Communication Method and Communications Device

A core network device, comprising:

• a processor;
• and
• a memory coupled to the processor and configured to stored instructions executable by the processor to cause the core network device to:
• receive a first request when a user equipment roams from a first network to a second network, wherein the first request is a user authentication request or an authentication data request, wherein the second network is a 5th generation (5G) standalone network, wherein the first network is a 5G non-standalone network, and wherein the core network device is in the first network;
• generate an authentication vector quintet after receiving the first request, wherein a 0th bit of an authentication management field in the authentication vector quintet is set to 1;
• and
• send a response to the first request, wherein the response to the first request carries the authentication vector quintet.

A third core network device, comprising:

• a processor;
• and
• a memory coupled to the processor and configured to store instructions executable by the processor to cause the third core network device to:
• receive a second user authentication request from a second core network device when a user equipment roams from a first network to a second network, wherein the second network is a 5th generation (5G) standalone network, wherein the first network is a 5G non-standalone network, wherein the third core network device is in the first network or the second network, and wherein the second core network device is in the second network;
• send a first request to a first core network device in the first network, wherein the first request is a first user authentication request or a first authentication data request;
• receive a response to the first request from the first core network device, wherein the response carries an authentication vector quintet, and wherein a 0th bit of an authentication management field in the authentication vector quintet is set to 1;
• generate a 5G authentication vector for the user equipment using the authentication vector quintet;
• and
• send a user authentication response to the second core network device, wherein the user authentication response carries the 5G authentication vector.