Method and device for processing downlink SRB message in MCG RLF
The present disclosure relates to a communication technique for converging IoT technology with a 5G communication system for supporting a higher data transmission rate beyond a 4G system, and a system therefor. The present disclosure may be applied to an intelligent service (for example, a smart home, a smart building, a smart city, a smart car or connected car, health care, digital education, retail business a security and safety-related service, etc.) on the basis of 5G communication technology and IoT-related technology. The present invention relates to a method and a device for processing a message in a cell group radio link failure situation.
1. A method by a user equipment (UE) in a wireless communication system, the method comprising:
detecting a radio link failure of a master cell group (MCG);
transmitting information on the radio link failure via a secondary cell group (SCG);
receiving data, after a transmission of the radio link failure;
in case that the data is received via a split signaling radio bearer (SRB) between the MCG and the SCG, resetting and starting a reordering timer for the split SRB based on a COUNT value of the data, wherein the reordering timer is used for detecting loss of packet data convergence protocol (PDCP) protocol data unit (PDU); and
delivering, from a PDCP entity to an upper layer, a PDCP service data unit (SDU) associated with the data based on an expiration of the reordering timer,
wherein a value of the reordering timer for the split SRB is reset from infinity to a predetermined value.
2. The method of claim 1 , wherein the predetermined time is 0.
3. The method of claim 1 ,
further comprising:
identifying a first state variable and a second state variable based on the COUNT value of the data, wherein the first state variable indicates a COUNT value of a next PDCP PDU expected to be received and the second state variable indicates a COUNT value of a first PDCP PDU not delivered to the upper layer;
comparing the first state variable with the second state variable; and
in case that a value of the first state variable is larger than a value of the second state variable, determining to start the reordering timer.
4. The method of claim 1 , wherein the radio link failure is detected based on at least one of an expiration of a predetermined timer, a random-access failure, a number of times that retransmission is performed reaching a maximum number of retransmissions in a radio link control (RLC) layer, a handover failure, or a failure of reconfiguration with synchronization (reconfiguration with sync).
5. The method of claim 1 , wherein data associated with the split SRB is continued to delivered from the PDCP entity to the upper layer, until a response message for the information is received.
6. The method of claim 5 , wherein the response message comprises a handover command or a command to perform re-establishment of a PDCP associated with the split SRB.
7. The method of claim 1 , further comprising:
suspending transmission of all SRBs or data radio bearers (DRB) transmitted via the MCG based on a detection of the radio link failure; and
resetting a medium access control (MAC) of the MCG.
8. A user equipment (UE) in a wireless communication system, the UE comprising:
a transceiver; and
a controller configured to:
detect a radio link failure of a master cell group (MCG),
control the transceiver to transmit information on the radio link failure via a secondary cell group (SCG),
control the transceiver to receive data, after a transmission of the radio link failure,
in case that the data is received via a split signaling radio bearer (SRB) between the MCG and the SCG, reset and start a reordering timer for the split SRB based on a COUNT value of the data, wherein the reordering timer is used for detecting loss of packet data convergence protocol (PDCP) protocol data unit (PDU), and
deliver, from a PDCP entity to an upper layer, a PDCP service data unit (SDU) associated with the data based on an expiration of the reordering timer,
wherein a value of the reordering timer for the split SRB is reset from infinity to a predetermined value.
9. The UE of claim 8 , wherein the predetermined time is 0.
10. The UE of claim 8
wherein the controller is further configured to:
identify a first state variable and a second state variable based on the COUNT value of the data, wherein the first state variable indicates a COUNT value of a next PDCP PDU expected to be received and the second state variable indicates a COUNT value of a first PDCP PDU not delivered to the upper layer;
compare the first state variable with the second state variable; and
in case that a value of the first state variable is larger than a value of the second state variable, determine to start the reordering timer.
11. The UE of claim 8 , wherein the controller is further configured to detect the radio link failure based on at least one of an expiration of a predetermined timer, a random-access failure, a number of times that retransmission is performed reaching a maximum number of retransmissions in a radio link control (RLC) layer, a handover failure, or a failure of reconfiguration with synchronization (reconfiguration with sync).
12. The UE of claim 8 , wherein the controller is further configured to continue to deliver, from the PDCP entity to the upper layer, data associated with the split SRB, until a response message for the information is received.
13. The UE of claim 12 , wherein the response message comprises a handover command or a command to perform re-establishment of a PDCP associated with the split SRB.
14. The UE of claim 8 , wherein the controller is further configured to suspend transmission of all SRBs or data radio bearers (DRB) transmitted via the MCG and to reset a medium access control (MAC) of the MCG based on a detection of the radio link failure.