Packet data convergence protocol service data unit discard method and user equipment

1 . A PDCP (Packet Data Convergence Protocol) Service Data Unit (SDU) discard method, adapted for a user equipment(UE), comprising:

setting one or more discard timers based on a Radio Resource Control(RRC) configuration transmitted from a network device;

receiving a PDCP SDU from a upper layer, wherein the PDCP SDU corresponding to a PDU belonging to a PDU Set; receiving, by MAC CE, a bitmap of a PSI-based PDCP SDU discard indication from the network device, wherein the bitmap of the PSI-based PDCP SDU discard indication is to indicate whether PSI-based SDU discard operation for each of a plurality of Data Radio Bearers (DRBs) is activated or deactivated;

prior to determining whether to discard the PDCP SDU, determining, based on the bitmap, whether the PSI-based SDU discard operation for a DRB corresponding to the PDCP SDU is activated;

in response to receiving a PDU Set Importance (PSI)-based SDU discard indication from the network device and in response to the bitmap indicating that the PSI-based SDU discard operation for the DRB corresponding to the PDCP SDU is activated, determining whether to discard the PDCP SDU or not according to a PSI of the PDU Set and a target discard timer, comprising:

identifying the PSI of the PDU Set, wherein the PSI of the PDU Set indicates a relative importance of the PDU Set compared to other PDU Sets;

determining the target discard timer corresponding to the PSI among the one or more discard timers; and

discarding the PDCP SDU when the target discard timer is expired.

2 . The PDCP SDU discard method according to claim 1 , wherein the target discard timer is determined according to the PSI, and the step of determining the target discard timer corresponding to the PSI among the one or more discard timers comprises:

when the PSI is identified as high importance, selecting the target discard timer of which a duration is configured as an enumerated no-expiration timer value of a discardTimer parameter configured by the RRC configuration; and

when the PSI is identified as low importance, selecting the target discard timer of which a duration is configured as a default value, wherein the default value is indicated by the RRC configuration,

wherein the target discard timer is started when receiving the PDCP SDU.

3 . The PDCP SDU discard method according to claim 1 , wherein the target discard timer is determined according to the PSI, and the step of determining the target discard timer corresponding to the PSI among the one or more discard timers comprises:

when the PSI is identified as high importance, selecting the target discard timer of which a duration is configured as a first value according to a default value and a discard-Timer-Offset indicated by the RRC configuration; and

when the PSI is identified as low importance, selecting the target discard timer of which a duration is configured as a second value according to the default value indicated by the RRC configuration, wherein the second value is less than the first value,

wherein the target discard timer is started when receiving the PDCP SDU.

4 . The PDCP SDU discard method according to claim 1 , wherein the PSI comprises a plurality of PSI levels, the target discard timer is determined according to the PSI, and the step of determining the target discard timer corresponding to the PSI among the one or more discard timers comprises:

selecting the target discard timer of which a duration is configured by:

setting a discard-Timer-Offset based on an identified PSI level of the PSI; and

setting the duration of the target discard timer corresponding to the PSI as a sum of the discard-Timer-Offset and a default value, wherein the default value and the discard-Timer-Offset are indicated by the RRC configuration,

wherein the target discard timer is started when receiving the PDCP SDU.

5 . The PDCP SDU discard method according to claim 1 , wherein when the target discard timer of the PDCP SDU expires, the method further comprises:

determining whether PDU Set Integrated Handling Indication(PSIHI) corresponding to the PDU Set is set or not;

in response to determining that the PSIHI is set, discarding the PDCP SDU and remaining one or more PDCP SDUs of the PDU Set to which the PDCP SDU belongs; and

in response to determining that the PSIHI is not set, discarding the PDCP SDU.

6 . The PDCP SDU discard method according to claim 1 , wherein the target discard timer is determined according to the PSI, and the step of determining the target discard timer corresponding to the PSI among the one or more discard timers comprises:

when the PSI is identified as high importance, selecting the target discard timer of which a duration is configured as a first value according to a default value and a discard-Timer-Offset indicated by the RRC configuration and a time interval between receiving the PDCP SDU and receiving first one PDCP SDU of the PDU Set; and

when the PSI is identified as low importance, selecting the target discard timer of which a duration is configured as a second value according to the default value indicated by the RRC configuration and the time interval between receiving the PDCP SDU and receiving first one PDCP SDU of the PDU Set, wherein the second value is less than the first value,

wherein the target discard timer is started when receiving the PDCP SDU.

7 . The PDCP SDU discard method according to claim 1 , wherein the RRC configuration comprises a logical parameter, configured to indicate whether a PSI-based SDU discard operation for a Data Radio Bearer (DRB) is activated.

8 . The PDCP SDU discard method according to claim 1 , wherein the network device sends a PSI-based SDU discard indication to the UE, wherein the PSI-based SDU discard indication is configured to indicate whether a PSI-based PDCP SDU discard operation for the PDCP SDU is activated.

9 . The PDCP SDU discard method according to claim 1 , further comprising:

in response to determining that a further target discard timer corresponding to the PDCP SDU is expired and not receiving the PSI-based SDU discard indication from the network device, discarding the PDCP SDU when the target discard timer corresponding to the PDCP SDU is expired, wherein the corresponding discard timer is started when receiving the PDCP SDU.

10 . A user equipment (UE), comprising:

a transceiver, used for transmitting or receiving signals;

a memory, used for storing a program code; and

a processor, coupled to the transceiver and the memory, and configured for executing the program code to:

set one or more discard timers based on a Radio Resource Control(RRC) configuration transmitted from a network device;

receive a PDCP SDU (Service Data Unit) from a upper layer, wherein the PDCP SDU corresponding to a PDU belonging to a PDU Set; receive, by MAC CE, a bitmap of a PSI-based PDCP SDU discard indication from the network device, wherein the bitmap of the PSI-based PDCP SDU discard indication is to indicate whether PSI-based SDU discard operation for each of a plurality of Data Radio Bearers (DRBs) is activated or deactivated;

prior to determining whether to discard the PDCP SDU, determine, based on the bitmap, whether the PSI-based SDU discard operation for a DRB corresponding to the PDCP SDU is activated; and

in response to receiving a PSI-based SDU discard indication from the network device and in response to the bitmap indicating that the PSI-based SDU discard operation for the DRB corresponding to the PDCP SDU is activated, determine whether to discard the PDCP SDU or not according to a PSI of the PDU Set and a target discard timer, comprising:

identifying the PSI of the PDU Set, wherein the PSI of the PDU Set indicates a relative importance of the PDU Set compared to other PDU Sets;

determining the target discard timer corresponding to the PSI among the one or more discard timers; and

discarding the PDCP SDU when the target discard timer is expired.

11 . The UE according to claim 10 , wherein the target discard timer is determined according to the PSI, and the step of determining the target discard timer corresponding to the PSI among the one or more discard timers comprises:

when the PSI is identified as high importance, selecting the target discard timer of which a duration is configured as an enumerated no-expiration timer value of a discardTimer parameter configured by the RRC configuration; and

when the PSI is identified as low importance, selecting the target discard timer of which a duration is configured as a default value, wherein the default value is indicated by the RRC configuration,

wherein the target discard timer is started when receiving the PDCP SDU.

12 . The UE according to claim 10 , wherein the target discard timer is determined according to the PSI, and the step of determining the target discard timer corresponding to the PSI among the one or more discard timers comprises:

when the PSI is identified as high importance, selecting the target discard timer of which a duration is configured as a first value according to a default value and a discard-Timer-Offset indicated by the RRC configuration; and

when the PSI is identified as low importance, selecting the target discard timer of which a duration is configured as a second value according to the default value indicated by the RRC configuration, wherein the second value is less than the first value,

wherein the target discard timer is started when receiving the PDCP SDU.

13 . The UE according to claim 10 , wherein the PSI comprises a plurality of PSI levels, the target discard timer is determined according to the PSI, and the step of determining the target discard timer corresponding to the PSI among the one or more discard timers comprises:

selecting the target discard timer of which a duration is configured by:

setting a discard-Timer-Offset based on an identified PSI level of the PSI; and

setting the duration of the target discard timer corresponding to the PSI as a sum of the discard-Timer-Offset and a default value, wherein the default value and the discard-Timer-Offset are indicated by the RRC configuration,

wherein the target discard timer is started when receiving the PDCP SDU.

14 . The UE according to claim 10 , wherein when the target discard timer of the PDCP SDU expires, the processor is further configured to:

determine whether PDU Set Integrated Handling Indication (PSIHI) corresponding to the PDU Set is set or not;

in response to determining that the PSIHI is set, discard the PDCP SDU and remaining one or more PDCP SDUs of the PDU Set to which the PDCP SDU belongs; and

in response to determining that the PSIHI is not set, discard the PDCP SDU.

15 . The UE according to claim 10 , wherein the target discard timer is determined according to the PSI, and the step of determining the target discard timer corresponding to the PSI among the one or more discard timers comprises:

when the PSI is identified as high importance, selecting the target discard timer of which a duration is configured as a first value according to a default value and a discard-Timer-Offset indicated by the RRC configuration and a time interval between receiving the PDCP SDU and receiving first one PDCP SDU of the PDU Set; and

when the PSI is identified as low importance, selecting the target discard timer of which a duration is configured as a second value according to the default value indicated by the RRC configuration and the time interval between receiving the PDCP SDU and receiving first one PDCP SDU of the PDU Set, wherein the second value is less than the first value,

wherein the target discard timer is started when receiving the PDCP SDU.

16 . The UE according to claim 10 , wherein the RRC configuration comprises a logical parameter, configured to indicate whether a PSI-based SDU discard operation for a Data Radio Bearer (DRB) is activated.

17 . The UE according to claim 10 , wherein the network device sends a PSI-based SDU discard indication to the UE, wherein the PSI-based SDU discard indication is configured to indicate whether the PSI-based SDU discard operation for the PDCP SDU is activated.

18 . The UE according to claim 10 , further comprising:

in response to determining that a further target discard timer corresponding to the PDCP SDU is expired and not receiving the PSI-based SDU discard indication from the network device, discarding the PDCP SDU when the target discard timer corresponding to the PDCP SDU is expired, wherein the corresponding discard timer is started when receiving the PDCP SDU.