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:
determining whether to configure at least one dual active protocol stack (DAPS) bearer based on information for a reconfiguration with synchronization (sync);
establishing, for each signaling radio bearer (SRB), a radio link control (RLC) entity for a target cell group with a same configuration for a source cell group, in case that the at least one DAPS bearer is configured;
establishing, for each SRB, a logical channel for the target cell group with the same configuration for the source cell group;
suspending an SRB for the source cell group;
determining whether the reconfiguration with sync fails;
identifying that the at least one DAPS bearer is configured and a radio link failure is not detected in the source cell group, in case that the reconfiguration with sync fails; and
configuring, for each SRB, a state variable for a packet data convergence protocol (PDCP) entity for the source cell group with a value stored in a PDCP entity for the target cell group in case that a security key is maintained based on the identification.
2. The method of claim 1 , further comprising:
configuring a state variable for the PDCP entity for the target cell group with a value stored in the PDCP entity for the source cell group, in case that a security key is maintained for the SRB for the target cell group.
3. The method of claim 1 , further comprising:
discarding a PDCP service data unit (SDU) in the PDCP entity for the source cell group; and
re-establishing a radio link control (RLC) entity for the source cell group.
4. The method of claim 1 , wherein identifying that the reconfiguration with sync fails further comprising:
identifying that the reconfiguration with sync fails in case that a timer configured by the information expires.
5. The method of claim 2 , wherein the state variable includes at least one of a TX_NEXT indicating a count value of a next PDCP service data unit (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; and
transmitting, to the terminal, the information,
wherein whether to configure at least one dual active protocol stack (DAPS) bearer is determined, by the terminal, based on the information,
wherein, for each signaling radio bearer (SRB), a radio link control (RLC) entity for a target cell group is established with a same configuration for a source cell group, a logical channel for the target cell group is established with the same configuration for the source cell group, and an SRB for the source cell group being suspended, in case that the at least one DAPS bearer is configured, and
wherein, in case that the reconfiguration with sync fails based on the at least one DAPS bearer being configured and a radio link failure being not detected in the source cell group, a state variable for a packet data convergence protocol (PDCP) entity for the source cell group, for each SRB, configured with a value stored in a PDCP entity for the target cell group in case that a security key is maintained.
7. The method of claim 6 ,
wherein a state variable for the PDCP entity for the target cell group is configured with a value of the PDCP entity for the source cell group, in case that a security key is maintained for the SRB for the target cell group.
8. The method of claim 6 ,
wherein a PDCP service data unit (SDU) in the PDCP entity for the source cell group is discarded,
wherein a radio link control (RLC) entity for the source cell group is re-established,
wherein the reconfiguration with sync is identified to failed in case that a timer configured by the information expires, and
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.
9. A terminal in a wireless communication system, the terminal comprising:
a transceiver configured to transmit and receive a signal; and
a controller configured to:
determine whether to configure at least one dual active protocol stack (DAPS) bearer based on information for a reconfiguration with synchronization (sync),
establish, for each signaling radio bearer (SRB), a radio link control (RLC) entity for a target cell group with a same configuration for a source cell group, in case that the at least one DAPS bearer is configured,
establish, for each SRB, a logical channel for the target cell group with the same configuration for the source cell group,
suspend an SRB for the source cell group,
determine whether the reconfiguration with sync fails,
identify that the at least one DAPS bearer is configured and a radio link failure is not detected in the source cell group, in case that the reconfiguration with sync fails, and
configure, for each SRB, a state variable for a packet data convergence protocol (PDCP) entity for the source cell group with a value stored in a PDCP entity for the target cell group in case that a security key is maintained based on the identification.
10. The terminal of claim 9 , wherein the controller is further configured to:
configure a state variable for the PDCP entity for the target cell group with a value stored in the PDCP entity for the source cell group, in case that a security key is maintained for the SRB for the target cell group.
11. The terminal of claim 9 , wherein the controller is further configured to:
discard a PDCP service data unit (SDU) in the PDCP entity for the source cell group, and
re-establish a radio link control (RLC) entity for the source cell group.
12. The terminal of claim 9 , wherein the controller is further configured to:
identify the reconfiguration with sync fails in case that a timer configured by the information expires.
13. The terminal of claim 10 , wherein the state variable includes at least one of a TX_NEXT indicating a count value of next PDCP service data unit (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.
14. 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, and
transmit, to the terminal, the information,
wherein whether to configure at least one dual active protocol stack (DAPS) bearer is determined, by the terminal, based on the information,
wherein for each signaling radio bearer (SRB), a radio link control (RLC) entity for a target cell group is established with a same configuration for a source cell group, a logical channel for the target cell group is established with the same configuration for the source cell group, and an SRB for the source cell group being suspended, in case that the at least one DAPS bearer is configured, and
wherein, in case that the reconfiguration with sync fails based on the at least one DAPS bearer being configured and a radio link failure being not detected in the source cell group, a state variable for a packet data convergence protocol (PDCP) entity for the source cell group, for each SRB, configured with a value stored in a PDCP entity for the target cell group in case that a security key is maintained.
15. The base station of claim 14 , wherein a state variable for the PDCP entity for the target cell group is configured with a value of the PDCP entity for the source cell group, in case that a security key is maintained for the SRB for the target cell group.
16. The base station of claim 14 ,
wherein a PDCP service data unit (SDU) in the PDCP layer device entity for the source cell group is discarded,
wherein a radio link control (RLC) entity for the source cell group is re-established,
wherein the reconfiguration with sync is identified to failed in case that a timer configured by the information expires, and
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.