<span lang="en">In last years there have been some governmental initiatives aimed at the regulation of quality of service evaluation in telecommunications services. However this has proven to be a complex task especially for Internet services, where it is difficult to objectively assess the quality of a service and to identify whether one or more of the provider agents are responsible of final dissatisfaction of users. This paper affords the cited problem and intends to provide a methodology to asses the quality of service as perceived by end users. The aims of the proposed model are twofold: the evaluation of perceived quality of service (PQoS) based on subjective and objective measurements and the identification of responsibilities of the different agents involved in a service provision.</span>