Method and apparatus for quality of service (QOS) flow establishment in a wireless communication system

1. A method for Quality of Service (QoS) flow establishment, comprising:

a relay User Equipment (UE) establishes a PC5 unicast link with a remote UE;

the relay UE receives an identifier of a PC5 QoS flow and a first PC5 5G QoS Identifier (PQI) of the PC5 QoS flow from the remote UE for adding the PC5 QoS flow, wherein the first PQI indicates end-to-end QoS requirements of the PC5 QoS flow for traffic transmission between the remote UE and a network;

the relay UE derives a second PQI for the PC5 QoS flow and a 5G QoS Identifier (5QI) for a QoS flow according to the first PQI;

the relay UE transmits a Protocol Data Unit (PDU) Session Modification Request message to the network for adding the QoS flow, wherein the PDU Session Modification Request message includes an identifier of the QoS flow and the 5QI;

the relay UE receives a PDU Session Modification Command message from the network, wherein the PDU Session Modification Command message includes the identifier of the QoS flow and an authorized 5QI for the QoS flow;

the relay UE derives a third PQI for the PC5 QoS flow according to the authorized 5QI if the authorized 5QI is different from the 5QI; and

the relay UE transmits the identifier of the PC5 QoS flow and the second PQI to the remote UE if the authorized 5QI is same as the 5QI and the relay UE transmits the identifier of the PC5 QoS flow and the third PQI to the remote UE if the authorized 5QI is different from the 5QI.

2. The method of claim 1 , wherein the relay UE does not transmit the second PQI to the remote UE before reception of the PDU Session Modification Command message from the network.

3. The method of claim 1 , wherein the second PQI and the 5QI are derived according to the first PQI and QoS mapping.

4. The method of claim 3 , wherein the QoS mapping is pre-configured or provided to the relay UE by the network.

5. The method of claim 1 , wherein the third PQI is derived according to the authorized 5QI and QoS mapping.

6. The method of claim 1 , wherein the identifier of the PC5 QoS flow and the first PQI of the PC5 QoS flow are received in a Direct Link Modification Request message.

7. The method of claim 1 , wherein the identifier of the PC5 QoS flow and the second PQI or the third PQI are transmitted in a Direct Link Modification Accept message.

8. The method of claim 1 , wherein the QoS flow corresponds to the PC5 QoS flow.

9. The method of claim 1 , wherein a Protocol Data Unit (PDU) session is established by the relay UE for the remote UE to access a service from the network via the relay UE.

10. The method of claim 1 , wherein the relay UE is a Layer-3 UE-to-Network Relay UE.

11. A relay UE (User Equipment), comprising:

a control circuit;

a processor installed in the control circuit; and

a memory installed in the control circuit and operatively coupled to the processor;

wherein the processor is configured to execute a program code stored in the memory to:

establish a PC5 unicast link with a remote UE;

receive an identifier of a PC5 QoS flow and a first PC5 5G QoS Identifier (PQI) of the PC5 QoS flow from the remote UE for adding the PC5 QoS flow, wherein the first PQI indicates end-to-end QoS requirements of the PC5 QoS flow for traffic transmission between the remote UE and a network;

derive a second PQI for the PC5 QoS flow and a 5G QoS Identifier (5QI) for a QoS flow according to the first PQI;

transmit a Protocol Data Unit (PDU) Session Modification Request message to the network for adding the QoS flow, wherein the PDU Session Modification Request message includes an identifier of the QoS flow and the 5QI;

receive a PDU Session Modification Command message from the network, wherein the PDU Session Modification Command message includes the identifier of the QoS flow and an authorized 5QI for the QoS flow;

derive a third PQI for the PC5 QoS flow according to the authorized 5QI if the authorized 5QI is different from the 5QI; and

transmit the identifier of the PC5 QoS flow and the second PQI to the remote UE if the authorized 5QI is same as the 5QI and the relay UE transmits the identifier of the PC5 QoS flow and the third PQI to the remote UE if the authorized 5QI is different from the 5QI.

12. The relay UE of claim 11 , wherein the relay UE does not transmit the second PQI to the remote UE before reception of the PDU Session Modification Command message from the network.

13. The relay UE of claim 11 , wherein the second PQI and the 5QI are derived according to the first PQI and QoS mapping.

14. The relay UE of claim 13 , wherein the QoS mapping is pre-configured or provided to the relay UE by the network.

15. The relay UE of claim 11 , wherein the third PQI is derived according to the authorized 5QI and QoS mapping.

16. The relay UE of claim 11 , wherein the identifier of the PC5 QoS flow and the first PQI of the PC5 QoS flow are received in a Direct Link Modification Request message.

17. The relay UE of claim 11 , wherein the identifier of the PC5 QoS flow and the second PQI or the third PQI are transmitted in a Direct Link Modification Accept message.

18. The relay UE of claim 11 , wherein the QoS flow corresponds to the PC5 QoS flow.

19. The relay UE of claim 11 , wherein a Protocol Data Unit (PDU) session is established by the relay UE for the remote UE to access a service from the network via the relay UE.

20. The UE of claim 11 , wherein the relay UE is a Layer-3 UE-to-Network Relay UE.