 and terminate real-time applications such as voice, video, and messaging. From a Quality of Service (QoS) perspective, it is critical that signaling cannot be delayed or dropped. In VoNR, SIP is transported through the 5G system, and the 5G system is responsible for meeting the necessary QoS requirements. Once the call is initiated, associated voice packets are carried by the 5G system in the form of a Real- time Transport Protocol (RTP). It is possible to drop some voice packets without degrading the call quality. However, minimizing the latency for the voice packets is crucial. The different QoS types for signaling and voice packets require the employment of QoS flows with different characteristics, hence different 5G QoS Identifier (5QI) values. VoNR uses the QoS flows with 5QI value 5 for SIP signaling and 5QI value 1 for voice packets. The different characteristics those two 5QI values are shown in the following table (3GPP TS 23.501): VoNR high-level architecture Resource Default Packet Packet Default Services Priority Delay Budget Error Averaging Loss Rate Window 100ms 200 ms Conversational voice Non-GBR 100ms 0.0000001 Not applicable Ims signaling Figure 8.1 - Characteristics of the 5QI values The following diagram shows the established QoS flows of SIP signaling and voice packets required for VoNR: QoS Flow for SIP Signaling QoS Flow for Voice Packet PDU Session Figure 8.2 - 5G access and core networks QoS flows are established in power distribution unit (PDU) sessions, and a PDU session creates connectivity between the device, the gNodeB (gNB), and the User Plane Function (UPF). The UPF provides connectivity to the IMS with an N6 reference point to allow subscribers to conduct calls. IP multimedia subsystem The IMS is the control infrastructure that provides call control services, and it consists of many separate elements such as Call Session Control Functions (CSCFs) and some application servers, and it utilizes some core network nodes. Voice over New Radio (VoNR) CSCFs comprise Proxy CSCF (P-CSCF), I