VoNR Glossary

Technical definitions for VoNR, 5G Core, and related terms. For VoLTE-specific terms (IMS, P-CSCF, S-CSCF, AMR-WB, SRVCC, ISIM), see the VoLTE Glossary at voltesim.co.uk.

5GC (5G Core)

The core network architecture for 5G Standalone. Uses a service-based architecture (SBA) with HTTP/2 interfaces between network functions. Comprises AMF, SMF, UPF, PCF, UDM, AUSF, and other functions. Required for VoNR. The 5G equivalent of the 4G EPC.

5G NSA (Non-Standalone)

A 5G architecture option (Option 3x) where the 5G NR radio is used for data alongside a 4G LTE anchor, but the core network is still the 4G EPC. Voice calls on 5G NSA phones use VoLTE on the LTE bearer. VoNR is not possible on 5G NSA.

5G SA (Standalone)

A 5G architecture where both the radio (gNB / NG-RAN) and core network (5GC) are 5G. Required for VoNR. Enables network slicing, edge UPF deployment, and native IMS integration for voice over the 5G NR air interface.

5QI (5G QoS Indicator)

The QoS class identifier used in the 5G QoS model, replacing the LTE QCI. 5QI 1 is the GBR flow used for VoNR conversational voice, with the same parameters as LTE QCI 1: priority 2, 100ms packet delay budget, 10^-2 packet error rate.

AMF (Access and Mobility Management Function)

5GC network function handling UE registration, access authentication, and mobility management. Replaces the 4G MME for control plane functions.

AUSF (Authentication Server Function)

5GC function handling authentication of UEs on the 5G network. Works with the UDM to provide authentication vectors.

EPS Fallback

The mechanism that transfers a VoNR call to VoLTE on an LTE bearer if 5G SA coverage is lost. The 5G equivalent of SRVCC. Ensures voice continuity as devices move between 5G SA and LTE coverage areas.

eSIM / eUICC

Embedded SIM / Embedded Universal Integrated Circuit Card. A remotely programmable SIM that can carry ISIM credentials for VoNR/VoLTE in the same way as a physical SIM card. See euicc.co.uk for full technical reference.

EVS (Enhanced Voice Services)

The primary voice codec for VoNR. Defined in 3GPP TS 26.441. Supports narrowband, wideband, super-wideband (50 Hz – 14.4 kHz), and fullband (20 Hz – 20 kHz) audio. Superior to AMR-WB in both frequency range and packet loss resilience.

gNB

Next Generation NodeB. The 5G NR base station, equivalent to the 4G eNodeB. Connects to the 5GC (AMF and UPF) via the NG interface. Manages the 5G NR radio in NG-RAN.

IMS (IP Multimedia Subsystem)

The SIP-based multimedia session management framework used for VoLTE and VoNR. The same IMS architecture serves both 4G and 5G voice. See voltesim.co.uk for full IMS technical reference.

ISIM (IMS Subscriber Identity Module)

Logical application on the UICC storing IMS credentials (IMPI, IMPU). Required for VoLTE and VoNR. Standard IoT data SIMs do not include ISIM. See voltesim.co.uk/volte-sim-cards.

Network Slicing

5G capability to partition a physical network into logical slices with dedicated resources and QoS. VoNR can be delivered on a dedicated voice slice with guaranteed bandwidth, latency, and packet loss parameters – enabling audio quality SLAs for enterprise deployments.

NG-RAN (Next Generation Radio Access Network)

The 5G SA radio access network comprising gNBs. Connects to the 5GC via the NG interface (N2 for control, N3 for user plane).

PCF (Policy Control Function)

5GC function providing policy and QoS rules. Authorises 5QI 1 GBR flow for VoNR calls. Replaces the 4G PCRF.

SMF (Session Management Function)

5GC function managing PDU sessions and QoS flows. Establishes and modifies the 5QI 1 GBR flow for VoNR voice calls. Replaces 4G MME/PGW session management functions.

UDM (Unified Data Management)

5GC subscriber data repository combining HSS and PCRF functions from 4G. Provides subscriber profiles, IMS identities, and authentication data for VoNR.

UPF (User Plane Function)

5GC function forwarding user-plane packets including RTP voice media for VoNR calls. Can be deployed at the network edge for lower latency. Replaces the 4G SGW/PGW user plane.

URLLC (Ultra-Reliable Low Latency Communications)

A 5G service category targeting 1ms latency and 99.999% reliability. While VoNR voice does not specifically require URLLC, 5G SA’s URLLC capability underpins the low-latency potential for future voice-over-5G applications in industrial and critical communications settings.

VoNR (Voice over New Radio)

The 3GPP-standardised mechanism for delivering voice calls over the 5G New Radio (NR) air interface on a 5G Standalone network, using the IMS for call control and the EVS codec for audio. Defined from 3GPP Release 15. Requires 5G SA – does not work on 5G NSA.