LTE: What is the role of Authentication Procedure over S6a interface ?

Question

Based on the 3GPP 29.272, the IDR (Insert-Subscriber-data Request message) is generated by the HSS to the MME to update the subscriber profile in the MME and/or requesting subscriber info such as location-information, subscriber state...
However the SUBSCRIPTION-DATA AVP containing the of profile to be added or updated is defined as Mandatory.
What should contain this AVP if the IDR is sent only for requesting subscriber-info without updating the subscriber profile.
Should ot be present without any nested AVP under it?

Answer 1

The S6a interface enables the transfer of subscriber related data between the MME and the HSS

Location Management Procedures

Location Update Procedures: To update location information in the HSS
Cancel Location: To delete a subscriber record from the MME or SGSN
Purge UE: to indicate that the subscriber’s profile has been deleted from the MME or SGSN either by an MMI interaction or automatically

Subscriber Data Handling Procedures

Insert-Subscriber-Data: for updating and/or requesting certain user data in the MME or SGSN
Delete Subscriber Data: to remove some or all data of the HSS user profile stored in the MME or SGSN

Authentication Procedures

Authentication Information Retrieval: to request Authentication Information from the HSS

Fault Recovery Procedure

Reset: The Reset Procedure shall be used by the HSS, after a restart, to indicate to the MME and to the SGSN that a failure has occurred

Notification Procedure

Notification: when an inter MME or SGSN location update does not occur but the HSS needs to be notified