According to a first exemplary embodiment a method is performed by a first network node for monitoring the QoS of a flow. A session setup message comprising a QoS configuration for the flow and an indication that the flow is subject to QoS notification control is received (1710) from a core network node. Based on the QoS configuration, radio resources to be used for the flow are determined (1720) and a resource setup message comprising an identification of the radio resources and an indication that the flow and/or the radio resources are subject to QoS notification control is sent (1730) to a second network node. A first notification control indication that the QoS configuration the flow and/or the radio resources cannot be fulfilled is received (1740) from the second network node and a resource notification message indicating that the QoS configuration for the flow cannot be fulfilled is sent (1750) to the core network node.