The present invention describes a method, system and network node for controlling quality of service for existing data connections using shared radio resources in a wireless communication network. The Quality Control monitors the satisfaction level of every user as well as the user satisfaction rate in the system. The purpose of this function is to indicate the degraded situation to the Admission Control. In that way, appropriate actions to counteract those situations in which the provision of QoS is not in line with the negotiated QoS for a determined amount of users can be triggered. The Quality Control indicates the Admission Control about the convenience of starting to block users that request guaranteed QoS, such as streaming service users, or non Real Time (nRT) users to avoid the degradation in the provision of QoS for those users already admitted to the system.