1. A method for a second User Equipment (UE) operating in a wireless communication system, the method comprising:receiving, by the second UE, a Medium Access Control (MAC) Protocol Data Unit (PDU) including a source identity (ID), a target ID, a plurality of logical channel IDs (LCIDs) and a plurality of MAC Service Data Units (SDUs) from a first UE via an interface,
wherein the interface is configured for one-to-one communication between the second UE and the first UE directly, and
wherein each of the plurality of LCIDs identifying a logical channel for one-to-one communication corresponds to a respective MAC SDU for the logical channel identified by a corresponding LCID; and
delivering the MAC PDU to an upper layer if the target ID matches any one of a plurality of IDs managed by the second UE,
wherein the source ID identifies the first UE, and the target ID identifies the second UE in case of one-to-one communication.