Method and user equipment for handling user plane in dual connectivity in wireless communication system

1. A method for a user equipment (UE) performing communication with network nodes (NNs) in a wireless communication network, the method comprising:

establishing connections between at least two of the NNs and the UE, the UE configured with an evolved-UMTS terrestrial radio access (E-UTRAN)-new radio access network (NR) dual connectivity (EN-DC), wherein the UE comprises an E-UTRA RLC sublayer and a NR RLC sublayer;

receiving a Radio Resource Control (RRC) reconfiguration message including one or more Layer 2 indications;

identifying, from the one or more Layer 2 (L2) indications, one of:

at least one radio bearer (RB) identity, or

a logical channel (LCH) identity corresponding to a current configuration of the UE; and

in response to an indication of one of: a re-establishment or a release of a radio link control (RLC) sub-layer for the identified one of: the at least one RB or the LCH being obtained, performing the re-establishment or the release of the RLC sub-layer for the identified one of: the at least one RB or the LCH.

2. The method of claim 1 , wherein a split bearer is configured for the RLC sub-layer.

3. The method of claim 1 , further comprising, in response to identifying a data radio bearer (DRB) identity included in the one or more L2 indications being not a part of the current configuration of the UE,

obtaining key indication for the identified DRB identity based on the one or more Layer 2 indications; and

applying a key, based on the key indication, to a packet data convergence protocol (PDCP) sub-layer.

4. The method of claim 1 , further comprising:

obtaining indication for recovery of a PDCP sub-layer based on the one or more L2 indications; and

performing retransmission of PDCP protocol data units (PDUs).

5. The method of claim 4 , wherein performing retransmission comprises retransmitting the PDCP PDUs previously submitted to re-established or released acknowledged mode RLC (AM RLC) sub-layer in ascending order of associated count values from a first PDCP Data PDU for which successful delivery has not been confirmed by lower sub-layers.

6. The method of claim 1 , further comprising:

obtaining the indication for the release of the RLC sub-layer; and

performing a discard of RLC service data units (SDUs) and RLC PDUs and the release of the RLC sub-layer.

7. The method of claim 1 , wherein in response to a MAC sub-layer receiving a MAC PDU for a MAC sub-layer cell-radio network temporary identifier (C-RNTI) or Semi-Persistent Scheduling C-RNTI, discarding a sub-PDU in the received MAC PDU.

8. The method of claim 1 , wherein in response to a MAC sub-layer receiving a MAC PDU containing reserved or invalid values, via a configured downlink assignment, discarding a sub-PDU in the received MAC PDU.

9. A user equipment (UE) for performing communication with network nodes (NNs) in a wireless communication network, the UE comprising:

a transceiver; and

a processor configured to the transceiver and configured to:

establish connections between at least two of the NNs and the UE, the UE configured with an evolved-UMTS terrestrial radio access (E-UTRAN)-new radio access network (NR) dual connectivity (EN-DC), wherein the UE comprises an E-UTRA RLC sublayer and a NR RLC sublayer,

control the transceiver to receive a Radio Resource Control (RRC) reconfiguration message including one or more Layer 2 (L2) indications,

identify, from the one or more Layer 2 indications, one of:

at least one radio bearer (RB) identity, or

a logical channel (LCH) identity corresponding to a current configuration of the UE; and

in response to an indication of one of: a re-establishment, or a release of a radio link control (RLC) sub-layer for the identified one of: the at least one RB or the LCH being obtained, perform the re-establishment or the release of the RLC sub-layer for the identified one of: the at least one RB or the LCH.

10. The UE of claim 9 , wherein a split bearer is configured for the RLC sub-layer.

11. The UE of claim 9 , the processor is further configured to, in response to identifying a data radio bearer (DRB) identity included in the one or more L2 indications being not a part of the current configuration of the UE,

obtain key indication for the identified DRB identity based on the one or more Layer 2 indications; and

apply a key, based on the key indication, to a packet data convergence protocol (PDCP) sub-layer.

12. The UE of claim 9 , wherein the processor is further configured to:

obtain indication for recovery of a PDCP sub-layer based on the one or more L2 indications; and

perform retransmission of PDCP protocol data units (PDUs).

13. The UE of claim 9 , wherein the processor is further configured to:

control the transceiver to retransmit the PDCP PDUs previously submitted to re-established or released acknowledged mode RLC (AM RLC) sub-layer in ascending order of associated count values from a first PDCP Data PDU for which successful delivery has not been confirmed by lower sub-layers.

14. The UE of claim 9 , wherein the processor is further configured to:

obtain the indication for the release of the RLC sub-layer; and

perform a discard of RLC service data units (SDUs) and RLC PDUs and the release of the RLC sub-layer.

15. The UE of claim 9 , wherein the processor is further configured to:

in response to a MAC sub-layer receiving a MAC PDU for a MAC sub-layer cell-radio network temporary identifier (C-RNTI) or Semi-Persistent Scheduling C-RNTI, discard a sub-PDU in the received MAC PDU.

16. The UE of claim 9 , wherein the processor is further configured to:

in response to a MAC sub-layer receiving a MAC PDU containing reserved or invalid values, via a configured downlink assignment, discard a sub-PDU in the received MAC PDU.

17. A first network node (NN) for performing communication with user equipment (UE) in a wireless communication network, the first NN comprising:

a transceiver; and

a processor configured to the transceiver and configured to:

determine one or more Layer 2 (L2) indications including at least one radio bearer (RB) identity or logical channel (LCH) identity, and

control the transceiver to transmit Radio Resource Control (RRC) reconfiguration message including the one or more Layer 2 indications to the UE, wherein the UE is configured with an evolved-UMTS terrestrial radio access (E-UTRAN)-new radio access network (NR) dual connectivity (EN-DC),

wherein the UE comprises an E-UTRA RLC sublayer and a NR RLC sublayer,

wherein:

the at least one RB identity or LCH identity corresponding to a current configuration of the UE is identified at the UE, and

in response to an indication of one of: a re-establishment or a release of a radio link control (RLC) sub-layer, for the identified at least one RB or the identified LCH being obtained at the UE, the RLC sub-layer for the identified RB or the identified LCH is re-established or released.

18. The method of claim 1 ,

wherein the RRC reconfiguration message comprises NR RRC configuration message triggered based on Secondary Cell Group (SCG) change procedure.

19. The UE of claim 9 ,

wherein the RRC reconfiguration message comprises NR RRC configuration message triggered based on Secondary Cell Group (SCG) change procedure.