Alberto Álvarez

Limitations of network emulation with single-machine and distributed ns-3

Research on large-scale internet services requires an extensive evaluation prior to deployment. A good analysis must include tests over large networks, using real devices and a considerable number of users. However, how to test in these scenarios with many users is an open question. Network emulation can be a good alternative before real deployments, which are complex and expensive. In this paper, we examine the new ns-3 network simulator/emulator in order to determine its capacity in the evaluation of large scale services. For that purpose, a real client/server video service is deployed over an emulated network. The service is progressively scaled up by increasing the number of clients on a single machine. In addition, we have extended ns-3 to support a distributed architecture for network nodes, thus, we repeat the experiments with a distributed set-up. Advantages, disadvantages, possibilities and limitations of both approaches are thoroughly discussed.

Subjective evaluation of critical success factors for a QoE aware adaptive system

For many years video content delivery has established itself as the killer application. Improving QoE on adaptive streaming is focusing many efforts in the quest for optimized methods and metrics to allow a QoE driven adaptation. Questions such as whether adaptive systems based on Scalable Video Coding improve subjective quality and in which situations or to what degree are still open issues. Tolerance and indifference thresholds for each type of content, conditions or viewer category, with regard to adaptive systems are critical success factors that are yet unresolved. We compare the performance of a complete adaptive system with the traditional, i.e. non-adaptive, approach in subjective terms. Results of surveying 75 participants show that the adaptation improves QoE under most of the evaluated conditions. Tolerance thresholds for triggering adaptation events have been identified. Users accustomed to Internet video are more critical than users that only watch TV. The under 35year old subset among the available population is generally more satisfied with the adaptive system than the older subset.

A flexible QoE framework for video streaming services

QoE metrics are a must in new service evaluations as they have shown to outperform traditional QoS. This work presents a flexible framework for measuring different types of QoE analysis and capable of synchronizing reference sequence with distorted videos for avoiding erroneous coupling. We define cPSNR metric, a measurement system suitable for performing the evaluation of transmission impairments exclusively, from the perceived quality perspective. The metric is validated with a subjective video database showing a promising correlation with both packet loss ratio and subjective quality.

In pursuit of massive service emulation: a methodology for testbed building

Every day, more services in the Internet (Youtube, Facebook, etc.) are being massively used, while network operators struggle to maintain their performance. Since simulations are not always accurate and evaluation prior to deployment is a must, it is often convenient to build an emulation testbed to test these services in more realistic environments. This methodology proposes four steps to guide researchers in this task. Before running the experiments and gathering results, it is necessary to specify the service under test, define the testbed requirements, and allocate the resources properly. For this reason, a set of techniques are proposed to solve the most common challenges at every step, such as adding real users or selecting the best simulation technique for our goals. The purpose is to efficiently employ the available resources without compromising the realism and accuracy of results. The application of the methodology to a case study, a high-quality audio and video on-demand service over a communication network, shows how resource constraints can be overcome to accomplish our goals.

Subjective video quality evaluation of different content types under different impairments

ABSTRACT Nowadays, access to multimedia content is one of the most demanded services on the Internet. However, the transmission of audio and video over these networks is not free of problems that negatively affect user experience. Factors such as low image quality, cuts during playback or losses of audio or video, among others, can occur and there is no clear idea about the level of distortion introduced in the perceived quality. For that reason, different impairments should be evaluated based on user opinions, with the aim of analyzing the impact in the perceived quality. In this work, we carried out a subjective evaluation of different types of impairments with different types of contents, including news, cartoons, sports and action movies. A total of 100 individuals, between the ages of 20 and 68, participated in the subjective study. Results show that short-term rebuffering events negatively affect the quality of experience and that desynchronization between audio and video is the least annoying impairment. Moreover, we found that the content type determines the subjective results according to the impairment present during the playback.

Service To Manage The Efficient Driving Of Combustion Vehicle Fleets To Support ISO 50001

The ISO 50001 is an international standard oriented to the energy management. In the transport sector and in companies where the equipment is mainly combustion engine means, this energy management process is principally oriented to control the vehicle fuel consumption. In this paper, we present a service capable of monitoring how and when the fuel is consumed and offering tools to the fleet responsible to analyze and manage it. The service produces the required information and tools to support the ISO 50001 certification. To evaluate its performance, the service has been deployed in several vehicles of a garbage collector company making possible a reduction in the fuel consumption by approximately 20%.

Limits for the real-time simulation of video services over commodity hardware

The results from event-driven simulations with video services can present limitations because of the cost of developing accurate models. Creating a video server model precise in how streams are transmitted is generally as expensive as the construction of the real server, thus several simplifications are generally introduced to reduce the effort. In this context, the lack of accuracy could be devastating if metrics such as jitter are imprecise. One potential alternative to solve these issues is the combination of real services with Real-Time (R-T) capable network simulators. This paper evaluates R-T simulation capabilities of two of the most popular tools, NS-3 and OPNET to support the performance evaluation of video services using a commodity hardware testbed. Taking a video on demand service as a test case, we have studied the use of NS-3 and OPNET in situations where their more profitable characteristics, such as instance creation simplicity or the use of analytic traffic, could produce the best results. The performed tests show how NS-3 is able to replicate an access network topology with up to 10 MPEG-4 video streams or OPNET has been able to replicate a ring core network with up to 60 of the same streams without affecting important metrics as important as jitter. These results point out the validity of R-T simulation in the context of services that have streams as a main component if their strengths are taken into account.

Runtime adaptability to domain model changes with efficient constraint checking

On November 27, 2015, Alberto Manuel FernándezÁlvarez defended his PhD thesis on Runtime adaptability to domain model changes with efficient constraint checking at the University of Oviedo. He presented his dissertation in a publicly open presentation held in the School of Computing (Fig. 1). After commenting on every question raised by the assessing committee, he was awarded the highest grade possible (cum laude). The thesis was supervised by Dr. Daniel FernándezLanvin and Dr. Raúl Izquierdo. The PhD dissertation Committee was composed of Professor Juan Manuel Cueva-Lovelle (University of Oviedo), Dr. J. Baltasar Garcia Perez-Schofield (University of Vigo), and Dr. Beatriz Pérez-Valle (University of La Rioja). This research work has been funded by the European Union, through the European Regional Development Funds (ERDF); and the Principality of Asturias, through its Science, Technology and Innovation Plan (grant GRUPIN14-100).

A Framework to Measure and Estimate Video Quality in SVC Real-Time Adaptive Systems

Effectively adapting the content to network conditions in real-time is an important matter in best-effort networks like the Internet. Scalable Video Coding (SVC) is an interesting alternative to implement such systems. However, some problems of the performance evaluation of SVC based adaptive systems have not been solved. The authors review the main efforts directed to measure video quality on SVC related systems and discuss the limitations of each one. This paper elaborates a framework to measure video quality metrics in real adaptive SVC based streams. An estimation method for full reference video quality metrics is proposed. This method reduces reference information required and it is able to provide real-time accurate results simply using metadata regarding the video quality of the reference layers. The video quality of several streams that have been generated using a real-time adaptive system is first measured with the elaborated framework and then estimated with the proposed method. A Framework to Measure and Estimate Video Quality in SVC Real-Time Adaptive Systems