Communications Method, Apparatus, and System

A communications apparatus, comprising a transceiver, a memory, and a processor, wherein the transceiver is used by the apparatus to perform communication;

• the memory is configured to store a computer program;
• and the processor is configured to invoke the computer program from the memory and run the computer program to:
• obtain information about the source session management device;
• send a first message to the source session management device based on the information, wherein the first message is for establishing a forwarding tunnel between a source intermediate user plane device and a target intermediate user plane device, wherein the source intermediate user plane device is controlled by the source session management device and is communicatively connected to a source base station, and wherein the target intermediate user plane device is controlled by the target intermediate session management device and is communicatively connected to a target base station;
• obtain information about the anchor session management device;
• and
• send downlink tunnel information of the target intermediate user plane device to the anchor session management device based on the information about the anchor session management device, wherein the downlink tunnel information is for establishing a downlink tunnel between an anchor user plane device and the target intermediate user plane device.

A communications apparatus, comprising a transceiver, a memory, and a processor, wherein the transceiver is used by the apparatus to perform communication;

• the memory is configured to store a computer program;
• and the processor is configured to invoke the computer program from the memory and run the computer program to:
• receive a first message from a target intermediate session management device, wherein the first message is for establishing a forwarding tunnel between a source intermediate user plane device and a target intermediate user plane device, wherein the source intermediate user plane device is controlled by the source session management device and is communicatively connected to a source base station, and wherein the target intermediate user plane device is controlled by the target intermediate session management device and is communicatively connected to a target base station;
• instruct based on the first message, the source intermediate user plane device to establish the forwarding tunnel;
• send information about an anchor session management device to the target intermediate session management device, wherein the information about the anchor session management device is for establishment of a downlink tunnel between an anchor user plane device and the target intermediate user plane device, wherein the anchor user plane device is controlled by the anchor session management device.