Question: What action does the UE take when upper layers request transmission of a PC5-S message for a specific destination on sidelink SRB?
Option 1: The UE establishes only the RLC entity and logical channel for the sidelink SRB.
Option 2: The UE establishes PDCP entity, RLC entity, and the logical channel of a sidelink SRB for PC5-S message.
Option 3: The UE considers the PC5-RRC connection established without any further action.
Option 4: The UE ignores the request as it is not relevant to sidelink SRB.
Explanation: According to the protocol specification, when upper layers request transmission of a PC5-S message for a specific destination on sidelink SRB, the UE must establish PDCP entity, RLC entity, and the logical channel of a sidelink SRB for PC5-S message. This ensures proper handling and transmission of the message over the sidelink interface.