networking or network-aware application programming try to overcome these limitations. The introduction of Software- Defined Networking (SDN) opens a path towards the realization of an enhanced interaction between networks and applications. Hence, a more dynamic and demand-based allocation of network resources to heterogeneous applications can be realized. The implementation of the resource management action, however, may have an impact on the data transport and application quality. This paper summarizes resource management mechanisms provided by current SDN approaches based on OpenFlow and exemplary evaluates implementation prospects and challenges.
Metzger, F., Schwartz, C., Hoßfeld, T.: GTP-based Load Model and Virtualization Gain for a Mobile Network's GGSN.5th International Conference on Communications and Electronics. , Da Nang, Vietnam (2014).
Multiple outages in major mobile networks have been reported in the recent past. In fixed and datacenter networks, such capacity problems are solved by scaling out, i.e. purchasing additional hardware. In mobile networks this is not easily possible as network components are usually sold as sealed middleboxes. With the advances in server performance and SDN it has been suggested to virtualize these boxes. This also opens up opportunities to dimension according to current load and save energy by switching off parts of the infrastructure. Such suggestions immediately raise the question on the cost of virtualization. To answer this question, we introduce models for both a traditional as well as a virtualized GGSN. In addition, we provide distributions for the load experienced at the GGSN based on network measurements. With this at hand, we study the influence of different dimensioning parameters on important performance metrics, with special consideration for the impact of provisioning new instances for the virtual GGSN.
Wajda, K., Stankiewicz, R., Dulinski, Z., Hoßfeld, T., Seufert, M., Hausheer, D., Wichtlhuber, M., Papafili, I., Dramitinos, M., Cruschelli, P., Soursos, S., Lapacz, R., Stiller, B.: Socially-aware Management of New Overlay Applications Traffic - The Optimization Potentials of the SmartenIT Approach.6th International Conference on Mobile Networks and Management (MONAMI). , Würzburg, Germany (2014).
Today`s overlay-based mobile cloud applications determine a challenge to operators and cloud providers in terms of increasing traffic demands and energy costs. The social-aware management of overlay traffic is a promising optimization approach, which shows potential for improvements by exploiting social information. This paper identifies key stakeholders and their roles in the service provisioning value chain and outlines major markets and optimization potentials. Accordingly, two scenarios are developed: the end user focused scenario aming at increased QoE for end users, and the operator focused scenario targeting at the highest operating efficiency in terms of low cost and high revenue for the operator. The energy efficiency plays a major role as a key performance metric in both scenarios. SmartenIT`s socially-aware management approach is illustrated based on two example mechanisms for traffic optimization: the home router sharing mechanism (HORST) on the end user side, as well as the dynamic traffic management mechanism (DTM) on the operator side. The paper is concluded by a first sketch of SmartenIT`s architecture and its mapping to the two scenarios.
Seufert, M., Slanina, M., Egger, S., Kottkamp, M.: To Pool or not to Pool: A Comparison of Temporal Pooling Methods for HTTP Adaptive Video Streaming.5th International Workshop on Quality of Multimedia Experience (QoMEX). , Klagenfurt, Austria (2013).
Current objective video quality metrics typically estimate video quality for short video sequences (10 to 15 sec) of constant quality. However, customers of video services typically watch longer sequences of videos which are more and more delivered via adaptive streaming methods such as HTTP adaptive streaming (HAS). Typically a viewing session in such a setting contains several different video qualities over time. In order to express this in an overall score for the whole viewing session several temporal pooling methods have been proposed in the related work. Within this paper we set out to compare the performance of different temporal pooling methods for the prediction of Quality of Experience (QoE) for HTTP video streams with varying qualities. We perform this comparison based on ground truth rating data gathered in a crowdsourcing study in the context of the NGMN P-SERQU project. As input data for the models we use bjective video quality metrics such as PSNR, SSIM but also very basic inputs such as the bitrate of the clips only. Our results show that certain pooling methods perform clearly better than others. These results can help in identifying well performing temporal pooling methods in the context of HAS.
Seufert, M., Darzanos, G., Burger, V., Papafili, I., Hoßfeld, T.: Socially-Aware Traffic Management.Workshop Sozioinformatik. , Koblenz, Germany (2013).
Socially-aware traffic management exploits social signals to optimize traffic management in the Internet in terms of traffic load, energy consumption, or end-user satisfaction. Several use cases can benefit from socially-aware traffic management and the performance of overlay applications can be enhanced. In the talk we show interdisciplinary efforts between communication networks and social network analysis. Specifically, we give an overview on existing use cases and solutions, but also raise discussions at the workshop on additional benefits from the integration of social information into traffic management.
Seufert, M., Burger, V., Hoßfeld, T.: HORST - Home Router Sharing based on Trust.Workshop on Social-aware Economic Traffic Management for Overlay and Cloud Applications (SETM). , Zurich, Switzerland (2013).
Today’s Internet services are increasingly accessed from mobile devices, thus being responsible for growing load in mobile networks. At the same time, more and more WiFi routers are deployed such that a dense coverage of WiFi is available. Results from different related works suggest that there is a high potential of reducing load on the mobile networks by offloading data to WiFi networks, thereby improving mobile users’ quality of experience (QoE) with Internet services. Additionally, the storage of the router could be used for content caching and delivery close to the end user, which is more energy efficient compared to classical content servers, and saves costs for network operators by reducing traffic between autonomous systems. Going one step beyond, we foresee that merging these approaches and augmenting them with social information from online social networks (OSNs) will result both in even less costs for network operators and increased QoE of end users. Therefore, we propose home router sharing based on trust (HORST) - a socially-aware traffic management solution which targets three popular use cases: data offloading to WiFi, content caching/prefetching, and content delivery.
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.
Klein, D., Zinner, T., Borchert, K., Lange, S., Singeorzan, V., Schmid, M.: Evaluation of Video Quality Monitoring based on Pre-computed Frame Distortions.19th EUNICE Workshop on Advances in Communication Networking, Best Paper Award. , Chemnitz, Germany (2013).
A large fraction of the current Internet traffic is caused by video streaming. Due to the growing expectations of video consumers, monitoring video applications is getting more and more important for network and service providers. In a previous work, we proposed a video quality monitoring solution which utilizes the full reference SSIM metric to improve the monitoring in the network by distributing pre-computed distortion information induced by frame losses. To improve scalability, we introduced a less complex algorithm which infers the distortion for higher loss scenarios from single loss scenarios and inter-frame dependencies. In this work, we evaluate the accuracy of our algorithm by comparing it with the exact calculation of the SSIM metric for different frame loss scenarios. We further consider different high definition test video sequences and group of picture structures and investigate the influence on the accuracy of our proposed approximation.
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.
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.
Seufert, M., Lorey, K., Hirth, M., Hoßfeld, T.: Gamification Framework for Personalized Surveys on Relationships in Online Social Networks.1st International Workshop on Crowdsourcing and Gamification in the Cloud (CGCloud). , Dresden, Germany (2013).
The estimation of psychological properties of relationships (e.g., popularity, influence, or trust) only from objective data in online social networks (OSNs) is a rather vague approach. A subjective assessment produces more accurate results, but it requires very complex and cumbersome surveys. The key contribution of this paper is a framework for personalized surveys on relationships in OSNs which follows a gamification approach. A game was developed and integrated into Facebook as an app, which makes it possible to obtain subjective ratings of users' relationships and objective data about the users, their interactions, and their social network. The combination of both subjective and objective data facilitates a deeper understanding of the psychological properties of relationships in OSNs, and lays the foundations for future research of subjective aspects within OSNs.
Hoßfeld, T., Strohmeier, D., Raake, A., Schatz, R.: Pippi Longstocking Calculus for Temporal Stimuli Pattern on YouTube QoE.5th ACM Workshop on Mobile Video (MoVid 2013). , Oslo, Norway (2013).
Video streaming over wireless broadband is currently re- sponsible for half of the world-wide mobile data traffic and its share is expected to even further increase. Therefore, mobile operators need to understand how Quality of Ex- perience (QoE) of mobile video streaming is impacted by through the network delivery. Due to HTTP video stream- ing used by video portals like YouTube or NetFlix, problems or insufficient resources in the networks manifest as stalling events during service consumption on an end user device. In this paper, we discuss the challenges for QoE monitoring for HTTP-based mobile video regarding three aspects. First, the impact of different patterns in terms of stalling event frequency and length on QoE is quantified on behalf of a study on YouTube. Second, we evaluate predictive power of aggregate measures like total stalling time. Third, we discuss the resulting consequences and challenges for mobile video QoE modeling, monitoring and provisioning.
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.
Burger, V., Hoßfeld, T., Garcia, D., Seufert, M., Scholtes, I., Hock, D.: Resilience in Enterprise Social Networks.Workshop Sozioinformatik 2013. , Koblenz, Germany (2013).
The goal of human resource management is to ensure an effective company environment. Crucial for a good corporate culture is a comfortable atmosphere and positive social relationships between the employees. The interactions of the people and groups working in the company define their relationships and are reflected in the company's social network. Projections of such networks are Enterprise Social Networks which are more and more integrated in companies. These social networks can be a powerful tool to analyse the structure of a company and indicate potential problems. This extended abstract poses research questions to identify and quantify mechanisms that have an impact on the social network of a company to ensure resilience. To address these questions we make assumptions based on real-world observations for a subsequent model.
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.
Casas, P., Schatz, R., Hoßfeld, T.: Monitoring YouTube QoE: Is Your Mobile Network Delivering the Right Experience to your Customers?2013 IEEE Wireless Communications and Networking Conference (WCNC 2013). , Shanghai, China (2013).
YouTube, the monster application of today’s Internet, is changing the way ISPs and network operators manage quality monitoring and provisioning on their IP networks. YouTube is currently the most consumed Internet application, accounting for more than 30% of the overall Internet’s traffic worldwide. Coupling such an overwhelming traffic volume with the ever intensifying competition among ISPs is pushing operators to integrate Quality of Experience (QoE) paradigms into their traffic management systems. The need for automatic QoE assessment solutions becomes even more critical in mobile broadband networks, where over-provisioning solutions can not be foreseen and bad user experience translates into churning clients. This paper presents a complete study on the problem of YouTube Quality of Experience monitoring and assessment in mobile networks. The paper considers not only the QoE analysis, modeling and assessment based on real users’ experience, but also the passive monitoring of the quality provided by the ISP to its end-customers in a large mobile broadband network.
Varela, M., Mäki, T., Skorin-Kapov, L., Hoßfeld, T.: Increasing Payments in Crowdsourcing: Don't look a gift horse in the mouth.4th International Workshop on Perceptual Quality of Systems (PQS 2013). , Vienna, Austria (2013).
A commonly cited maxim states that 'you get what you pay for'. Implicit in it is the idea that there is a strong correlation between the price paid for something, and its quality. In this paper, we examine whether that applies to crowdsourcing for QoE experiments, and if so, how. As part of a large-scale Web QoE experiment, we conducted two crowdsourced campaigns to try and understand the influence of certain website design parameters related to typography and color on the overall visual appeal of the site. The second campaign was set up to pay three times the reward of the first one. We analyze the impact of payment on a number of parameters, including ratio of reliable users and obtained MOS values, and provide recommendations for QoE modeling.
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.
Casas, P., Seufert, M., Schatz, R.: YOUQMON: A System for On-line Monitoring of YouTube QoE in Operational 3G Networks.31st International Symposium on Computer Performance, Modeling, Measurements and Evaluation (IFIP Performance). , Vienna, Austria (2013).
YouTube is changing the way operators manage network performance monitoring. In this paper we present YOUQMON, a novel on-line monitoring system for assessing the Quality of Experience (QoE) undergone by HSPA/3G users watching YouTube videos, using network-layer measurements only. YOUQMON combines passive traffic analysis techniques to detect stalling events in YouTube video streams, with a QoE model to map stallings into a Mean Opinion Score reflecting the end-user experience. We evaluate the stalling detection performance of YOUQMON with hundreds of YouTube video streams, and present results showing the feasibility of performing real-time YouTube QoE monitoring in an operational mobile broadband network.
Inführ, J., Stezenbach, D., Hartmann, M., Tutschku, K., Raidl, G.R.: Using Optimized Virtual Network Embedding for Network Dimensioning.IEEE Conference on Networked Systems (NetSys) 2013. , Stuttgart, Germany (2013).
Virtual Network Embedding will be one of the key concepts of the Future Internet. For an ISP it is important to know how many additional Virtual Networks (VNs) of a specific application (e.g. web, streaming, P2P, and VoIP) are mappable into the current resource substrate with a certain probability. In this work we calculate this probability with our embedding algorithm which enables us to consider side effects based on remapping of VNs (e.g. due to reduced link delay). Our results show that minimal extra resources can significantly increase embedding probability of additional VNs.
Klein, D., Jarschel, M.: An OpenFlow Extension for the OMNeT++ INET Framework.6th International Workshop on OMNeT++. , Cannes, France (2013).
Software Defined Networking (SDN) is a new paradigm for communication networks which separates the control plane from the data plane of forwarding elements. This way, SDN constitutes a flexible architecture that allows quick and easy configuration of network devices. This ability is particularly useful when networks have to be adapted to changing traffic volumes of different applications running on the network. OpenFlow is currently the most prominent approach which implements the SDN concept and offers a high flexibility in the routing of network flows. In this paper, we describe the implementation of our model of the OpenFlow system in the INET framework for OMNeT++. We present performance results to show the correctness of our model. As a first application, we use the simulation model to assess the round-trip-times in a theoretical OpenFlow deployment in a real topology of a North-American Testbed.
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.
Klein, D., Zinner, T., Lange, S., Singeorzan, V., Schmid, M.: Video Quality Monitoring based on Precomputed Frame Distortions.IFIP/IEEE International Workshop on Quality of Experience Centric Management (QCMan). , Ghent, Belgium (2013).
In the past decade, video streaming has taken over a large part of the current Internet traffic and more and more TV broadcasters and network providers extend their portfolio of video streaming services. With the growing expectations of video consumers with respect to the service quality, monitoring is an important aspect for network providers to detect possible performance problems or high network load. In parallel, emerging technologies like software defined networking or network virtualization introduce support for specialized networks which allow enhanced functionality in the network. This development enables more sophisticated monitoring techniques in the specialized networks which use knowledge about the video content to better predict the service quality at consumers. In this work, we present a content-aware SSIM-based monitoring technique and compare it with the current state-of-the art which infers the service quality from the monitored packet loss. We further show how network conditions like packet loss or bursts influence the two different monitoring techniques.
Casas, P., Seufert, M., Egger, S., Schatz, R.: Quality of Experience in Remote Virtual Desktop Services.IFIP/IEEE International Workshop on Quality of Experience Centric Management (QCMan). , Ghent, Belgium (2013).
Remote Virtual Desktop (RVD) services provide flexible and cost-effective means to deliver virtual PCs to end-users. RVD services have been traditionally deployed in enterprise LAN scenarios, where network performance is optimal and the Quality of Experience (QoE) undergone by its users is generally not an issue. However, the need for mobility of RVD users (e.g., remote office, home office, etc.) and the explosion of Cloud-based services have pushed RVD to WAN scenarios, and nowadays it is common to find RVD services running at large datacenters in the Cloud. In such a context, network delay and bandwidth are very dynamic and difficult to guarantee or even to control, and QoE becomes a real bottleneck. In this paper we present a complete study of the QoE undergone by 52 RVD users in controlled subjective lab tests. The study is performed on a dedicated RVD testbed based on Citrix technology, which is the de-facto RVD solution used in enterprise scenarios. The study permits not only to better understand the interplays between network performance (i.e., network delay and bandwidth) and QoE in RVD services, but also provides results on the behavior of RVD users when confronted to variable network conditions w.r.t. their behavior on standard local desktops.
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.
Sackl, A., Seufert, M., Hoßfeld, T.: Asking Costs Little? The Impact of Tasks in Video QoE Studies on User Behavior and User Ratings.4th International Workshop on Perceptual Quality of Systems (PQS). , Vienna, Austria (2013).
Three crowdsourcing video QoE studies have been conducted to investigate the influence of tasks on user behavior and quality perception. Different dimensions of tasks have been applied to impaired video clips and their impact on task success, focus time, and QoE was measured. Our findings suggest that task presence or absence has no influence on the user. However, continuous tasks can improve the focus times of users, and hard tasks are suitable to filter unreliable participants.
Varela, M., Mäki, T., Skorin-Kapov, L., Hoßfeld, T.: Towards an understanding of visual appeal in website design.Fifth International Workshop on Quality of Multimedia Experience (QoMEX 2013). , Klagenfurt, Austria (2013).
Visual appeal (VA), as judged by users accessing different websites, has been shown to impact overall user preferences and satisfaction. In the context of Web Quality of Experience (QoE), we hypothesize that VA has a non-trivial impact on end user quality perception and hence needs to be accounted for when modeling overall Web QoE. In this paper, we aim to quantify the impact of VA factors on perceived visual design quality for different types of tested websites. We carried out two large-scale (>350 users each) crowd-sourced campaigns to test the influence of several factors often found in design best practices recommendations. While results have identified color goodness and font goodness as Key Influence Factors (KIF) for VA, an analysis of user demographics has further shown a strong impact of user's origin on subjective ratings. By quantifying the impact of identified KIFs on VA, we provide guidelines for successful VA manipulations to be considered in future Web QoE subjective tests.
Amrehn, P., Vandenbroucke, K., Hoßfeld, T., de Moor, K., Hirth, M., Schatz, R., Casas, P.: Need for Speed? On Quality of Experience for File Storage Services.4th International Workshop on Perceptual Quality of Systems (PQS 2013). , Vienna, Austria (2013).
Cloud computing has received a lot of attention within several research domains. However, there are only a few studies that focus on Quality of Experience (QoE) from a user perspective in the context of personal cloud storage services. In order to gain insights in existing use practices and to detect possible QoE influencing factors and relevant features, we conducted an online survey amongst users of personal cloud storage services and applications in general (N=349) and one specifically targeted at Dropbox users (N=49). Both studies point to accessibility, data sharing and data back-up as key features of personal cloud storage services. In addition, performance, i.e. upload and download speed, goes hand in hand with synchro-nization speed and should be taken into account when measur-ing QoE. However, cost, privacy and security related issues are as important factors as well.
Redi, J., Hoßfeld, T., Korshunov, P., Mazza, F., Povoa, I., Keimel, C.: Crowdsourcing-based multimedia subjective evaluations: a case study on image recognizability and aesthetic appeal.ACM CrowdMM 2013. , Barcelona, Spain (2013).
Crowdsourcing is a popular approach for employing people online to perform short and simple tasks. Research on Quality of Experience (QoE), which relies on subjective evaluations of media, could especially benefit from it. One question related to QoE, which is as well important for image retrieval and summarization systems, concerns modelling and quantifying the subjective notions of `beauty' (aesthetic appeal) and `something well-known' (content recognizability). Since both notions may be subject to cultural and social effects, crowdsourcing, which allows to employ worldwide, can be a great tool for carrying on subjective studies in a time and cost-effective way. On the other hand, the crowdsourcing environment does not allow for the degree of excperimental control which is necessary to guarantee reliable subjective data. In this paper, we evaluate aesthetic appeal and recognizability of images using a crowdsourcing platform and compare the outcomes with more conventional evaluations conducted in a controlled lab environment. We find high correlation between crowdsourcing and lab scores for recognizability but not for aesthetic appeal. The analysis of the results indicates possible causes for this, suggesting that crowdsourcing can be used for QoE subjective assessments as long as the workers' tasks are designed with extreme care to avoid misinterpretations and unreliability.
