Question: What protocol is used to tunnel user data between eNodeB and the S-GW, as well as between the S-GW and the P-GW in the backbone network?
Option 1: UDP/IP
Option 2: LTE-Uu
Option 3: MME
Option 4: GTP-U
Explanation: The correct answer is GTP-U (GPRS Tunnelling Protocol for the user plane) because it is specifically designed to tunnel user data between eNodeB and the S-GW, as well as between the S-GW and the P-GW in the backbone network. This protocol encapsulates all end-user packets, ensuring secure and efficient transmission of user data.