Question: In E-UTRA/E-UTRAN sidelink discovery, which layers of the Access Stratum protocol stack are involved, and what is a key characteristic of the Discovery PDU generation process?
Option 1: Only PHY layer; No MAC header is added to the Discovery PDU.
Option 2: Both MAC and IP layers; A MAC header is always added for routing.
Option 3: Only MAC and PHY layers; No MAC header is added to the Discovery PDU.
Option 4: All layers (MAC, PHY, IP); The IP layer routes the discovery message.
Explanation: In sidelink discovery for E-UTRA/E-UTRAN, the Access Stratum protocol stack involves only the MAC and PHY layers. A key aspect of the Discovery PDU generation process is that the MAC layer builds the MAC PDU carrying the discovery message without adding a MAC header before sending it to the physical layer for transmission.