Communication method, base station, terminal device, and system

1. A communication method, comprising:

sending, by a source base station, packet data convergence protocol (PDCP) service data units (SDUs) to a terminal device using a first bearer of a first session, wherein the first session is a session corresponding to the terminal device;

sending, by the source base station, a handover request message to a target base station, wherein the handover request message is used to instruct to hand over the first session of the terminal device from the source base station to the target base station, wherein the handover request message comprises first information, wherein the first information comprises information about at least two quality of service (QoS) flows in the first session;

receiving, by the source base station, a handover request response message from the target base station, wherein the handover request response message comprises second information, wherein the second information is used to indicate that the target base station accepts a first QoS flow in the first session, and wherein the at least two QoS flows comprises the first QoS flow;

receiving, by the source base station, third information and fourth information from the target base station, wherein the third information is used to indicate that the target base station rejects a second QoS flow in the first session, the fourth information is used to indicate a reason why the second QoS flow is rejected, and wherein the at least two QoS flows comprises the second QoS flow;

in response to receiving the handover request response message, sending, by the source base station, a radio resource control (RRC) connection reconfiguration message to the terminal device, wherein the RRC connection reconfiguration message comprises instruction information instructing the terminal device to establish a second bearer of the first session between the terminal device and the target base station;

receiving, by the source base station, sixth information from the target base station, wherein the sixth information is used to indicate a mapping relationship between the first QoS flow and the second bearer of the first session, and wherein the second bearer is a bearer between the terminal device and the target base station; and

sending, by the source base station, the sixth information to the terminal device.

2. The communication method according to claim 1 , wherein the reason why the second QoS flow is rejected comprises at least one of the following: no resource is available, QoS flow information is not supported, QoS flow information is invalid, or 5G QoS identifier (5QI) information is invalid.

3. The communication method according to claim 1 , further comprising:

sending, by the source base station, fifth information to the terminal device, wherein the fifth information is used to indicate that the target base station accepts the first QoS flow in the first session.

4. The communication method according to claim 3 , wherein the fifth information is carried in a first radio resource control (RRC) message, and wherein the first RRC message is used to instruct the terminal device to hand over from the source base station to the target base station.

5. The communication method according to claim 1 , further comprising:

sending, by the source base station, first data to the target base station, wherein the first data is data that is received by the source base station from a core network and that corresponds to the first QoS flow in the first session.

6. The communication method according to claim 5 , wherein the sending, by the source base station, first data to the target base station comprises:

sending, by the source base station, the first data to the target base station through a session tunnel.

7. A communication method, comprising:

receiving, by a terminal device, packet data convergence protocol (PDCP) service data units (SDUs) from a source base station using a first bearer of a first session, wherein the first session is a session corresponding to the terminal device;

receiving, by the terminal device, a first radio resource control (RRC) message from the source base station, wherein the first RRC message is used to instruct the terminal device to hand over from the source base station to a target base station, wherein the first RRC message comprises instruction information instructing the terminal device to establish a second bearer of the first session between the terminal device and the target base station, wherein the first RRC message comprises fifth information, wherein the fifth information is used to indicate that the target base station accepts a first quality of service (QoS) flow in the first session, wherein the source base station receives third information and fourth information from the target station, and wherein the third information is used to indicate that the target base station rejects a second QoS flow in the first session, and the fourth information is used to indicate a reason why the second QoS flow is rejected;

receiving, by the terminal device, sixth information from the source base station, wherein the sixth information is used to indicate a mapping relationship between the first QoS flow and the second bearer of the first session, and wherein the second bearer is a bearer between the terminal device and the target base station; and

sending, by the terminal device, a first RRC response message to the target base station, wherein the first RRC response message is used to respond to the first RRC message.

8. A base station, wherein the base station is a source base station, and wherein the base station comprises:

a communications interface;

a memory, configured to store instructions; and

at least one processor, connected to the memory and the communications interface, wherein the instructions, when executed by the at least one processor, instruct the at least one processor to perform the following steps:

sending packet data convergence protocol (PDCP) service data units (SDUs) to a terminal device using a first bearer of a first session, wherein the first session is a session corresponding to the terminal device;

sending a handover request message to a target base station through the communications interface, wherein the handover request message is used to instruct to hand over the first session of the terminal device from the source base station to the target base station, wherein the handover request message comprises first information, wherein the first information comprises information about at least two quality of service (QoS) flows in the first session;

receiving a handover request response message from the target base station through the communications interface, wherein the handover request response message comprises second information, wherein the second information is used to indicate that the target base station accepts a first QoS flow in the first session, and wherein the at least two QoS flows comprises the first QoS flow;

receiving third information and fourth information from the target base station, wherein the third information is used to indicate that the target base station rejects a second QoS flow in the first session, the fourth information is used to indicate a reason why the second QoS flow is rejected, and wherein the at least two QoS flows comprises the second QoS flow;

in response to receiving the handover request response message, sending a radio resource control (RRC) connection reconfiguration message to the terminal device, wherein the RRC connection reconfiguration message comprises instruction information instructing the terminal device to establish a second bearer of the first session between the terminal device and the target base station;

receiving sixth information from the target base station through the communications interface, wherein the sixth information is used to indicate a mapping relationship between the first QoS flow and the second bearer of the first session, and wherein the second bearer is a bearer between the terminal device and the target base station; and

sending the sixth information to the terminal device.

9. The base station according to claim 8 , wherein the reason why the second QoS flow is rejected comprises at least one of the following: no resource is available, QoS flow information is not supported, QoS flow information is invalid, or QoS flow information is invalid.

10. The base station according to claim 8 , wherein the instructions further instruct the at least one processor to send fifth information to the terminal device through the communications interface, wherein the fifth information is used to indicate that the target base station accepts the first QoS flow in the first session.

11. The base station according to claim 10 , wherein the fifth information is carried in a first radio resource control (RRC) message, and wherein the first RRC message is used to instruct the terminal device to hand over from the source base station to the target base station.

12. A terminal device, comprising:

a communications interface;

a memory, configured to store instructions; and

at least one processor, connected to the memory and the communications interface, wherein the instructions, when executed by the at least one processor, instruct the at least one processor to perform the following steps:

receiving packet data convergence protocol (PDCP) service data units (SDUs) from a source base station using a first bearer of a first session, wherein the first session is a session corresponding to the terminal device;

receiving a first radio resource control (RRC) message from the source base station through the communications interface, wherein the first RRC message is used to instruct the terminal device to hand over from the source base station to a target base station, wherein the first RRC message comprises instruction information instructing the terminal device to establish a second bearer of the first session between the terminal device and the target base station, wherein the first RRC message comprises fifth information, and wherein the fifth information is used to indicate that the target base station accepts a first quality of service (QoS) flow in the first session, wherein the source base station receives third information and fourth information from the target station, and wherein the third information is used to indicate that the target base station rejects a second QoS flow in the first session, and the fourth information is used to indicate a reason why the second QoS flow is rejected;

receiving sixth information from the source base station through the communications interface, wherein the sixth information is used to indicate a mapping relationship between the first QoS flow and the second bearer of the first session, and wherein the second bearer is a bearer between the terminal device and the target base station; and

sending a first RRC response message to the target base station through the communications interface, wherein the first RRC response message is used to respond to the first RRC message.