Method and apparatus for supporting link establishment procedure with integrated discovery for ue-to-ue relay communication in a wireless communication system

A relay User Equipment (UE), comprising:

• a control circuit;
• a processor installed in the control circuit;
• a memory installed in the control circuit and coupled to the processor;
• wherein the processor is configured to execute a program code stored in the memory to:
• establish a direct link with a second end UE for supporting a UE-to-UE (U2U) relay communication between a first end UE and the second end UE via the relay UE;
• send, after establishing the direct link between the relay UE and the second end UE, a first message to the first end UE to trigger security establishment between the first end UE and the relay UE;
• receive a second message from the first end UE to establish a security context between the relay UE and the first end UE or to add new PC5 Quality of Service (QoS) information, wherein the second message includes a first PC5 QoS information for supporting the U2U relay communication and a Medium Access Control (MAC) address of the first end UE;
• and
• send, in response to receiving the first PC5 QoS information, a third message to the second end UE for modifying or updating the direct link, wherein the third message includes a second PC5 QoS information for supporting the U2U relay communication and the MAC address of the first end UE included in the second message.