# Selected Publications

### Definition of QoE Fairness in Shared Systems

The contribution of this paper is the definition of a generic QoE fairness index $F$ which has desirable key properties as well as the rationale behind it. By using examples and a measurement study involving multiple users downloading web content over a bottleneck link, we differentiate the proposed index from QoS fairness and the widely used Jain’s fairness index. Based on results, we argue that neither QoS fairness nor Jain’s fairness index meet all of the desirable QoE-relevant properties which are met by $F$.
IEEE Communications Letters, vol. 21, no. 1, pp. 184-187

### QoE beyond the MOS: an in-depth look at QoE via better metrics and their relation to MOS

While Quality of Experience (QoE) has advanced very significantly as a field in recent years, the methods used for analyzing it have not always kept pace. When QoE is studied, measured or estimated, practically all the literature deals with the so-called Mean Opinion Score (MOS). In this article we put forward the limitations of MOS, present other statistical tools that provide a much more comprehensive view of how quality is perceived by the users, and illustrate it all by analyzing the results of several subjective studies with these tool
Quality and User Experience 1(1):1-23, Springer.

### From Service Level Agreements (SLA) to Experience Level Agreements (ELA): The Challenges of Selling QoE to the User

In this paper, we argue that the introduction of Experience Level Agreements (ELA) as QoE-enabled counterpiece to traditional QoS-based Service Level Agreements (SLA) would provide a key step towards being able to sell service quality to the user. Hence, we investigate various ideas to exploit QoE awareness for improving SLAs (ranging from internal aspects like SLOs by service providers to completely novel definitions of ELAs which are able to characterize QoE explicitly), and discuss important problems and challenges of the proposed transition as well.
In proceedings of IEEE ICC QoE-FI, London, UK.

### Meta-Modeling QoE — Towards a Generic Methodology for Building QoE Models

In this paper we propose a methodological framework for modeling Quality of Experience (QoE) for media services in a generic manner. We consider QoE as a multi-dimensional concept dependent on several factors related to the service itself, its resource requirements, its users, and its context of use.
In PIK - Praxis der Informationverarbeitung und -kommunikation, 37(4):265-274

### A Multi-Dimensional View of QoE: the ARCU Model

In this paper we present a generic ARCU (Application-Resource-Context-User) Model which categorizes influence factors into four multi-dimensional spaces. The model further maps points from these spaces to a multi-dimensional QoE space, representing both qualitative and quantitative QoE metrics.
In proceedings of MIPRO 2012, Opatija, Croatia.

### Challenges of QoE Management for Cloud Applications

In this article, we discuss technical challenges emerging from shifting services to the Cloud, as well as how this shift impacts QoE and QoE management.
IEEE Communications Magazine, 50(4):28-36

### Quality Assessment of Interactive Voice Applications

The conversational quality of a VoIP communication is dependent on several factors such as the coding process used, the network conditions and the type of error correction or concealment employed. Furthermore, the quality perceived by the users is also dependent on the characteristics of the conversation itself. In this paper we study the combined effects of bit rate, forward error correction, loss rate, loss distribution, delay and jitter on the perceived conversational quality.
Computer Networks 52(6):1179-1192.

### Performance Evaluation of Real-time Speech Through a Packet Network: a Random Neural Networks-based Approach

We propose a method for building real-time models for speech streams. Our method is based on using G-networks (open networks of queues with positive and negative customers) as Neural Networks (in this case, they are called Random Neural Networks) to learn, in some sense, how humans react vis-à-vis a speech signal that has been distorted by encoding and transmission impairments. We further apply our technique to study the impact on performance of several basic source and network parameters on a non-interactive speech flow, namely loss rate, loss distribution, codec, forward error correction, and packetization interval, all at the same time.
Performance Evaluation, 57(2):141-162

# Recent Publications

• Some Observations on Emerging Aspects in QoE Modeling and Their Impact on QoE Management

In proceedings of QoE-Management 2018, Sardinia, Italy.

• A Survey of Emerging Concepts and Challenges for QoE Management of Multimedia Services

In ACM Transactions on Multimedia Computing, Communications, and Applications (TOMM), special issue on QoE Management (Vol 14, Issue 2, May 2018)

Dagstuhl Perspectives Manifesto (Dagstuhl Perspectives Workshop 16472)

• What You Pay Is What You Get? — Fundamentals of Charging Internet Services Based on End User Quality of Experience

In Quality and User Experience (2018)3:5 — Springer

• QoE Analysis of the Setup of Different Internet Services for FIFO Server Systems

In proceedings of MMB 2018, Erlangen, Germany.

• A New QoE Fairness Index for QoE Management

Quality and User Experience 3:4, 2018 — Springer

• No Silver Bullet: QoE Metrics, QoE Fairness, and User Diversity in the Context of QoE Management

In proceedings of QoMEX 2017, Erfurt, Germany

• Embracing Uncertainty: A Probabilistic View of HTTP Video Quality

In IEEE/IFIP IM QoE-Management, Lisbon, Portugal.

• Definition of QoE Fairness in Shared Systems

IEEE Communications Letters, vol. 21, no. 1, pp. 184-187

• QoE beyond the MOS: an in-depth look at QoE via better metrics and their relation to MOS

Quality and User Experience 1(1):1-23, Springer.

# Recent & Upcoming Talks

### QoE Management Out of the Lab and Into the Real World (invited lecture)

QoE-NET Summer School

### Quality of Experience in OTT Video Services

Celtic-Plus NOTTS Final Seminar

### The Road to QoE Management (keynote speech)

IEEE ICC QoE-FI 2016

### Towards an Open Architecture for QoE Management

ETSI STQ Workshop

### QoE for Cloud Services (invited talk)

ITC27/ACROSS Workshop

IWCMC/TRAC 2015

### QoE-driven Management: from Modelling to Operation

Tutorial at EU CROSSFIRE doctoral workshop

# Recent Posts

### Fractals — Complexity from Simplicity — Part 2

Beyond L-Systems In the first part of this post, we went over Lindenmayer systems, and saw how from small sets of very simple rules, complexity emerged in the form of intricate patterns. In this part, we will look at two other types of fractals. The first one, is called the Barnsley fern, and unlike the L-systems in the previous post, it is based not on string substitution, but on the repeated iteration of affine transformations to a starting point.

### Fractals — Complexity from Simplicity (and a bit of Clojure)

Enter the Dragon Fractals have always fascinated me. I remember seeing a render of a Mandelbrot set back in the early 90s (when color screens started being accessible back home), and being completely mesmerized by it. I remember being even more fascinated by seeing a code-golf version of such a renderer, implemented in some 300 bytes of C. Some days ago I came across the "dragon curve", and decided to give it a go in Clojure, as a way to learn a bit more and have some fun.

### Simple Binary Data Visualization

Introduction A few days ago I ran across this discussion on Hacker News, which referred to this article on binary data visualization. The folks at Codisec have developed a tool called Veles for visualizing binary files. The idea is to help detect patterns in the data, which in some cases are useful for e.g,. security-related analysis. The technique described was surprisingly simple, in that it looks at digrams or trigrams in the file, and then it analyses their frequency and spatial distribution within the data.

# Interests

I enjoy a variety of extra-curricular activities, such as photography, cooking, and calligraphy.

Other hobbies include diving, tinkering with technology, and learning new things.