Vo5G (Voice over 5G NR): Advantages and Disadvantages

This page covers the advantages and disadvantages of Voice Over 5G New Radio (Vo5G). It mentions the benefits or advantages of Vo5G and the drawbacks or disadvantages of VoNR.

Introduction

5G NR (New Radio) specifications are categorized into NSA (Non-Standalone) and SA (Standalone). 5G NR NSA and SA specifications were released in Dec. 2017 and June 2018 respectively. Data services primarily drive the evolution of 5G NR, but voice and video services are also essential for the growth of 5G cellular services, similar to 4G LTE and its predecessors 3G/2G.

What is Voice over 5G NR?

4G uses LTE as its radio access technology, while 5G uses NR. Voice/video services over LTE and 5G networks are known as VoLTE and VoNR respectively. Both use different access modes for IMS voice/video services. According to 3GPP, 5G must provide voice & video communication services based on IMS (IP Multimedia Subsystem).

IMS must be installed for VoNR (Voice over NR), VoLTE (Voice over LTE), EPS fallback, and RAT Fallback in 3GPP Release 15 or 5G to 3G SRVCC (Single Radio Voice Call Continuity) in 3GPP Release 16.

5G voice services are provided using 5G RAN (Radio Access Network), 5GC (5G Core) and IMS. IMS manages VoNR calls, including setup, maintenance, and release. SIP (Session Initiation Protocol) is used for signalling between the UE (User Equipment) and IMS.

Other requirements for VoNR include UE PDCP support for RTP/RTCP and RoHC compression, and MAC layer support for DRX mode. VoNR uses QoS flows with 5QI=5 (non-GBR) and 5QI=1 (GBR). Non-GBR (5QI=5) is used for SIP signalling messages with high priority to meet low latency requirements. 5G NR gNB (5G base station) uses RLC-AM mode DRB for SIP signalling and RLC UM mode for voice traffic DRBs.

The following are different ways voice services are supported in the 5G NR system:

• 5G VoNR fallback to VoLTE/2G/3G in DC (Dual Connectivity) mode or NSA (Non Standalone) mode
• Interworking between VoNR and VoLTE
• Interworking between VoNR and 2G/3G
• Interworking between VoNR and VoWiFi
• Seamless Voice over NR in 5G Standalone mode (SA mode)

Benefits or Advantages of Vo5G

The following are the benefits or advantages of Vo5G (Voice over 5G):

• It supports seamless handover (HO) from a 5G cell to a 4G LTE cell and vice versa.
• It uses ICS (IMS Centralized Service), which allows 3G HO and prevents call drops when 5G is not available and 3G is available. This enables voice call continuity between 5G and 3G.
• Voice calls are faster in 5G NR due to its low latency.
• Voice calls have better quality due to the use of EVS and H.265 codecs compared to VoLTE.
• Voice over NR and high-speed data services are possible simultaneously.
• It improves voice coverage in the uplink direction due to dual connectivity (DC). Voice calls fall back to the 4G LTE network when 5G services are unavailable.

Drawbacks or Disadvantages of VoNR

The following are the drawbacks or disadvantages of VoNR (Voice over NR):

• It does not support 2G/3G. Hence, 5G NR does not support seamless handover to 2G/3G networks.
• It does not support circuit-switched voice calls.
• Smartphones with 5G NR (VoNR) and 4G LTE (VoLTE) are expensive.
• It takes more time during call setup as it falls back to 4G LTE from 5G NR.