This application provides a data transmission method, a communications apparatus, and a session management function entity. The method includes obtaining, by a communications apparatus, a correspondence between a quality of service flow identifier of a service flow and an inter-packet time interval of the service flow. The method also includes establishing, by the communications apparatus based on the correspondence, a gate queue used to send a data packet. The method further includes establishing a mapping relationship between the gate queue and the quality of service flow identifier. The method also includes receiving, by the communications apparatus, a data packet from an upper-level sending device of a transmission link. The method further includes if the data packet includes the quality of service flow identifier, periodically scheduling, by the communications apparatus, the data packet based on the gate queue to which the quality of service flow identifier is mapped.