Voice Over NR call flow

With the large scale 5G deployment, the voice over NR (VoNR) solution can be used. NR UEs can directly perform voice services on an NR network without falling back to an LTE network.

So the Voice services using 5G RAN, 5G Core and IMS is referred to as Voice over New Radio-VoNR and This solution improves both voice service quality and data services rates.

VoNR Call Flow: 

The VoNR bearer setup and release  process is as follows:

1. When a UE initiates a call, an RRC connection is set up between the calling UE and its serving gNodeB.
2. The 5G core network (5GC) sets up a quality of service (QoS) flow with a 5G QoS Identifier (5QI) of 5 for the calling UE to carry Session Initiation Protocol (SIP) signaling, and the gNodeB sets up the corresponding data radio bearer (DRB).
3. An RRC connection is set up between the UE that receives the call and its serving gNodeB.
4. The 5GC sets up a QoS flow with a 5QI of 5 for the called UE to carry SIP signaling, and the gNodeB sets up the corresponding DRB.
5. The calling and called UEs and the IMS perform SIP negotiation on the codec scheme, IP address, port number, information of both calling and called UEs, and other voice service information.
6. After SIP negotiation is successful, the 5GC sets up QoS flows with a 5QI of 1 for both the calling and called UEs to carry Real-Time Transport Protocol (RTP) and Real-Time Transport Control Protocol (RTCP) data flows, and the gNodeBs set up the corresponding DRBs.
7. After the call ends, the calling and called UEs release their QoS flows with a 5QI of 1, and the gNodeBs release the corresponding DRBs. The default bearers with a 5QI of 5 are released only when the UEs enter the idle state.