Method and apparatus for configuring fallback for each bearer when daps handover fails in next-generation mobile communication system
The disclosure relates to a communication method and system for converging a 5 th -Generation (5G) communication system for supporting higher data rates beyond a 4 th -Generation (4G) system with a technology for Internet of Things (IoT). The disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. The disclosure relates to a method and an apparatus for performing fallback when handover fails in a case where efficient handover without interruption of transmission or reception of data during handover is performed.
1. A method performed by a terminal in a wireless communication system, the method comprising:
receiving, from a base station, information for a reconfiguration with synchronization (sync), the information configuring at least one dual active protocol stack (DAPS) bearer;
establishing a signaling radio bearer (SRB) for a target cell group with a same configuration for a source cell group based on the information, wherein an SRB for the source cell group is suspended; and
configuring an initial value of a state variable for a packet data convergence protocol (PDCP) layer device for the target cell group with a value stored in a PDCP layer device for the source cell group, in case that a security key is maintained for the SRB for the target cell group.
2. The method of claim 1 , further comprising:
identifying that the reconfiguration with sync fails and a radio link failure is not detected in the source cell group; and
configuring an initial value of a state variable for the PDCP layer device for the source cell group with a value stored in the PDCP layer device for the target cell group, in case that the security key is maintained.
3. The method of claim 2 , further comprising:
discarding a PDCP service data unit (SDU) in the PDCP layer device for the source cell group; and
re-establishing a radio link control (RLC) entity for the source cell group.
4. The method of claim 2 , wherein the reconfiguration with sync is identified to have failed based on an expiry of a timer configured by the information.
5. The method of claim 1 , wherein the state variable includes at least one of a TX_NEXT indicating a count value of a next PDCP SDU to be transmitted, an RX_NEXT indicating a count value of a next PDCP SDU expected to be received, an RX_DELIV indicating a count value of a first PDCP SDU not delivered to a higher layer, or an RX_REORD indicating a count value following a count value associated with PDCP data protocol data unit (PDU) which triggered a reordering timer.
6. A method performed by a base station in a wireless communication system, the method comprising:
generating information for a reconfiguration with synchronization (sync) for a terminal, the information configuring at least one dual active protocol stack (DAPS) bearer; and
transmitting, to the terminal, the information,
wherein a signaling radio bearer (SRB) for a target cell group is established with a same configuration for a source cell group based on the information, an SRB for the source cell group being suspended, and
wherein an initial value of a state variable for a packet data convergence protocol (PDCP) layer device for the target cell group is configured with a value of a PDCP layer device for the source cell group, in case that a security key is maintained for the SRB for the target cell group.
7. The method of claim 6 , wherein, in case that the reconfiguration with sync fails and a radio link failure is not detected in the source cell group, an initial value of a state variable for the PDCP layer device for the source cell group is configured with a value of the PDCP layer device for the target cell group, in case that the security key is maintained.
8. The method of claim 7 ,
wherein a PDCP service data unit (SDU) in the PDCP layer device for the source cell group is discarded, and
wherein a radio link control (RLC) entity for the source cell group is re-established.
9. The method of claim 7 , wherein the reconfiguration with sync is identified to have failed based on an expiry of a timer configured by the information.
10. The method of claim 6 , wherein the state variable includes at least one of a TX_NEXT indicating a count value of a next PDCP SDU to be transmitted, an RX_NEXT indicating a count value of a next PDCP SDU expected to be received, an RX_DELIV indicating a count value of first PDCP SDU not delivered to a higher layer, or an RX_REORD indicating a count value following a count value associated with PDCP data protocol data unit (PDU) which triggered a reordering timer.
11. A terminal in a wireless communication system, the terminal comprising:
a transceiver configured to transmit and receive a signal; and
a controller configured to:
receive, from a base station, information for a reconfiguration with synchronization (sync), the information configuring at least one dual active protocol stack (DAPS) bearer,
establish a signaling radio bearer (SRB) for a target cell group with a same configuration for a source cell group based on the information, wherein SRB for the source cell group is suspended, and
configure an initial value of a state variable for a packet data convergence protocol (PDCP) layer device for the target cell group with a value stored in a PDCP layer device for the source cell group, in case that a security key is maintained for the SRB for the target cell group.
12. The terminal of claim 11 , wherein the controller is further configured to:
identify that the reconfiguration with sync fails and a radio link failure is not detected in the source cell group, and
configure an initial value of a state variable for the PDCP layer device for the source cell group with a value stored in the PDCP layer device for the target cell group, in case that the security key is maintained.
13. The terminal of claim 12 , wherein the controller is further configured to:
discard a PDCP service data unit (SDU) in the PDCP layer device for the source cell group; and
re-establish a radio link control (RLC) entity for the source cell group.
14. The terminal of claim 12 , wherein the reconfiguration with sync is identified to have failed based on an expiry of a timer configured by the information.
15. The terminal of claim 11 , wherein the state variable includes at least one of a TX_NEXT indicating a count value of next PDCP SDU to be transmitted, an RX_NEXT indicating a count value of next PDCP SDU expected to be received, an RX_DELIV indicating a count value of first PDCP SDU not delivered to a higher layer, or an RX_REORD indicating count value following count value associated with PDCP data protocol data unit (PDU) which triggered a reordering timer.
16. A base station in a wireless communication system, the base station comprising:
a transceiver configured to transmit and receive a signal; and
a controller configured to:
generate information for a reconfiguration with synchronization (sync) for a terminal, the information configuring at least one dual active protocol stack (DAPS) bearer, and
transmit, to the terminal, the information,
wherein a signaling radio bearer (SRB) for a target cell group is established with a same configuration for a source cell group based on the information, an SRB for the source cell group being suspended, and
wherein an initial value of a state variable for a packet data convergence protocol (PDCP) layer device for the target cell group is configured with a value of a PDCP layer device for the source cell group, in case that a security key is maintained for the SRB for the target cell group.
17. The base station of claim 16 , wherein, in case that the reconfiguration with sync fails and a radio link failure is not detected in the source cell group, an initial value of a state variable for the PDCP layer device for the source cell group is configured with a value of the PDCP layer device for the target cell group, in case that the security key is maintained.
18. The base station of claim 17 ,
wherein a PDCP service data unit (SDU) in the PDCP layer device for the source cell group is discarded, and
wherein a radio link control (RLC) entity for the source cell group is re-established.
19. The base station of claim 17 , wherein the reconfiguration with sync is identified to have failed based on an expiry of a timer configured by the information.
20. The base station of claim 16 , wherein the state variable includes at least one of a TX_NEXT indicating a count value of next PDCP SDU to be transmitted, an RX_NEXT indicating a count value of next PDCP SDU expected to be received, an RX_DELIV indicating a count value of first PDCP SDU not delivered to a higher layer, or an RX_REORD indicating count value following count value associated with PDCP data protocol data unit (PDU) which triggered a reordering timer.