With increase of user terminals (UE, User Equipment), an existing radio communications system cannot meet radio communication requirements of a user. Therefore, it is urgent to increase a system capacity of the radio communications system. The system capacity can be increased by adding a base station. A typical practice is to densely deploy many small cells in a macro cell to form more pico cells. However, most UEs are connected to only one base station, and this base station provides a radio communications service for the UE. For ease of description, the base station that provides the radio communications service for the UE is referred to as a serving node of the UE.
In the prior art, when the UE moves from one cell to another cell or when the UE moves from a coverage area of one base station to a coverage area of another base station or when the UE discovers a radio link failure (RLF, Radio Link Failure), the UE may switch the serving node. That is, the serving node of the UE changes from one base station to another base station. Because the serving node is connected to a mobility management entity (MME, Mobility Management Entity) through a control plane interface, and the serving node is connected to an SGW (Serving Gateway, serving gateway) through a user plane interface, after the serving node of the UE is changed, signaling needs to be sent between a new serving node and the MME to update an S1 control plane connection between the serving node and the MME; at the same time, signaling also needs to be sent between the MME and the SGW to update an S1 user plane connection between the serving node and the SGW. In this way, each handover process brings at least four messages. When density of deployed base stations increases, handover increases sharply, and causes signaling load of a core network to increase sharply. In addition, each serving node is connected to the MME through a control plane interface. When the MME needs to send a paging message, the MME sends the paging message to all base stations in a TA (tracking area, tracking area) corresponding to the paging message, and this causes the signaling load of the core network to increase sharply.