<span lang="en">This paper presents a comprehensive model intended to analyze quality of service in telecommunications services and its causes. Although many works have been published in this area, both from a technical viewpoint as well as taking into consideration subjective concerns, they have not resulted in a unique methodology to assess the experienced quality. While most of the studies consider the quality of service only from a technical and end-to-end point of view, we try to analyze quality of service as a general gauge of final users' satisfaction. The proposed model allows us to estimate the quality experienced by end users, while offering detailed results regarding the responsibility of the different agents involved in the service provision. Once we overview the most significant elements of the model, an in-depth analytical study is detailed. Finally, we illustrate a practical study for web browsing service in order to validate the theoretical model.</span>