Indirect registration method and apparatus

A communication system, comprising:

• a first access and mobility management function network element located in a first network;
• and a second access and mobility management function network element located in a second network;
• wherein
• the first access and mobility management function network element is configured to receive a first message from a terminal device, wherein the first message comprises first identification information of the terminal device, the first identification information is identification information of the terminal device in a first network, and the first message is used request registration of the terminal device with the first network;
• obtain second identification information of the terminal device based on the first identification information, wherein the second identification information is identification information of the terminal device in the second network;
• and
• send a second message to the second access and mobility management function network element, wherein the second message comprises the second identification information, and the second message is used to request registration of the terminal device with the second network;
• and
• the second access and mobility management function network element is configured to receive the second message, and register the terminal device with the second network based on the second identification information.

A communications apparatus located in a first network, the communications apparatus comprising a processor and a memory;

• the memory configured to store a program, and
• the processor configured to invoke the program stored in the memory, to perform a method comprising:
• receiving a first message from a terminal device, wherein the first message is used to request registration of the terminal device with the first network, wherein the first message comprises first identification information of the terminal device, and the first identification information is identification information of the terminal device in the first network;
• obtaining second identification information of the terminal device based on the first identification information, wherein the second identification information is identification information of the terminal device in a second network;
• and
• sending a second message to a second access and mobility management function network element, wherein the second message is used to request registration of the terminal device with the second network, the second message comprises the second identification information, and the second access and mobility management function network element is located in the second network.