16.2.0 Support for IMS voice

For IMS voice support in NG-RAN, the following is assumed:

• Network ability to support IMS voice sessions, i.e. ability to support QoS flows with 5QI for voice and IMS signalling (see clause 12 and TS 23.501 [3]), or through EPC System fallback;
• UE capability to support "IMS voice over PS", see TS 24.501 [28].

The capabilities indications check is handled at NAS layer. To maintain the voice service in NG-RAN, the UE provides additional capabilities over RRC (see TS 38.331 [12]), that are used to determine accurate NR voice support options.

Further MMTEL IMS voice and video enhancements are facilitated by the mechanisms described in the following clauses.