Method and apparatus for sidelink signaling radio bearer (srb) establishment in a wireless communication system

A first UE (User Equipment) for establishing unicast link, comprising:

• a processor;
• and
• a memory operatively coupled to the processor, wherein the processor is configured to execute a program code to:
• establish a first sidelink Signaling Radio Bearer (SRB) for PC5-S message transmission in response to a unicast link or a PCS-Radio Resource Control (PC5-RRC) connection establishment being initiated, wherein the first sidelink SRB is associated with a default Destination Layer-2 Identity (ID);
• transmit a first PC5-S message for the unicast link or the PC5-RRC connection establishment on the first sidelink SRB with a Source Layer-2 ID derived from a Layer-2 ID of the first UE and a Destination Layer-2 ID derived from the default Destination Layer-2 ID;
• receive a second PC5-S message from a second UE, wherein the second PC5-S message is transmitted with a Source Layer-2 ID derived from a Layer-2 ID of the second UE and a Destination Layer-2 ID derived from the Layer-2 ID of the first UE;
• and
• establish a second sidelink SRB for PC5-S message reception and/or transmission, wherein the second sidelink SRB is associated with the Layer-2 ID of the second UE.