Question: How does an I-CSCF typically determine S-CSCF failure to trigger rerouting of registration requests according to IMS restoration procedures?
Option 1: Through periodic heartbeat signals from the S-CSCF.
Option 2: By receiving a list of unavailable S-CSCFs from the HSS (Home Subscriber Server).
Option 3: Via explicit failure messages or implicit timeouts, as part of its internal monitoring.
Option 4: Based on subscriber location updates received from the MME (Mobility Management Entity).
Explanation: In the context of IMS restoration procedures, an I-CSCF detects S-CSCF failures through explicit failure messages or implicitly via timeouts during internal monitoring. This ensures effective rerouting of registration requests without relying on external updates or unrelated periodic checks.