Method for reconfiguring a PDCP reordering timer in a wireless communication system and device therefor

1. A method for a User Equipment (UE) operating in a wireless communication system, the method comprising:

starting a PDCP (Packet Data Convergence Protocol) reordering timer;

receiving an RRC (Radio Resource Control) message indicating that a new value is used for the PDCP reordering timer;

re-starting the PDCP reordering timer with the new value; and

setting a reordering_PDCP_RX_COUNT to a COUNT value associated to RX_HFN and Next_PDCP_RX_SN upon when the PDCP reordering timer with the new value re-starts.

2. The method according to claim 1 , wherein the reordering_PDCP_RX_COUNT is used only when a PDCP reordering function is used, and

a value of the reordering_PDCP_RX_COUNT is a value of a COUNT following a COUNT value associated with a PDCP PDU (Protocol Data Unit) which triggered a PDCP reordering timer.

3. The method according to claim 1 , wherein a variable of the RX_HFN indicates a HFN (Hyper Frame Number) value for generation of a COUNT value used for a received PDCP PDUs for a PDCP entity.

4. The method according to claim 1 , wherein a variable of the Next_PDCP_RX_SN indicates a next expected PDCP SN (Sequence Number) by a receiver for a PDCP entity.

5. The method according to claim 1 , wherein the setting the reordering_PDCP_RX_COUNT to the COUNT value associated to RX_HFN and Next_PDCP_RX_SN corresponds to re-starting the PDCP reordering timer with new value for a PDCP SDU (Service Data Unit) with a highest COUNT value among PDCP SDUs stored in a reordering buffer.

6. The method according to claim 1 , when the RRC is received, while the PDCP reordering timer is running, the running PDCP reordering timer is stopped.

7. A User Equipment (UE) operating in a wireless communication system, the UE comprising:

a Radio Frequency (RF) unit; and

a processor configured to control the RF unit,

wherein the processor is configured to start a PDCP (Packet Data Convergence Protocol) reordering timer, to receive an RRC (Radio Resource Control) message indicating that a new value is used for the PDCP reordering timer, to re-start the PDCP reordering timer with the new value, and to set a reordering_PDCP_RX_COUNT to a COUNT value associated to RX_HFN and Next_PDCP_RX_SN upon when the PDCP reordering timer with the new value re-starts.

8. The UE according to claim 7 , wherein the reordering_PDCP_RX_COUNT is used only when a PDCP reordering function is used, and

a value of the reordering_PDCP_RX_COUNT is a value of a COUNT following a COUNT value associated with a PDCP PDU (Protocol Data Unit) which triggered a PDCP reordering timer.

9. The UE according to claim 7 , wherein a variable of the RX_HFN indicates a HFN (Hyper Frame Number) value for generation of a COUNT value used for a received PDCP PDUs for a PDCP entity.

10. The UE according to claim 7 , wherein a variable of the Next_PDCP_RX_SN indicates a next expected PDCP SN (Sequence Number) by a receiver for a PDCP entity.

11. The UE according to claim 7 , wherein the setting the reordering_PDCP_RX_COUNT to the COUNT value associated to RX_HFN and Next_PDCP_RX_SN corresponds to re-starting the PDCP reordering timer with new value for a PDCP SDU (Service Data Unit) with a highest COUNT value among PDCP SDUs stored in a reordering buffer.

12. The UE according to claim 7 , when the RRC is received, while the PDCP reordering timer is running, the running PDCP reordering timer is stopped.