Step 1.
I-CSCF receives an incoming REGISTER request.
Step 2.
The I CSCF sends the Cx-Query/Cx-Select-Pull to the HSS with the Public User Identity.
Step 3.
Upon reception of Cx-Query, the application specific front-end (HSS-FE) fetches all the user data it needs to perform its application logic (e.g. capabilities associated to the user subscription, list of visited networks allowed, S-CSCF name, etc.) in the UDR through a Ud Query procedure.
Step 4.
After applying the proper access control (i.e. the front-end is allowed to read the type of data), the UDR responds with data requested (user location, required capabilities, etc.).
Step 5.
The HSS-FE includes the S-CSCF name in the response. No user data is kept in the HSS FE.
Step 6.
The I-CSCF sends the REGISTER request to the received S-CSCF.
Step 7.
The S-CSCF sends to HSS Cx-Put/Pull. This request, in this example, is received by a different HSS-FE.
Step 8.
Upon reception of Cx-Put/Pull, the HSS-FE fetches the user profile, S-CSCF name, etc. from the UDR through a Ud Query procedure .
Step 9.
After applying the proper access control, the UDR responds with data requested (e.g. user profile).
Step 10.
The HSS- FE detects that this is a re-registration, so it sends Cx-Put/Pull Resp to S-CSCF. No user data is kept in the front-end after the procedure is ended.
Step 11.
The S-CSCF returns 200 OK to I-CSCF
Step 12.
The I-CSCF forwards the response to P-CSCF.