Question: In a GTP-U tunnel, when is an End Marker message(s) sent, except for the case of an E-UTRAN Initiated E-RAB modification procedure?
Option 1: Immediately after receiving any G-PDU on the tunnel
Option 2: After sending the last G-PDU that needs to be sent on the tunnel or after receiving an End Marker Indication
Option 3: During every Inter-MME TAU procedure, regardless of G-PDU transmission
Option 4: Only when initiating the release of corresponding S11-U resources
Explanation: This is correct because End Marker messages are sent to signify the end of data transmission on a GTP-U tunnel. This occurs either after the last necessary G-PDU has been transmitted on the tunnel or upon receiving an indication to mark the end, ensuring proper closure and resource management in EPS.