Question: In IMS Restoration Procedures, when an I-CSCF fails to contact an S-CSCF (returned by HSS during a user registration status query) after a UE initiates a SIP REGISTER, what action does the I-CSCF take regarding the HSS?
Option 1: The I-CSCF skips requesting S-CSCF capabilities from the HSS and directly selects a new S-CSCF.
Option 2: The I-CSCF sends a UAR with Authorization Type set to REGISTRATION_ONLY to the HSS.
Option 3: The I-CSCF sends a UAR with Authorization Type set to REGISTRATION_AND_CAPABILITIES to the HSS to explicitly request S-CSCF capabilities.
Option 4: The I-CSCF initiates a failover procedure without involving the HSS for re-assignment.
Explanation: When the I-CSCF is unable to contact the assigned S-CSCF, it needs to request new S-CSCF capabilities from the HSS to facilitate the assignment of another S-CSCF. This ensures seamless continuation of IMS services for the UE. The correct action involves explicitly requesting these capabilities, which aligns with maintaining service integrity and facilitating proper re-routing of the SIP REGISTER to a newly assigned S-CSCF.