ed procedure, and taking into account all important influenc- ing factors. The output of the QoE assessment may result in a scalar value, various multi-dimensional representations of the results, as well as verbal descriptors (e.g. good, bad). In theory, all assessments of QoE should be accompanied by the descrip- tion of the influencing factors that are included. 1 Introduction Overall, the QoE includes complete end-to-end system effects (end-user equipment and application, various influencing factors on the user for the given services, as well as network and service infrastructure). So, the QoE may be influenced by user expectations and the context (e.g. for the same obtained bitrate for a given service, a user who had lower expectations will enjoy higher QoE than a user who had higher expectations for the same service on the same equipment offered via the same network). QoE takes into consideration certain additional parameters, such as: user expectations; user context (what is in trend, user's personal mood, environment where the service is being used such as work/home/outside environments, etc.); the potential difference between the service being offered to the user and the individ- ual user awareness about the service and additional features (if any) for that service. Regarding the QoE assessment, the most used measure is the mean opinion score (MOS). Initially, the MOS scale referred to voice service only (ITU-T P.800), but nowa- days it is also used for other services such as video (e.g. for IPTV). MOS is expressed as a single number in the range between 1 and 5, where MOS with a value of 1 denotes the worst and a value of 5 denotes the best quality experienced by the user (Table 1.1). 1.3.3 Network Performance (NP) Network performance differs from QoS because it relates only to the network part of the service provisioning, without taking into account different user influencing factors. On one side, the QoS is the outcome of the user's experience of using a given service and the user's perception of it, w