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Let's talk about VoNR today.

First of all, let's briefly review the evolution history of voice service. The past is the mirror of the future. Before understanding the VoNR in the 5G era, it is necessary to review the evolution history of mobile network voice services.

In the 2G and 3G era, the voice service adopts CS (Circuited Switched) technology, that is, the mobile phone needs to establish a line with exclusive resources in the network before the call, and it will not be removed until the end of the call. This ancient technology has some shortcomings, such as resource consumption, complex networking, low efficiency and so on.

Entering the era of 4G full IP, because there is only packet domain PS, traditional CS voice is no longer supported, so two schemes, CSFB and VoLTE, are proposed to support voice services.

CSFB, that is, CS FallBack, means that when a mobile phone initiates a voice call in a 4G network, it falls back from the LTE network to the 2max 3G network, uses the CS circuit domain of the 2max 3G network to complete the voice call, and then returns to 4G LTE after the call.

VoLTE, namely Voice over LTE, refers to the direct provision of IP-based voice services through the introduction of IMS,LTE network. VoLTE is also called VoIP managed by IMS and carried on 4G LTE network.

VoLTE encapsulates voice services into IP packets and transmits them like express packages without "monopolizing resources", which greatly improves the efficiency of the network. More importantly, VoLTE has unprecedentedly improved voice quality and reduced call setup time.

VoLTE uses AMR-WB (Adaptive Multi-rate-Wideband, Adaptive Multi-rate Broadband coding) voice coding technology, which greatly increases the coding rate compared with 2G and 3G, and increases the voice bandwidth range from 300Hz-3400Hz to 50Hz-7000Hz, thus providing clearer sound quality and wider voice range, making the voice quality of mobile networks comparable to the experience of listening to the radio for the first time. When dialing, the 3G network takes about 6-8 seconds to connect, while VoLTE only takes about 2-3 seconds to connect.

Therefore, in terms of technical architecture and user experience, VoLTE is a revolutionary technological evolution in the history of mobile network voice service development.

Will 5G voice make a huge leap like VoLTE again? What does VoNR look like in the 5G era?

What is VoNR? The ultimate solution of 5G voice will answer the first question first. the voice of 5G era will never change as revolutionarily as VoLTE. In fact, the 5G system does not provide a separate technical solution for voice services, and its design goal is mainly to support the continuous evolution of VoLTE.

As we all know, IMS is the "brain" of VoLTE. VoLTE is actually an end-to-end VoIP connection controlled and managed by the IMS core network. It is precisely because IMS can achieve end-to-end QoS management of voice, so that the voice quality of VoLTE is far better than the "best-effort" Internet VoIP.

Entering the 5G era, when 3GPP defined 5G in R15, it was clear that 5G still provides voice services based on IMS, and determined the design principle that 5G deployment should minimize the impact on the existing IMS.

Based on the above principles, according to the two major deployment options of 5G NSA and SA, 5G Voice provides three deployment solutions: VoLTE, EPS Fallback and VoNR.

VoLTE (NSA networking) under NSA networking, 5G NR is added to the existing 4G network as a capacity expansion, and the 4G core network EPC,4G network is still the main control network. 5G NR only supports best-effort data transmission.

VoLTE (NSA networking) under such an architecture, voice services are still provided by the existing 4G IMS / VoLTE network with very small changes or no changes; voice calls can still be seamlessly switched between VoLTE and 2G / 3G CS networks through SRVCC; if operators do not deploy IMS, they can still fall back to 2G or 3G networks to provide voice services through CS Fallback.

VoLTE Voice continuity guarantee EPS Fallback (SA networking) under SA networking, the 5G network has its own core network 5GC, which no longer depends on 4G as the control network, which means that 5G voice services can be carried independently through 5G NR, 5GC and IMS end-to-end, namely VoNR (Voice over NR) or Vo5G (Voice over 5GS).

However, in the early stage of the deployment of 5G SA, considering that the 5G NR network has not yet formed continuous wide coverage, when the mobile phone moves out of the 5G NR coverage area, it will frequently switch the ongoing VoNR voice to the VoLTE network with better coverage, resulting in poor user experience. Therefore, the transition scheme, EPS Fallback, was introduced in the early stage of 5G deployment.

EPS Fallback (SA networking) is similar to CS Fallback in the 4G era. Under the EPS Fallback scheme, the 5G network does not provide PS voice service. When the mobile phone tries to use the voice service in the 5G network, it will fall back to the 4G network by redirection or switching, and the 4G network will provide VoLTE voice service, and then return to the 5G network after the call. During the call, as the mobile phone has fallen back to the 4G network, the data service is also forced to transmit through the 4G LTE together with the voice service until the call is over.

EPS Fallback voice continuity guarantee obviously, under this scheme, because the voice call is initiated to fall back to the 4G network when the voice call is established on the NR, it is bound to increase the voice call establishment time; at the same time, the data traffic is also transmitted through 4G LTE during the call, and the data rate will be greatly reduced, thus affecting the user experience.

Although a fallback to a 4G network increases call latency a bit, VoLTE provides faster call setup time than CS voice fallback, and this additional delay is acceptable. In fact, the biggest disadvantage of EPS Fallback is that, in addition to reducing the data rate, it will also cause a brief interruption of voice connection due to falling back to 4G, which is easier for users to detect than call setup delay.

VoNR (SA networking) has been mentioned earlier, VoNR refers to the end-to-end voice service carried by 5G NR, 5G Core and IMS. Strictly speaking, NR is only the wireless access network part of 5G network, while 5GS (5G System) contains 5G NR and 5G Core, so it is more accurate to call VoNR Vo5G (Voice over 5GS). However, what we usually mean by VoNR is Vo5G.

The advantages of VoNR (SA networking) over EPS Fallback,VoNR are self-evident: first, there is no need to fall back to VoLTE, and the call setup time is shorter; second, it supports the concurrency of 5G voice and 5G data services, that is, we can make phone calls while surfing the Internet at a high speed.

Considering that when the mobile phone moves to the edge of 5G cell coverage, it will lead to poor VoNR voice quality or even drop calls. In order to ensure the continuity of voice calls, it is necessary to switch the ongoing VoNR calls to 4G VoLTE. Therefore, similar to the SRVCC scheme in 4G era, VoNR scheme also supports smooth handover between VoNR and VoLTE through Inter-RAT handover mechanism.

With the introduction of 5G Core, it is worth noting that with the introduction of 5G Core, the 5G R15 standard does not define the interface between 5G Core and 3G Core, and does not support voice call continuity between 5G and 3G CS, which means that IMS / VoLTE must be supported in R15 networks using VoNR, so that when mobile phone calls move beyond 5G coverage, call continuity can be maintained through 4G VoLTE.

However, in the R16 version of 3GPP, based on the existing 4G to 3G switching standard, 5G SRVCC function is added, that is, voice can be switched to 3G CS domain through 5G SRVCC technology.

What are the benefits of VoNR? User experience and network efficiency from the user's point of view, as mentioned above, although VoNR continues the VoLTE architecture and can no longer achieve revolutionary technological breakthroughs, like VoLTE, VoNR has the advantages of good voice call quality, low connection delay, and 5G high-speed Internet access while talking. For example, theoretically, the MOS value of VoNR is 4.6, and the access delay is only 1.5 to 2 seconds; the MOS value of VoLTE is about 4.1, and the access delay is 2 seconds; and the MOS value of 3G CS voice is 3.7, and the access delay is more than 6 seconds.

VoNR can also greatly improve the security and quality of voice calls and bring users a fully immersive experience that integrates voice with video, tactile, kinesthetic and other senses in the future.

From the point of view of operators, the benefits of evolution to VoNR are mainly in the following aspects.

First, VoNR can accelerate the transfer of traditional old and inefficient 3G CS voice to 4G and 5G, thus improving network efficiency, reducing network operation and maintenance costs, and re-ploughing high-quality low-frequency resources.

Second, VoNR is conducive to supporting new 5G applications. Today, we often mention AR / VR, holography and other 5G applications are inseparable from real-time, high-definition audio and video calls, and with VoNR, we can provide enhanced media to better support these new applications.

Third, it can bring new sources of income to operators. Although operators' traditional voice services facing 2C end have been eroded by OTT voice services, as basic communication services, voice services are still a part of operators' income, and the current 5G data packages are almost tied to voice. More importantly, in the era of digital transformation and Wisdom of everything, voice and video services are extending from the connection between people to the vast market of connection between people and things. In the future, in the 5G 2B or 5G private network market, there will be a large number of scenarios that require real-time, high-quality and stable audio and video communications. These scenarios are powerless for best-effort OTT audio and video, and require VoLTE / VoNR and ViLTE / ViNR certainty guarantee capabilities based on IMS (slicing).

Yes, no matter from the point of view of users or operators, no matter from the current network efficiency improvement or from the future business outlook, VoNR is a technology worth introducing. But in the end, it is important to mention that because VoNR is based on 4G IMS evolution design and relies on VoLTE to ensure voice continuity, it is a basic requirement to introduce VoLTE first, which will be more challenging and urgent for operators who have not yet commercial VoLTE.

This article comes from the official account of Wechat: online excellent mercenary (ID:hr_opt), author: communication

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