Method and apparatus for supporting UE-to-network relay communication in a wireless communication system

1. A method for a second User Equipment (UE) to establish one-to-one connection between a first UE and the second UE, comprising:

initiating a first procedure of establishing the one-to-one connection with the first UE for a unicast communication between the first UE and the second UE or for a UE-to-UE communication between the first UE and a third UE via the second UE or a second procedure of establishing the one-to-one connection with the first UE for a UE-to-Network communication between the first UE and a network node via the second UE;

transmitting a first PC5-S message to the first UE for completing the first procedure of establishing the one-to-one connection with the first UE for the unicast communication or the UE-to-UE communication if the first procedure is initiated, wherein the first PC5-S message includes Quality of Service (QoS) information for the unicast communication or the UE-to-UE communication; and

transmitting a second PC5-S message to the first UE for completing the second procedure of establishing the one-to-one connection with the first UE for the UE-to-Network communication if the second procedure is initiated, wherein the second PC5-S message does not include any QoS information for the UE-to-Network communication.

2. The method of claim 1 , further comprising:

receiving a third PC5-S message from the first UE for initiating the first procedure of establishing the one-to-one connection or the second procedure of establishing the one-to-one connection.

3. The method of claim 2 , wherein the third PC5-S message is a Direct Communication Request message or a Direct Link Establishment Request message, and the first or second PC5-S message is a Direct Communication Accept message or a Direct Link Establishment Accept message.

4. The method of claim 1 , further comprising:

transmitting a fourth PC5-S message to the first UE for establishing a first security context for the one-to-one connection in the first procedure of establishing the one-to-one connection or for establishing a second security context for the one-to-one connection in the second procedure of establishing the one-to-one connection; and

receiving a fifth PC5-S message from the first UE for completing establishment of the first security context in the first procedure of establishing the one-to-one connection or for completing establishment of the second security context in the second procedure of establishing the one-to-one connection.

5. The method of claim 4 , wherein the fourth PC5-S message is a Security Mode Command message or a Direct Link Security Mode Command message, and wherein the fifth PC5-S message is a Security Mode Complete message or a Direct Link Security Mode Complete message.

6. The method of claim 1 , wherein a presence of the QoS information in the first or second PC5-S message is defined as optional.

7. The method of claim 1 , wherein a presence of the QoS information in the first PC5-S message is defined as mandatory.

8. The method of claim 1 , wherein the QoS information is not defined in the second PC5-S message.

9. A method for a second User Equipment (UE) to establish one-to-one connection between a first UE and the second UE, comprising:

receiving a first PC5-S message from the first UE for initiating a procedure of establishing the one-to-one connection;

transmitting a second PC5-S message to the first UE for establishing a security context between the first UE and the second UE in the procedure of establishing the one-to-one connection;

receiving a third PC5-S message from the first UE for completing establishment of the security context in the procedure of establishing the one-to-one connection; and

transmitting a fourth PC5-S message to the first UE for completing the procedure of establishing the one-to-one connection, wherein a presence of Quality of Service (QoS) information in the fourth PC5-S message is defined as optional.

10. The method of claim 9 , wherein the fourth PC5-S message includes a QoS information if the one-to-one connection is used for a unicast communication between the first UE and the second UE or a UE-to-UE communication between the first UE and a third UE via the second UE, and the fourth PC5-S message does not include any QoS information if the one-to-one connection is used for a UE-to-Network communication between the first UE and a network node via the second UE.

11. The method of claim 9 , wherein the first PC5-S message is a Direct Communication Request message or a Direct Link Establishment Request message, and the fourth PC5-S message is a Direct Communication Accept message or a Direct Link Establishment Accept message.

12. The method of claim 9 , wherein the second PC5-S message is a Security Mode Command message or a Direct Link Security Mode Command message, and the third PC5-S message is a Security Mode Complete message or a Direct Link Security Mode Complete message.

13. A second 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:

initiate a first procedure of establishing the one-to-one connection with a first UE for a unicast communication between the first UE and the second UE or for a UE-to-UE communication between the first UE and a third UE via the second UE or a second procedure of establishing the one-to-one connection with the first UE for a UE-to-Network communication between the first UE and a network node via the second UE;

transmit a first PC5-S message to the first UE for completing the first procedure of establishing the one-to-one connection with the first UE for the unicast communication or the UE-to-UE communication if the first procedure is initiated, wherein the first PC5-S message includes Quality of Service (QoS) information for the unicast communication or the UE-to-UE communication; and

transmit a second PC5-S message to the first UE for completing the second procedure of establishing the one-to-one connection with the first UE for the UE-to-Network communication if the second procedure is initiated, wherein the second PC5-S message does not include any QoS information for the UE-to-Network communication.

14. The second UE of claim 13 , wherein the processor is further configured to execute a program code stored in the memory to:

receive a third PC5-S message from the first UE for initiating the first procedure of establishing the one-to-one connection or the second procedure of establishing the one-to-one connection.

15. The second UE of claim 14 , wherein the third PC5-S message is a Direct Communication Request message or a Direct Link Establishment Request message, and the first or second PC5-S message is a Direct Communication Accept message or a Direct Link Establishment Accept message.

16. The second UE of claim 13 , wherein the processor is further configured to execute a program code stored in the memory to:

transmit a fourth PC5-S message to the first UE for establishing a first security context for the one-to-one connection in the first procedure of establishing the one-to-one connection or for establishing a second security context for the one-to-one connection in the second procedure of establishing the one-to-one connection; and

receive a fifth PC5-S message from the first UE for completing establishment of the first security context in the first procedure of establishing the one-to-one connection or for completing establishment of the second security context in the second procedure of establishing the one-to-one connection.

17. The second UE of claim 16 , wherein the fourth PC5-S message is a Security Mode Command message or a Direct Link Security Mode Command message, and wherein the fifth PC5-S message is a Security Mode Complete message or a Direct Link Security Mode Complete message.

18. The second UE of claim 13 , wherein a presence of the QoS information in the first or second PC5-S message is defined as optional.

19. The second UE of claim 13 , wherein a presence of the QoS information in the first PC5-S message is defined as mandatory.

20. The second UE of claim 13 , wherein the QoS information is not defined in the second PC5-S message.