This application provides an information transmission method when a terminal device accesses a serving radio access network (RAN) device. The terminal device receives an identifier of a first cluster-data function (C-DF) associated with the serving RAN device from the serving RAN device, where the first C-DF is located in a radio access network and stores current data of the terminal device. When the terminal device camps on the serving RAN device longer than or equal to a first threshold, the terminal device stores the identifier of the first C-DF.