Voice over New Radio (VoNR)

The combination of Voice over Long-Term Evolution (VoLTE) and Voice over NR (VoNR) will be the long-term voice infrastructure for mobile service providers. In this chapter, we will discuss the main concepts behind future VoNR networks. Furthermore, VoNR will be analyzed from end to end with a focus on the architecture requirements, initial procedures, call establishment, and interworking.

VoNR has got some very close similarities to VoLTE. For example, both technologies require an IP Multimedia Subsystem (IMS) for call signaling, and both technologies employ their Radio Access Network (RAN), transport, and core networks to carry voice media in the form of IP packets.

We’ll go through the following topics in this chapter:

• VoNR concepts and drivers
• VoNR high-level architecture
• VoNR initial procedures
• VoNR call procedures
• Interworking and voice call continuity

VoNR concepts and drivers

In this section, the concepts and drivers associated with VoNR are analyzed in three main areas: IMS network deployment growth, 5G system service requirements, and ultra-high-definition audio.

IMS network deployments growth

The number of subscribers associated with packet voice services over telephony such as VoLTE is rising significantly. According to the 2018 Ericsson Mobility Report (https://www.ericsson.com/491e17/assets/local/mobility-report/documents/2018/ericsson-mobility-report-june-2018.pdf), VoLTE subscriptions are projected to reach 5.4 billion in 2023, which means that the service providers will be implementing more IMS deployments for VoLTE services. The same IMS architecture can also be employed for VoNR services when a service provider deploys a 5G network. therefore, leveraging existing IMS deployments will be a key driver for VoNR.

5G system service requirements

The 3rd Generation Partnership Project (3GPP) technical specification...

VoNR high-level architecture

There are three main components associated with the VoNR architecture. These are the 5G New Radio (NR) access network, 5G core network (5GC), and IP multimedia subsystem.

5G NR access and core networks

5G NR access and core networks transport call signaling and voice packets.

Call signaling is performed as a Session Initiation Protocol (SIP). SIP is the control signaling used between the device and the IMS to initiate, maintain, 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...

VoNR initial procedures

Before the device can conduct VoNR calls, it must pass through a series of initial procedures. These procedures are as follows:

• Subscriber provisioning
• IMS connectivity establishment
• IMS registration
• Third-party registration

Subscriber provisioning

Several network elements must be provisioned appropriately with subscriber information for VoNR services. Some of these elements are the UDM, the Home Subscriber Server (HSS), the TAS and Service Centralization and Continuity (SCC) application servers, the Policy Control Function (PCF), and AAA servers in case of Wi-Fi calling.

The information indicating whether a subscriber is permitted access to the IMS for voice services is contained within the subscriber profile in the UDM, which acts as a central repository of subscriber information. The subscriber profile contains appropriate QoS profiles for the subscriber, and it also contains whether roaming is supported. Likewise, the UDM...

VoNR call procedures

This section evaluates the activities that need to take place to ultimately set up a VoNR call.

High-level call procedure activities

Key procedures take place within the 5G system, IMS, and policy charging control elements such as PCF to make a VoNR call. There is activity taking place with the SIP and the IMS. There is also activity taking place with the Diameter protocol and PCF. Moreover, there is also activity taking place in the 5G access network itself. Hence, these three network domains work together to establish a VoNR call.

To go into this in more detail, the process starts with the concept of exchanging the Session Description Protocol (SDP) messages: SDP Offer and SDP Answer. A flow of VoIP packets is required between two parties in a VoIP call. Therefore, the IP address and ports between the two parties should be known. Moreover, the voice codec and required bandwidth that need to be used should also be known. The SIP doesn’t do this...

Interworking and voice call continuity

Interworking is required between VoNR-capable networks and the other legacy networks due to legacy subscribers, coverage gaps, and utilization of other radio technologies.

The subscribers of 2G, 3G, and fixed-lined subscribers on Public Switched Telephone Networks (PSTN) do not support SIP signaling. Therefore, the communication between legacy subscribers and a VoNR subscriber requires appropriate SIP-based signaling and Real-Time Transport Protocol (RTP)-based voice packet conversion.

In the rollout of each new technology, there exist some coverage gaps in RANs. So, in these coverage gaps, the subscribers need to hand over to other technologies for connectivity continuity. This is also valid for 5G rollouts. As the 5G networks roll out, there will be some coverage gaps that affect the VoNR subscribers in terms of call continuity. Therefore, some handover techniques from 5G to legacy networks, such as 4G or 3G, are required.

Finally,...

Summary

In summary, we have looked at some of the key concepts and drivers behind VoNR. Circuit-switched networks are slowly being phased out and replaced with voice networks supported by IMS call control. The voice requirements for the 5G system have been defined, so the standard bodies, specifically the 3GPP, have already been looking at what the 5G system needs to support with respect to voice. There is already a great deal of interest in ultra-high-definition voice services.

We have also looked at VoNR’s high-level system architecture. It is comprised of three elements: the 5G access network, the IMS, and Policy and Charging Control (PCC). With respect to the 5G access network, we have looked at some key elements such as the gNB, UPF, AMF, SMF, and UDM. Regarding IMS, we have seen there are elements such as CSCFs, HSS, SCC, and TAS.

We have also analyzed VoNR’s initial procedures. Before making and receiving calls, the VoNR subscribers must conduct these initial...