Method and apparatus for PDCP SDU discard operation 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 for at least one Data Radio Bearer (DRB);

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

starting, by the terminal, a discard timer for a Service Data Unit (SDU) of the DRB; and

discarding, by the terminal, at least one SDU,

wherein the set of PDCP parameters comprises:

a parameter related to first discard operation; and

a parameter related to PDCP status report,

wherein, in case that the discard timer expires, the terminal performs a first discard operation,

wherein, in case that successful delivery of the SDU is confirmed by a PDCP status report, the terminal performs a second discard operation,

wherein, for the first discard operation, the terminal:

discards the SDU; and

discards one or more SDUs of a Protocol Data Unit (PDU) set,

wherein, for the second discard operation, the terminal:

discards the SDU; and

does not discard the one or more SDUs of the PDU set, and

wherein the SDU belongs to the PDU set.

2 . The method of claim 1 ,

wherein the set of PDCP parameters further comprises:

a parameter indicating length of the discard timer,

a parameter indicating uplink PDCP Sequence Number Size; and

a parameter indicating downlink PDCP Sequence Number Size.

3 . The method of claim 2 , wherein:

the terminal associates a COUNT value with the SDU when the SDU is delivered to a PDCP entity from upper layers; and

PDCP Sequence Number (SN) of the SDU is determined based on:

the COUNT value; and

the parameter related to uplink PDCP Sequence Number Size.

4 . The method of claim 1 ,

wherein the parameter related to PDCP status report indicates whether the DRB is configured to send the PDCP status report in uplink.

5 . The method of claim 1 ,

wherein the terminal starts the discard timer for a PDCP SDU when the PDCP SDU is delivered from upper layers to a PDCP entity.

6 . The method of claim 1 ,

wherein the PDU set comprises one or more data units carrying payload of one unit of information generated at an application level.

7 . The method of claim 6 ,

wherein each of the one or more data units is comprised in each of the one or more SDUs.

8 . The method of claim 1 ,

wherein the PDCP status report comprises fields indicating which SDUs are missing and which SDUs are correctly received.

9 . The method of claim 1 ,

wherein the PDCP status report is triggered in case that a specific RRC message is received.

10 . The method of claim 9 ,

wherein the specific RRC message is an RRC message instructing PDCP reestablishment.

11 . The method of claim 9 ,

wherein the specific RRC message is an RRC message instructing PDCP recovery.

12 . 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 for at least one Data Radio Bearer (DRB),

establish a DRB based on the set of PDCP parameters,

start a discard timer for a Service Data Unit (SDU) of the DRB, and

discard at least one SDU,

wherein the set of PDCP parameters comprises:

a parameter related to first discard operation; and

a parameter related to PDCP status report,

wherein, in case that the discard timer expires, the terminal performs a first discard operation,

wherein, in case that successful delivery of the SDU is confirmed by a PDCP status report, the terminal performs a second discard operation,

wherein, for the first discard operation, the terminal:

discards the SDU; and

discards one or more SDUs of a Protocol Data Unit (PDU) set,

wherein, for the second discard operation, the terminal:

discards the SDU; and

does not discard the one or more SDUs of the PDU set, and

wherein the SDU belongs to the PDU set.