How does subscriber REGISTRATION in IMS work ?
Rating: +5
1) REGISTER request from UE reached P-CSCF
2) P-CSCF does a DNS look up (what type of record? ) at the domain of request URI to find the address of I-CSCF
3) I-CSCF checks in HSS (UAR and UAA) to see if the user is already registered, if it is not registered then I-CSCF assigns S-CSCF to the user and forwards the REGISTER message to S-CSCF
4) S-CSCF gives a 401 and at the same time via the Cx diameter interface between S-CSCF and HSS send a MAR (Multimedia-Auth-Request) message to HSS to download the profile and auth parameters of the user, HSS replies with MAA Multimedia-Auth-Answer message
5) UE again sends a REGISTER, this time including its auth parameters, S-CSCF matches this with information that it downloaded from HSS, if they match the user gets registered