In actual network deployment, each network device may be connected to multiple other node devices. For example, a serving gateway (Serving Gateway, SGW) is connected to multiple mobility management entities or connected to multiple PGWs. A process in which a terminal device accesses a network and uses a communications network to perform communication is complex. First, a process in which the terminal device accesses the network upon power-on is an attach process, and after the attach process is successfully completed, the terminal device accesses the network. Then, when the terminal device uses a network resource to perform communication, a bearer resource needs to be established, so as to implement data transmission. Then, a process of establishing a bearer needs to be performed. If quality of service (Quality of Service, QoS) of the bearer resource needs to be modified in a communication process, possibly, a process of modifying the bearer resource needs to be performed. In addition, when a user does not use the terminal device to perform communication for a long time, the terminal device may switch to an idle state, and if the user re-initiates a service, such as a voice call or Internet surfing, the terminal device initiates a service request process and switches from the idle state to a connected state. An actual communication process is quite complex and includes many processes, for example, separation process or an event reporting process such as location reporting.
In some scenarios, for example, a large quantity of users are moved on some transportation tools, a large quantity of users may simultaneously initiate an attach process; then a large quantity of create session request/response (Create Session Request/Response) messages are generated between an SGW and a PGW, or a large quantity of users simultaneously initiate a service request (Service Request) process. Correspondingly, the process triggers a large quantity of modify bearer request (Modify bearer request) messages between a mobility management entity (Mobility Management Entity, MME) and the SGW, and also triggers some signaling between the SGW and the PGW. Then, in this scenario, device overload may be caused, there may be overload of the MME, overload of the SGW, overload of the PGW, or the like. Meanwhile, a problem that device load is unbalanced may also occur; for example, some devices are heavily loaded whereas other devices are lightly loaded.