For at least a decade, Quality of Service (QoS) has been one of the dominating research topics in the area of communication networks. Whereas the Internet originally has been conceived as a best-effort network, the introduction of QoS architectures like Integrated Services or Differentiated Services was supposed to pave the way for high-quality real-time services like Voice-over-IP or video streaming and thus to increase the competitiveness of packet-based TCP/IP networks.

Originally, the notion of end-to-end QoS was, according e.g. to ITU-T, aiming at the "degree of satisfaction of a user of the service". In the course of time, however, the dominating research perspective on QoS has become more and more a technical one, focussing on monitoring and improving network performance parameters like packet loss rate, delay or jitter. But end users usually are not bothered at all about technical performance; what they really care about is the experience they are able to obtain, and the Internet provided, even without any QoS mechanisms, a lot of new experiences, like web-browsing, e-mail and search engines.

Based on this insight, we have recently observed an important paradigm shift as far as service quality is concerned. While the prior “grand challenges” of QoS research have begun to disappear from the research agenda, e.g. due to large-scale overprovisioning in today’s core networks, a counter movement has started to become visible, with the aim of interpreting “end-to-end quality” in the proper sense of regarding the human being as the end of the communication chain. As a result, the notion of Quality of Experience (QoE, abbreviated also as QoX) has appeared, describing quality as perceived by the human user instead of as captured by (purely technical) network parameters.

Currently, there are several attempts to define QoE, but the ultimate definition is still lacking. According to [2], Quality of Experience may be defined as “overall acceptability of an application or service as perceived subjectively by the end-use”. Hence, Quality of Experience is a subjective measure from the user’s perspective of the overall value of the service provided, and thus does not replace, but augment end-to-end QoS by providing the quantitative link to user perception. As such, it extends the current QoS perspective described above towards the actual end user, including technical QoS as well as the expectations of the end users, the content of the service, the importance of service for the end user, the characteristics of the device, the usability of the human-computer interfaces, the joyfulness of interaction, the perception of security, and maybe even the price of the service, to name but a few new ingredients.

Today, research on Quality of Experience faces the challenge of creating a unifying interdisciplinary framework that is able to combine these diverse aspects under a common umbrella in a way that we are able to predict the behaviour of end users when new services are offered to them and to ensure service provisioning and management that actually meets user expectations. Therefore, understanding the transition from Quality of Service to Quality of Experience will become an indispensable prerequisite for taking the subjective user experience into proper account while designing and providing successful future communication services.

The Dagstuhl Seminar 09192 was an important “kick-off” to reconsider the concept of QoE, leaving more questions open than there were before the seminar, and for the formation of a community which already has taken first steps to drive the questions further. As Dagstuhl offers perfect surroundings for creative and open discussions, both community and organisers would be very much interested in a follow-up Dagstuhl Seminar.