Data transmission method and communication apparatus

1 . A data transmission method at a terminal device, wherein the method comprises:

receiving first information from a first access network device, wherein the first information indicates the terminal device to be handed over and connected to a second access network device; and

sending a first data packet to the second access network device after the terminal device successfully accesses the second access network device, wherein the first data packet is a data packet that has been sent by the terminal device to the first access network device before the terminal device successfully accesses the second access network device, and the first data packet is carried on a first data radio bearer (DRB) of unacknowledged mode (UM) radio link control (RLC).

2 . The method according to claim 1 , wherein the method further comprises:

configuring, based on the first information, the terminal device to transmit the first data packet to the second access network device.

3 . The method according to claim 1 , wherein the method further comprises:

receiving second information from the first access network device, wherein the second information indicates a serial number of the first data packet or a start serial number of the first data packet.

4 . The method according to claim 1 , wherein the method further comprises:

in response to the terminal device not receiving, from the first access network device, second information that indicates a serial number of the first data packet or a start serial number of the first data packet,

determining the first data packet as a data packet that is on the first DRB and that is buffered by the terminal device.

5 . The method according to claim 1 , wherein

the first information further indicates that the second access network device determines to use the first DRB, among a plurality of first DRBs, for dual active protocol stack (DAPS) handover, and

the method further comprises:

determining, from the plurality of first DRBs and based on configuration information of a logical channel associated with each of the plurality of first DRBs, at least one second DRB to carry the first data packet.

6 . The method according to claim 5 , wherein the configuration information of the logical channel comprises at least one of:

a logical channel priority configuration,

a physical layer priority index of the logical channel, or

a duration threshold of an uplink data channel corresponding to the logical channel.

7 . The method according to claim 1 , wherein the method further comprises:

configuring, based on the first information, the terminal device to send the first data packet and a second data packet to the first access network device after the terminal device successfully accesses the second access network device, wherein the second data packet is a data packet that has not been sent by the terminal device to the first access network device before the terminal device successfully accesses the second access network device.

8 . A data transmission method, wherein the method comprises:

sending, by a first access network device, a handover request message to a second access network device, wherein the handover request message carries an identifier of a terminal device;

receiving, by the first access network device and from the second access network device, a handover acknowledgment message to configure the terminal device to transmit a first data packet to the second access network device, wherein

the first data packet is a data packet that has been sent by the terminal device to the first access network device before the terminal device successfully accesses the second access network device, and

the first data packet is carried on a first data radio bearer (DRB) of unacknowledged mode (UM) radio link control (RLC); and

sending, by the first access network device, first information to the terminal device, wherein the first information indicates the terminal device to be handed over and connected to the second access network device, and the first information comprises the handover acknowledgment message.

9 . The method according to claim 8 , wherein the method further comprises:

sending, by the first access network device, second information to the terminal device, wherein the second information indicates a serial number of the first data packet or a start serial number of the first data packet.

10 . The method according to claim 8 , wherein the first information is further used to configure the terminal device to send the first data packet and a second data packet to the first access network device after the terminal device successfully accesses the second access network device, and the second data packet is a data packet that has not been sent by the terminal device to the first access network device before the terminal device successfully accesses the second access network device.

11 . A data transmission apparatus, wherein the apparatus comprises:

at least one processor; and

a memory coupled to the at least one processor and configured to store executable instructions for execution by the at least one processor to instruct the at least one processor to:

receive first information from a first access network device, wherein the first information indicates the apparatus to be handed over and connected to a second access network device; and

send a first data packet to the second access network device after the apparatus successfully accesses the second access network device, wherein the first data packet is a data packet that has been sent by the apparatus to the first access network device before the apparatus successfully accesses the second access network device, and the first data packet is carried on a first data radio bearer (DRB) of unacknowledged mode (UM) radio link control (RLC).

12 . The apparatus according to claim 11 , wherein the executable instructions further instruct the at least one processor to:

configure, based on the first information, the apparatus to transmit the first data packet to the second access network device.

13 . The apparatus according to claim 11 , wherein the executable instructions further instruct the at least one processor to:

receive second information from the first access network device, wherein the second information indicates a serial number of the first data packet or a start serial number of the first data packet.

14 . The apparatus according to claim 11 , wherein the executable instructions further instruct the at least one processor to:

in response to the apparatus not receiving, from the first access network device, second information that indicates a serial number of the first data packet or a start serial number of the first data packet,

determine the first data packet as a data packet that is on the first DRB and that is buffered by the apparatus.

15 . The apparatus according to claim 11 , wherein

the first information further indicates that the second access network device determines to use the first DRB, among a plurality of first DRBs, for dual active protocol stack (DAPS) handover, and

the executable instructions further instruct the at least one processor to:

determine, from the plurality of first DRBs and based on configuration information of a logical channel associated with each of the plurality of first DRBs, at least one second DRB to carry the first data packet.

16 . The apparatus according to claim 15 , wherein the configuration information of the logical channel comprises at least one of:

a logical channel priority configuration,

a physical layer priority index of the logical channel, or

a duration threshold of an uplink data channel corresponding to the logical channel.

17 . The apparatus according to claim 11 , wherein the executable instructions further instruct the at least one processor to:

configure, based on the first information, the apparatus to send the first data packet and a second data packet to the first access network device after the apparatus successfully accesses the second access network device, wherein the second data packet is a data packet that has not been sent by the apparatus to the first access network device before the apparatus successfully accesses the second access network device.

18 . A data transmission apparatus, wherein the apparatus comprises:

at least one processor; and

a memory coupled to the at least one processor and configured to store executable instructions for execution by the at least one processor to instruct the at least one processor to:

send a handover request message to a second access network device, wherein the handover request message carries an identifier of a terminal device;

receive, from the second access network device, a handover acknowledgment message to configure the terminal device to transmit a first data packet to the second access network device, wherein

the first data packet is a data packet that has been sent by the terminal device to the apparatus before the terminal device successfully accesses the second access network device, and

the first data packet is carried on a first data radio bearer (DRB) of unacknowledged mode (UM) radio link control (RLC); and

send first information to the terminal device, wherein the first information indicates the terminal device to be handed over and connected to the second access network device, and the first information comprises the handover acknowledgment message.

19 . The apparatus according to claim 18 , wherein the executable instructions further instruct the at least one processor to:

send second information to the terminal device, wherein the second information indicates a serial number of the first data packet or a start serial number of the first data packet.

20 . The apparatus according to claim 18 , wherein the first information is further used to configure the terminal device to send the first data packet and a second data packet to the apparatus after the terminal device successfully accesses the second access network device, and the second data packet is a data packet that has not been sent by the terminal device to the apparatus before the terminal device successfully accesses the second access network device.