Method for handling data lossless in a UM RLC entity in wireless communication system and a device therefor

1. A method for a transmitting device operating in a wireless communication system, the method comprising:

receiving a Radio Resource Control (RRC) message for releasing or reestablishing of a Unacknowledged Mode (UM) Radio Link Control (RLC) entity;

transmitting, by the UM RLC entity to a Packet Data Convergence Protocol (PDCP) entity associated with the UM RLC entity, information for transmission status of RLC Service Data Units (SDUs) stored in the UM RLC entity; and

discarding all RLC SDUs and Unacknowledged Mode Data (UMD) Protocol Data Units (PDUs) stored in the UM RLC entity,

wherein the UM RLC entity is released when the RRC message includes information for the release of the UM RLC entity, and

wherein the UM RLC entity is re-established when the RRC message includes information for the re-establishment of the UM RLC entity.

2. The method according to claim 1 , wherein when a bearer type for the UM RLC entity is changed from a split bearer to non-split bearer, the UM RLC entity is released.

3. The method according to claim 1 , wherein the information for transmission status of RLC SDUs includes one of following:

information whether a RLC SDU has been transmitted or not for each RLC SDU stored in the UM RLC entity, or

information of RLC SDUs not transmitted yet, or

information of RLC SDUs already transmitted.

4. The method according to claim 3 , wherein a RLC SDU whose transmission status is indicated as transmitted by the UM RLC entity is:

a RLC SDU of which any byte is submitted to a lower layer,

a RLC SDU of which all bytes are submitted to a lower layer,

a RLC SDU of which any byte is mapped to a RLC PDU, or

a RLC SDU of which all bytes are mapped to one or more RLC PDUs.

5. The method according to claim 3 , wherein a RLC SDU whose transmission status is indicated as not transmitted by the UM RLC entity is:

a RLC SDU of which any byte is not submitted to a lower layer,

a RLC SDU of which all bytes are not submitted to a lower layer,

a RLC SDU of which any byte is not mapped to a RLC PDU, or

a RLC SDU of which all bytes are not mapped to one or more RLC PDUs.

6. The method according to claim 5 , wherein if the PDCP entity is associated with another RLC entity than the released UM RLC entity, the PDCP entity retransmits RLC SDUs whose transmission status is indicated as not transmitted by the released UM RLC entity to the another RLC entity.

7. The method according to claim 5 , wherein if the PDCP entity is associated with the reestablished UM RLC entity, the PDCP entity retransmits RLC SDUs whose transmission status is indicated as not transmitted by the reestablished UM RLC entity to the reestablished UM RLC entity.

8. A transmitting device for operating in a wireless communication system, the transmitting device comprising:

a transmitter and a receiver; and

a processor operably coupled with the transmitter and the receiver and configured to:

receive a Radio Resource Control (RRC) message for releasing or reestablishing of a Unacknowledged Mode (UM) Radio Link Control (RLC) entity;

transmit, by the UM RLC entity to a Packet Data Convergence Protocol (PDCP) entity associated with the UM RLC entity, information for transmission status of RLC Service Data Units (SDUs) stored in the UM RLC entity; and

discard all RLC SDUs and Unacknowledged Mode Data (UMD) Protocol Data Units (PDUs) stored in the UM RLC entity,

wherein the UM RLC entity is released when the RRC message includes information for the release of the UM RLC entity,

wherein the UM RLC entity is re-established when the RRC message includes information for the re-establishment of the UM RLC entity.

9. The transmitting device according to claim 8 , wherein when a bearer type for the UM RLC entity is changed from a split bearer to non-split bearer, the UM RLC entity is released.

10. The transmitting device according to claim 8 , wherein the information for transmission status of RLC SDUs includes one of following:

information whether a RLC SDU has been transmitted or not for each RLC SDU stored in the UM RLC entity, or

information of RLC SDUs not transmitted yet, or

information of RLC SDUs already transmitted.

11. The transmitting device according to claim 10 , wherein a RLC SDU whose transmission status is indicated as transmitted by the UM RLC entity is:

a RLC SDU of which any byte is submitted to a lower layer,

a RLC SDU of which all bytes are submitted to a lower layer,

a RLC SDU of which any byte is mapped to a RLC PDU, or

a RLC SDU of which all bytes are mapped to one or more RLC PDUs.

12. The transmitting device according to claim 10 , wherein a RLC SDU whose transmission status is indicated as not transmitted by the UM RLC entity is:

a RLC SDU of which any byte is not submitted to a lower layer,

a RLC SDU of which all bytes are not submitted to a lower layer,

a RLC SDU of which any byte is not mapped to a RLC PDU, or

a RLC SDU of which all bytes are not mapped to one or more RLC PDUs.

13. The transmitting device according to claim 12 , wherein if the PDCP entity is associated with another RLC entity than the released UM RLC entity, the PDCP entity retransmits RLC SDUs whose transmission status is indicated as not transmitted by the released UM RLC entity to the another RLC entity.

14. The transmitting device according to claim 12 , wherein if the PDCP entity is associated with the reestablished UM RLC entity, the PDCP entity retransmits RLC SDUs whose transmission status is indicated as not transmitted by the reestablished UM RLC entity to the reestablished UM RLC entity.

15. The method according to claim 1 , wherein the transmitting device is capable of communicating with at least one of another device, a device related to an autonomous driving vehicle, a base station and/or a network.

16. The transmitting device according to claim 8 , wherein the transmitting device is capable of communicating with at least one of another device, a device related to an autonomous driving vehicle, a base station and/or a network.