Method and device for transmitting data unit

1. A method of transmitting, by a transmitting device, data units in a wireless communication system, the method comprising:

receiving, at a radio link control (RLC) entity of a protocol stack of the transmitting device from an upper layer of the protocol stack of the transmitting device, a first RLC service data unit (SDU);

constructing, at the RLC entity, a RLC protocol data unit (PDU) from the first RLC SDU;

based on the upper layer indicating that the RLC entity should discard the first RLC SDU, determining, at the RLC entity, whether the first RLC SDU or at least one segment of the first RLC SDU is included in an RLC PDU which has been submitted to a Medium Access Control (MAC) layer of the protocol stack of the transmitting device;

discarding, at the RLC entity, the first RLC SDU based on a determination that neither the first RLC SDU nor any segment of the first RLC SDU is included in an RLC PDU which has been submitted to the MAC layer of the protocol stack of the transmitting device; and

not discarding, at the RLC entity, the first RLC SDU based on a determination that the first RLC SDU or at least one segment of the first RLC SDU is included in an RLC PDU which has been submitted to the MAC layer of the protocol stack of the transmitting device.

2. The method according to claim 1 , wherein not discarding the first RLC SDU comprises:

based on a determination that at least one segment of the first RLC SDU is included in an RLC PDU which has been submitted to the MAC layer:

determining a remaining segment of the first RLC SDU that remains at the RLC entity; and

submitting another RLC PDU, which includes the remaining segment of the first RLC SDU, to the MAC layer.

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

based on a determination that the first RLC SDU or at least one segment of the first RLC SDU is included in the RLC PDU which has been submitted to the MAC layer of the protocol stack of the transmitting device:

transmitting, using a transceiver of the transmitting device, a data unit that comprises the RLC PDU which includes the first RLC SDU or at least one segment of the first RLC SDU.

4. The method according to claim 1 , further comprising:

based on discarding the first RLC SDU at the RLC entity:

determining a plurality of discarded RLC SDUs, including the first RLC SDU, that have been discarded at the RLC entity;

determining a plurality of remaining RLC SDUs that remain at the RLC entity;

determining a plurality of first RLC sequence numbers (SNs) associated with the plurality of discarded RLC SDUs;

determining a plurality of second RLC SNs associated with the plurality of remaining RLC SDUs; and

re-associating the plurality of remaining RLC SDUs with a plurality of third RLC SNs consecutively, starting from a lowest RLC SN among the plurality of first RLC SNs that were associated with the plurality of discarded RLC SDUs.

5. A transmitting device configured to transmit data units in a wireless communication system, the transmitting device comprising:

a transceiver;

at least one processor; and

at least one computer memory that is operably connectable to the at least one processor and that has stored thereon instructions which, when executed, cause the at least one processor to perform operations comprising:

receiving, at a radio link control (RLC) entity of a protocol stack of the transmitting device from an upper layer of the protocol stack of the transmitting device, a first RLC service data unit (SDU);

constructing, at the RLC entity, a RLC protocol data unit (PDU) from the first RLC SDU;

based on the upper layer indicating that the RLC entity should discard the first RLC SDU, determining, at the RLC entity, whether the first RLC SDU or at least one segment of the first RLC SDU is included in an RLC PDU which has been submitted to a Medium Access Control (MAC) layer of the protocol stack of the transmitting device;

discarding, at the RLC entity, the first RLC SDU based on a determination that neither the first RLC SDU nor any segment of the first RLC SDU is included in an RLC PDU which has been submitted to the MAC layer of the protocol stack of the transmitting device; and

not discarding, at the RLC entity, the first RLC SDU based on a determination that the first RLC SDU or at least one segment of the first RLC SDU is included in an RLC PDU which has been submitted to the MAC layer of the protocol stack of the transmitting device.

6. The transmitting device according to claim 5 , wherein not discarding the first RLC SDU comprises:

based on a determination that at least one segment of the first RLC SDU is included in an RLC PDU which has been submitted to the MAC layer:

determining a remaining segment of the first RLC SDU that remains at the RLC entity; and

submitting another RLC PDU, which includes the remaining segment of the first RLC SDU, to the MAC layer of the protocol stack of the transmitting device.

7. The transmitting device according to claim 5 , wherein the operations further comprises:

based on a determination that the first RLC SDU or at least one segment of the first RLC SDU is included in the RLC PDU which has been submitted to the MAC layer of the protocol stack of the transmitting device:

controlling the transceiver to transmit a data unit that comprises the RLC PDU which includes the first RLC SDU or at least one segment of the first RLC SDU.

8. The transmitting device according to claim 5 , wherein the operations further comprise:

based on discarding the first RLC SDU at the RLC entity:

determining a plurality of discarded RLC SDUs, including the first RLC SDU, that have been discarded at the RLC entity;

determining a plurality of remaining RLC SDUs that remain at the RLC entity;

determining a plurality of first RLC sequence numbers (SNs) associated with the plurality of discarded RLC SDUs;

determining a plurality of second RLC SNs associated with the plurality of remaining RLC SDUs; and

re-associating the plurality of remaining RLC SDUs with a plurality of third RLC SNs consecutively, starting from a lowest RLC SN among the plurality of first RLC SNs that were associated with the plurality of discarded RLC SDUs.

9. The method according to claim 1 , wherein the upper layer indicating that the RLC entity should discard the first RLC SDU comprises:

generating a discard indication for the first RLC SDU at the upper layer based on an expiration of a timer; and

submitting the discard indication from the upper layer to the RLC entity of the protocol stack.

10. The method according to claim 1 ,

wherein the upper layer of the protocol stack comprises a Packet Data Convergence Protocol (PDCP) layer of the protocol stack of the transmitting device.

11. The method according to claim 1 ,

wherein the transmitting device further comprises at least one computer memory that is configured to provide an RLC buffer that stores RLC SDUs, and

wherein discarding, at the RLC entity, the first RLC SDU comprises:

controlling the at least one computer memory to discard the first RLC SDU from the RLC buffer.

12. The method according to claim 4 , further comprising:

submitting, to the MAC layer of the protocol stack, the plurality of remaining RLC SDUs that have been re-associated with the plurality of third RLC SNs.

13. The transmitting device according to claim 5 , wherein the upper layer indicating that the RLC entity should discard the first RLC SDU comprises:

generating a discard indication for the first RLC SDU at the upper layer based on an expiration of a timer; and

submitting the discard indication from the upper layer to the RLC entity of the protocol stack.

14. The transmitting device according to claim 5 ,

wherein the upper layer of the protocol stack comprises a Packet Data Convergence Protocol (PDCP) layer of the protocol stack of the transmitting device.

15. The transmitting device according to claim 5 ,

wherein the at least one computer memory is further configured to provide an RLC buffer that stores RLC SDUs, and

wherein discarding, at the RLC entity, the first RLC SDU comprises:

controlling the at least one computer memory to discard the first RLC SDU from the RLC buffer.

16. The transmitting device according to claim 8 , wherein the operations further comprise:

submitting, to the MAC layer of the protocol stack, the plurality of remaining RLC SDUs that have been re-associated with the plurality of third RLC SNs.

17. The method according to claim 1 , wherein discarding the first RLC SDU at the RLC entity is performed so as not to introduce a gap in RLC sequence numbers (SNs) associated with RLC SDUs.

18. The transmitting device according to claim 5 , wherein discarding the first RLC SDU at the RLC entity is performed so as not to introduce a gap in RLC sequence numbers (SNs) associated with RLC SDUs.