5G is ON.
2019 is the year for 5G commercialization, a year where leading operators are beefing up 5G deployment to quickly launch higher-speed 5G data services (though 5G offers much more than that), and attract more users. Voice services, one of the fundamental services for operators, also raise worldwide operator concern about its development and evolution in the era of 5G, the connection between Voice over LTE (VoLTE) and Voice over 5G (Vo5G), and voice network evolution towards future.
IMS-based 5G Voice Services
5G will continue to utilize 4G voice architecture and the IP multimedia subsystem (IMS) to provide voice services. For 4G wireless access we have LTE networks, and its voice service VoLTE. The 5G equivalent to LTE is NR, and its voice service equivalent is Voice over NR (VoNR).
3GPP has defined how voice solutions will be implemented in 5G networks (as previously mentioned) after the release of specifications for the Non-Standalone (NSA) architecture in December 2017, and the standalone (SA) architecture in June 2018.
In July 2018, Huawei released the Vo5G Technical White Paper. This white paper sets the definition for Vo5G, and describes its key technologies. The white paper also defines a path for evolution towards VoNR and gives suggestions for its implementation, such as deployment of IMS to accelerate subscriber migration to VoLTE networks.
VoLTE is a Must for Vo5G
In a technological sense, 5G era voice services will exist in three forms: IMS voice through 5GC, IMS voice through EPC, and CS voice through MSC. To look at it in this way is too simple and does not mean much.
So by changing the perspective and looking at it in terms of carrier deployment and the voice experience of users, we can better understand how to select voice solutions for different stages of 5G.
- 5G NSA phase: It is foreseeable that most operators will start by launching 5G services in NSA mode. Before launching 5G services, these operators will provide voice services for 4G subscribers through CSFB or VoLTE, while still maintaining voice services for 2G or 3G subscribers through the CS network. When 5G services are launched, operators should, by default, enable VoLTE services for 5G NSA subscribers. Otherwise, users will need to fall back to the 3G network when making and answering calls. This fallback would decrease the bandwidth from 5G to 3G speeds (up to a 100x decrease), and it would also mean an increased time to establish a call. In this case, users wouldn't really be able to fully experience the outstanding experience that can be provided by 5G, and instead would see a degraded version. This would be despite their willingness to pay for better 5G, and despite them switching to a 5G capable terminal and mobile plan.
- 5G SA initial phase: If 5G NSA subscribers do not subscribe to VoLTE services, they will experience the "degraded" 5G experience. If a 5G SA subscriber does not subscribe to the VoLTE service in the 5G SA phase, the subscriber cannot initiate or receive voice calls. This is unacceptable. As defined in 3GPP R-15, CS fallback from 5G to 2G/3G is not supported. This means that when a voice call is set up, 5G SA networks should use Evolved Packet System Fallback (EPS FB) technology for voice fallback to the LTE network, completing the connection through VoLTE.
- 5G SA mature phase: NR coverage will be more comprehensive in this phase than in the initial phase, but it will not have reached full coverage. The industry, especially in the case of terminals, will need to mature. Terminal support for 5G SA will need to become mainstream, and their default configuration will need to be for VoNR (set to ON by default), the then main provider of voice services. When the user moves outside of 5G coverage during a call, Packet Switched Handover (PSHO) technology can be used to seamlessly switch the session from the NR to the LTE, leaving VoLTE to take over voice services. (This is similar to the Single Radio Voice Call Continuity (SRVCC) in 4G, but the principles are different.) Because session control on 4G and 5G networks is integrated into the IMS for processing, a complex cross-system (like from 4G to 2G/3G) SRVCC handover procedure can be avoided. A simple PSHO is performed only in the access domain to switch the transport, preventing the upper control layer from perceiving it. Therefore, VoLTE should be constructed as a fundamental, ubiquitous network with full coverage in this phase, so that the 2G/3G network can be retired to save operation costs and unlock spectrum resources.
To sum up, VoLTE is mandatory for 5G deployment and development. It is imperative that operators increase VoLTE investment, not just for network deployment, but also to accelerate subscriber migration to VoLTE.
Accelerating Voice Migration to VoLTE for Network and Spectrum Efficiency
The VoLTE industry has already matured. There are more than 1.2 billion VoLTE subscribers, on more than 170 worldwide commercial networks, and more than 2000 VoLTE terminals.
The optimal path for operators to increase the value of VoLTE is to simplify the network and coordinate spectrum resources. The 2G/3G network is to be gradually retired from the network (including the wireless network and core network) to reduce OPEX and simplify the network. As more and more subscribers are migrated to VoLTE networks, spectrum resources (especially scarce, valuable low-frequency spectrum resources) used for CS voice services will be released and refarmed for new services such as LTE or NB-IoT, improving spectral efficiency.
Although the VoLTE industry is mature and operators know the value of VoLTE, it is not easy to migrate such a large number of subscribers from the CS network to the VoLTE network. More than 170 operators have deployed commercial VoLTE services, and some of them have been in commercial use for at least two years. However, there is not enough subscriber uptake. Most complaints lead to the fact that there are too few terminals supporting VoLTE on these networks. They have reason to complain.
Although more than 2000 VoLTE terminals (hardware support) have been deployed, not all of these terminals can be used on any VoLTE commercial network. In addition, terminal vendors need to provide software versions that correspond to the target VoLTE network. Although the hardware of older models supports VoLTE, terminal vendors usually only provide this software for their newer models. This requires more cooperation and negotiation between operators and terminal vendors.
In addition to the challenges from terminals, LTE coverage is insufficient and VoLTE services are difficult to provision precisely. This is a major factor in the less than rapid development of VoLTE users. However, the most important factor in solving these challenges, lays mostly in the hands of operators, and their determination to develop VoLTE capable networks.
Operators need to treat VoLTE as a strategic service for the development of 5G rather than an alternative to common voice services, bring about large-scale network simplification, reintegrate spectrum resources, coordinate high quality resources (both budget and manpower), optimize networks, introduce new terminals, and provision new services. This process has been shown and verified by many operators as a sure fire way to promote fast development of VoLTE subscribers.
Evolving to a 'Single Voice Core' in the Next Five Years to Reduce OPEX
In preparation for 5G, operators should increase their investment in VoLTE, build VoLTE into a ubiquitous, fundamental voice network, accelerate user migration to VoLTE, and simplify network and spectrum integration.
With the introduction of 5G voice services, voice network assets gradually accumulate, bringing higher OPEX to operators. In addition to the IMS-VoLTE and Vo5G voice networks, CS voice networks will coexist with VoLTE for a long time. For operators looking to provide comprehensive voice services, there are three more fixed networks: PSTN, NGN, and IMS-VoBB. The coexistence of five voice networks brings the following challenges: added maintenance and management of multiple generations of hardware equipment (especially EOX management), costs from scattered equipment rooms, and labor costs for maintaining management of multiple networks. It is time to take action for the long term, to restructure and optimize existing voice assets.
As a solution, Huawei proposes the "Single Voice Core" solution alongside auxiliary solutions to help operators simplify their five voice networks into one, and reduce OPEX.
"Single Voice Core" uses a combination of "full cloudification" and "full convergence" to simplify the voice network, integrating all voice connections into IMS, reducing OPEX, and accelerating the rollout of new services.
- Full cloudification: Huawei provides a full range of "All-cloud" E2E voice solutions and product combinations with high reliability and flexibility. Among these is the industry's first cloud-based media plane product CloudSE2980. This product moves media to the cloud all at once, preventing replacement of the media plane that might happen with a traditional platform (for example, EOX replacement of MGW products.) Replacement of this platform with a cloud-based platform is a must for the future. As voice network assets are gradually moved to unified cloud-based hardware, OPEX will reduce significantly.
- Full convergence: More converged products can undoubtedly bring a simplified network architecture. Huawei provides converged products on the voice control plane, gateway exchange, and media plane. The functions of multiple NEs can be provided with just one converged product. This helps operators reduce the switch nodes on the network, reduces reliance on IT integration interfaces for bringing new services online, and reduces the manpower required for O&M, thereby bringing faster service rollout and lowered operation costs.
5G voice will still utilize the IMS architecture of the 4G VoLTE voice network, so Huawei suggests that operators pay attention to the following:
- As is, the 4G VoLTE voice network should be deployed as a fundamental network for voice services that covers the entire network to accelerate the migration of subscribers to the VoLTE network and prepare for the smooth evolution to Vo5G. Huawei's VoLTE solution has been commercially launched by more than 60 operators worldwide, serving more than 400 million users. Leveraging mature solutions and extensive experience in implementations, Huawei is able to help operators quickly deploy and commercialize VoLTE networks, ramp up subscriber migration to VoLTE, and smoothly evolve to Vo5G.
- In the long run, simplification of the voice network and reduced OPEX will come with the evolution of the voice network to a full-cloud, and fully converged voice network — "Single Voice Core". Huawei provides a full range of end-to-end product portfolios for Single Voice Core evolution, and is committed to working with operators to optimize voice assets and evolve towards the future.
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