Method and apparatus for performing state variable update operation based on received PDCP control PDU in mobile wireless communication system

1 . A method by a terminal, the method comprising:

receiving, by the terminal from a base station, a Radio Resource Control (RRC) message, wherein the RRC message comprises a set of Packet Data Convergence Protocol (PDCP) parameters;

establishing, by the terminal, a PDCP entity based on the set of PDCP parameters;

receiving, by the terminal from the base station, a PDCP discard report; and

updating, by the terminal, a first state variable based on the PDCP discard report,

wherein the first state variable relates to start of a reordering timer, and

wherein one or more PDCP Service Data Units (SDUs) are delivered from the PDCP entity to an upper layer in case that the reordering timer expires.

2 . The method of claim 1 ,

wherein the terminal updates the first state variable in case that the first state variable is smaller than or equal to a highest COUNT value of PDCP SDUs that are indicated as discarded in the PDCP discard report.

3 . The method of claim 1 ,

wherein the first state variable indicates COUNT value of next PDCP SDU expected to be received.

4 . The method of claim 1 ,

wherein the first state variable is updated based on a specific PDCP SDU being received.

5 . The method of claim 4 , wherein:

the specific PDCP SDU is associated with a specific COUNT; and

the specific COUNT is greater than or equal to the first state variable.

6 . The method of claim 1 ,

wherein the reordering timer starts in case that the first state variable is greater than a second state variable.

7 . The method of claim 6 ,

wherein the second state variable indicates COUNT value of first PDCP SDU not delivered to the upper layer.

8 . The method of claim 1 ,

wherein the set of PDCP parameters further comprises:

a parameter related to uplink PDCP Sequence Number Size;

a parameter related to downlink PDCP Sequence Number Size;

a parameter related to the reordering timer; and

a parameter related to discard report.

9 . The method of claim 8 ,

wherein the terminal determines COUNT value of PDCP SDU based on the parameter related to a downlink PDCP Sequence Number Size when the PDCP SDU is delivered the PDCP entity from a lower layer.

10 . The method of claim 8 ,

wherein the parameter related to discard report indicates whether the PDCP discard report is configured to be sent.

11 . The method of claim 1 ,

wherein the PDCP discard report comprises a first field indicating at least one PDCP SDU that is discarded.

12 . The method of claim 11 ,

wherein the first field of the PDCP discard report indicates a specific COUNT.

13 . The method of claim 12 ,

wherein the specific COUNT is a lowest COUNT of SDUs that are discarded due to expiry of discard timer.

14 . The method of claim 11 ,

wherein the PDCP discard report further comprises a second field.

15 . The method of claim 14 ,

wherein the second field indicates one or more discarded SDUs other than a first discarded SDU.

16 . A terminal comprising:

a transceiver,

a memory, and

a controller coupled to the transceiver and the memory, wherein the controller is configured to cause the terminal to:

receive, from a base station, a Radio Resource Control (RRC) message, wherein the RRC message comprises a set of Packet Data Convergence Protocol (PDCP) parameters,

establish a PDCP entity based on the set of PDCP parameters,

receive, from the base station, a PDCP discard report, and

update a first state variable based on the PDCP discard report,

wherein the first state variable relates to start of a reordering timer, and

wherein one or more PDCP Service Data Units (SDUs) are delivered from the PDCP entity to an upper layer in case that the reordering timer expires.