Question: What is the primary purpose of the Nnssf_NSSAIAvailability service in the 5G system?
Option 1: To update the AMFs and NSSF on the availability of S-NSSAIs and NSAGs on a per UE basis.
Option 2: To enable updates for Network Slice Replacement and Network Slice Instance Replacement to the NF Service Consumer when the NSSF determines that an S-NSSAI has to be replaced with an Alternative S-NSSAI or a Network Slice instance is replaced.
Option 3: To provide the serving network and Access Type from the TAI to the NSSF.
Option 4: To update the AMFs and the NSSF on the availability of S-NSSAIs and NSAGs on a per Tracking Area (TA) basis.
Explanation: The correct answer is Option 4 because the primary purpose of the Nnssf_NSSAIAvailability service is to update the AMFs and the NSSF on the availability of S-NSSAIs and NSAGs on a per Tracking Area (TA) basis, as stated in the service description. This service enables the NSSF to provide updates for Network Slice Replacement and Network Slice Instance Replacement to the NF Service Consumer when necessary.