Question: Upon detecting an S5 path failure, what action may an S4-SGSN take to restore a UE's PDN connection if the UE is in connected mode and the S4 path is still available?
Option 1: Initiate a UE-triggered Serving GW relocation procedure
Option 2: Send an immediate PGW Uplink Triggering Notification to the affected UE
Option 3: Perform an S4-SGSN triggered Serving GW relocation procedure
Option 4: Automatically switch the UE to idle mode to conserve network resources
Explanation: When an S5 path failure is detected and the S4 path remains available for a UE in connected mode, the S4-SGSN may proactively restore the PDN connection by initiating a relocation of the Serving GW. This approach ensures continuity of service without relying on UE-initiated actions or simply altering the UE's state, aligning with efficient network management and service restoration principles.