Helmut Hlavacs

Energy Consumption of Residential and Professional Switches

Precise evaluation of network appliance energy consumption is necessary to accurately model or simulate the power consumption of distributed systems. In this paper we evaluate the influence of traffic onto the consumption of electrical power of four switches found in home and professional environments. First we describe our measurement and data analysis approach, and how our results can be used for estimating the power consumption when knowing the average traffic bandwidth.Then we present the measurement results of two residential switches, and two professional switches. For each type we present regression models and parameters describing their quality. Similar to other works we find that for one of the switches the power consumption actually drops for high traffic loads, while for the others the situation is reverse. Measures justify that during most energy consumption evaluation, network appliance energy cost can be approximated as constant. This work gives information on the possible changes of this cost.

Methodology of measurement for energy consumption of applications

For IT systems, energy awareness can be improved in two ways, (i) in a static or (ii) in a dynamic way. The first way leads to building energy efficient hardware that runs fast and consumes only a few watts. The second way consists of reacting to instantaneous power consumption, and of taking decisions that will reduce this consumption.

Cellular data meet vehicular traffic theory: location area updates and cell transitions for travel time estimation

Road traffic can be monitored by means of static sensors and derived from floating car data, i.e., reports from a sub-set of vehicles. These approaches suffer from a number of technical and economical limitations. Alternatively, we propose to leverage the mobile cellular network as a ubiquitous mobility sensor. We show how vehicle travel times and road congestion can be inferred from anonymized signaling data collected from a cellular mobile network. While other previous studies have considered data only from active devices, e.g., engaged in voice calls, our approach exploits also data from idle users resulting in an enormous gain in coverage and estimation accuracy. By validating our approach against four different traffic monitoring datasets collected on a sample highway over one month, we show that our method can detect congestions very accurately and in a timely manner.

Modeling user behavior: a layered approach

The simulation of computer systems requires representative, reliable workload models. When simulating computer systems or components that are influenced by user behavior, this very behavior has to be modeled by using mathematical means. In this article, we propose a user behavior model framework that is constructed in a top-down manner consisting of various layers. The layers offer services to the next higher layer and require services from the layers below. The framework is meant to enable the modeler to plug in his own models at the layers of his choice, thus choosing the right balance between the simulation complexity and creating representative results. We give a description of the layered framework and the corresponding methodology. The approach is then demonstrated on modeling HTTP traffic, to be used in network traffic simulation.

Is virtual reality emotionally arousing? Investigating five emotion inducing virtual park scenarios

Following the idea of using virtual environments (VEs) as mood induction procedures (MIPs), this study set out to examine whether five different virtual park scenarios would each elicit a specific affective state (i.e., joy, sadness, boredom, anger and anxiety). Within this main objective, a subset of two additional goals was identified: first, to analyze whether the sense of presence would differ across emotionally charged VEs, and second, to examine the link between a more objective measure of affective arousal, electrodermal activity (EDA), and presence. Following a between-subject design, 120 students were randomly assigned to one of the five VEs. Results show that almost all of the five virtual park scenarios were able to elicit the intended emotion. Additionally, presence levels were the same across all VEs suggesting that presence did not confound the emotional reaction to the VEs. Furthermore, EDA seems to be a poor indicator of presence as it is not significantly correlated with self-reported presence. The implications of these findings for both future research and practice are addressed in a comprehensive discussion. Four virtual park scenarios elicited the intended emotional states.Presence levels were the same across different virtual environments.Skin conductance level seems to be a poor indicator of presence.

Energy Consumption Side-Channel Attack at Virtual Machines in a Cloud

Virtualized data centers where several virtual machines (VMs) are hosted per server are becoming more popular due to Cloud Computing. As a consequence of energy efficiency concerns, the exact combination of VMs running on a specific server will most likely change over time. We present experimental results how to use the energy/power consumption logs of a power monitored server as a side-channel that allows us to recognize the exact combination of VMs it currently hosts to a high degree. For classification, we use a maximum log-likelihood approach, which works well for comparably small training and test set sizes. We also show to which degree a specific VM can be recognized, regardless of other VMs currently running on the same server, and show false negative/positive rates. To cross-validate our results, we have used a Kolmogorov-Smirnov test, resulting in comparable quality of recognition within shorter time. In order to clarify whether our approach is generalizable and yields reproducible results, we have set up a second experimental infrastructure in Lyon, using a different hardware platform and power measurement device. We have obtained similar results and have experimented with different CPU frequency scaling governors, yielding comparable quality of recognition. As a result, energy consumption data of servers must be protected carefully, as it is potentially valuable information for an attacker trying to track down a VM to mount further attack steps.

The Cellular Network as a Sensor: From Mobile Phone Data to Real-Time Road Traffic Monitoring

Mobile cellular networks can serve as ubiquitous sensors for physical mobility. We propose a method to infer vehicle travel times on highways and to detect road congestion in real-time, based solely on anonymized signaling data collected from a mobile cellular network. Most previous studies have considered data generated from mobile devices active in calls, namely Call Detail Records (CDR), an approach that limits the number of observable devices to a small fraction of the whole population. Our approach overcomes this drawback by exploiting the whole set of signaling events generated by both idle and active devices. While idle devices contribute with a large volume of spatially coarse-grained mobility data, active devices provide finer-grained spatial accuracy for a limited subset of devices. The combined use of data from idle and active devices improves congestion detection performance in terms of coverage, accuracy, and timeliness. We apply our method to real mobile signaling data obtained from an operational network during a one-month period on a sample highway segment in the proximity of a European city, and present an extensive validation study based on ground-truth obtained from a rich set of reference datasources - road sensor data, toll data, taxi floating car data, and radio broadcast messages.

Hierarchical video patching with optimal server bandwidth

Video patching is a way for transporting true video-on-demand, that is, instantaneous without any delay, from a video server to several clients. Instead of sending a unique stream to each newly arriving client, clients share as many multicast transmissions as possible, and are serviced only those parts of the video that they have missed. We present a novel video patching scheme using hierarchies of patches. Our scheme minimizes the bandwidth needed by the video server, and may result in the fact that clients receive several streams in parallel. We show analytically that for Poisson arrival our algorithm achieves the optimal possible server bandwidth for all schemes where clients share multicast transmissions. We also show, how our approach can be combined with batching. This combination requires less server bandwidth than all fixed start point periodic broadcast algorithms.

Physical and social presence in collaborative virtual environments: Exploring age and gender differences with respect to empathy

Collaborative virtual environments (CVEs) hold the immense potential of enhancing social inclusion and social support not only in younger but especially also in older people. However, there is still considerably little knowledge about the experiences of elderly when using CVEs. Additionally, there is reason to assume that men and women regardless of their age might also differ in their perceptions of CVEs, with this difference very likely being mediated by empathic abilities. Consequently, the main objective of the current study was to evaluate gender specific experiences of social and physical presence in a group of older (N=62) and younger adults (N=62) with respect to possible mediating influences of empathy. Results indicate no differences in physical and social presence between the two age groups, yet they support past findings that men experience more spatial presence, involvement and a higher sense of being there than women. Also, the empathy scale Fantasy considerably mediated gender differences in spatial presence, thus strengthening the theoretical assumption of a relationship between presence and empathy. Implications and future directions of these findings are discussed in detail.

A survey on user studies and technical aspects of mobile multimedia applications

Abstract Some years ago, Mobile TV has been introduced in several countries all over the world. It was expected that it would play a major role among traditional TV services. Unfortunately, the success has been limited at the beginning. Since Mobile TV brings new aspects into television, like small screens, consumption in noisy surroundings, etc., it also represents a new challenge on how to create, transfer and present content that maximizes the consumer experience. Today, some of these issues have been solved. Due to the introduction of smart phones and the large amount of available applications customers are starting to use their mobile phones for several purposes including mobile multimedia services. As a consequence, the concept for Mobile TV has changed significantly. In the past, research has often been focusing on one particular aspect of this new TV scheme, as well as surveys on this research often neglected aspects that still might be of interest when trying to understand the dependencies of Mobile TV content and presentation to perceived quality. In this survey paper we want to discuss challenges and requirements in a comprehensive way, trying to shed light on all relevant aspects of Mobile TV. The aim of this paper is to give a good overview about the state of the art with the focus of users’ need and experiences. A large collection of technical aspects and research results represents a special interest of this study. Finally, we want to discuss a framework for mobile multimedia applications which is relevant for further research work.