A controller receives an access request message of a to-be-served flow that is sent by a network device. The access request message includes an identifier of the to-be-served flow and an identifier of a terminal that sends the to-be-served flow. The controller determines service level information of the to-be-served flow based on the identifier of the terminal and the identifier of the to-be-served flow. The controller determines a transmission path of the to-be-served flow and a transmission path of a being-served flow based on the service level information of the to-be-served flow and service level information of the being-served flow. The controller publishes the transmission path of the to-be-served flow and the transmission path of the being-served flow to the network device.