3GPP 24.501 v20.0.0 — the document's own text
4.3.4 Change or determination of IMS voice availability
If the UE operates in single-registration mode, whenever the IMS voice availability is determined or changes, the UE shall execute procedures according to table 4.3.4.1:
Table 4.3.4.1: Change of IMS voice availability for a UE in single-registration mode
| Change of IMS voice available condition | Procedure to execute |
|---|---|
| "IMS voice not available" over NG-RAN access only and the UE's usage setting is "voice centric" | Disable the N1 mode capability for 3GPP access, if the UE is only registered over 3GPP access (see clause 4.9.2). (NOTE 2) |
| "IMS voice not available" over satellite NG-RAN and the UE's usage setting is "voice centric" | Disable the satellite NG-RAN capability. |
| "IMS voice not available" over non-3GPP access only and the UE's usage setting is "voice centric" | Disable the N1 mode capability for non-3GPP access (see clause 4.9.3), if the UE is only registered over non-3GPP access. (NOTE 2) |
| "IMS voice not available" over both NG-RAN access and non-3GPP access, and the UE's usage setting is "voice centric" | Disable the N1 mode capability for 3GPP access (see clause 4.9.2) and non-3GPP access (see clause 4.9.3), if the UE is registered over both 3GPP access and non-3GPP access.Disable the N1 mode capability for 3GPP access (see clause 4.9.2), if the UE is only registered over 3GPP accessDisable the N1 mode capability for non-3GPP access (see clause 4.9.3), if the UE is only registered over non-3GPP access.(NOTE 1, NOTE 2) |
| NOTE 1: If the UE is registered over 3GPP access and has a persistent PDU session, then the UE waits until the radio bearer associated with the persistent PDU session has been released.NOTE 2: If the UE determines "IMS voice not available" upon receipt of a 5GS session management reject message including a back-off timer value, and the re-attempt indicator indicates that the UE is not allowed to re-attempt the procedure in S1 mode then, upon inter-system change from N1 mode to S1 mode, the UE proceeds as specified in 3GPP TS 24.301 [15], clause 4.3.2.4, Change or determination of IMS registration status. |