The present invention is applicable to access networks across which virtual connections have been provisioned to meet traffic and QoS requirements. The present invention improves service integrity by controlling the right for a service instance to use the network resources that have been provisioned for its class of service. Whenever a subscriber requests a service that requires a pre-determined bandwidth with a pre-determined QoS, one checks whether the virtual connection over which the service will be delivered to the subscriber can convey the required bandwidth with the required QoS. According to the check outcome, the service is granted or denied to the subscriber. The present invention may further improve the usage of the network resources. This second object is achieved by adapting the configuration of the access network according to the real traffic demand.