Section: 16.2.0 Support for IMS voice
Content: 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[ System architecture for the 5G System (5GS) ]  [3]), or through EPC System fallback; - UE capability to support "IMS voice over PS", see TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [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[ NR; Radio Resource Control (RRC); Protocol specification ]  [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.