6.1 Registration procedure
23.2043GPPRelease 17Stage 2Support of Short Message Service (SMS) over generic 3GPP Internet Protocol (IP) accessTS
Figure 6.1: Registration procedure
1) The UE establishes IP connection.
2) At any time after the establishment of the IP connection, the UE registers at the S-CSCF according to the IMS registration procedures.
NOTE 1: For simplicity, not all messages between UE and S-CSCF and between S-CSCF and HSS are shown in detail.
3) S-CSCF checks the initial filter criteria retrieved from the HSS during the IMS registration procedure.
4) After successful IMS registration and based on the retrieved initial filter criteria, the S-CSCF informs the IP-SM-GW (AS) about the registration of the user. IMSI is informed to the IP‑SM‑GW (AS) when there is no MSISDN in the UE’s IMS subscription profile.
5) The IP-SM-GW (AS) returns OK to the S-CSCF.
6) The IP-SM-GW (AS) sends IP-SM-GW Register Req to the HSS.
7) The HSS stores the received IP-SM-GW address if necessary or for MT-SMS without MSISDN (see clause 6.0a.2), uses it as an indication that the UE is available to be accessed via the IMS to trigger an Alert service centre message if the message waiting flag is set, and responses to the IP-SM-GW (AS) with IP‑SM‑GW Register Res. IP‑SM‑GW gets the IMPU (SIP URI) for SMS delivery without TEL-URI from registration event package.
NOTE 2: IP-SM-GW Register Res can include the SC address to be used for this user in the subscriber data (see also clause 6.7).
NOTE 3: If the IP‑SM‑GW address stored in the HSS via registration procedure is not the same as the preconfigured IP‑SM‑GW address (if any), then the short message delivery attempted during registration can be unnecessarily delayed.
8) After successful registration of the IP‑SM‑GW address at the HSS the HSS checks whether message waiting data are stored and alerts all SCs using procedures described in TS 23.040 [2] (see also clause 6.5b).