Voice is the most fundamental and an essential service when it comes to mobile communication. In 2G and 3G, voice was a primary network service and was mainly handled in circuit-switched fashion. It was only until the network architecture was changed to all-IP in 4G, an alternative solution was needed to replace traditional circuit-switched voice calls with packet-switched fashion which could deliver more sophisticated IP-based voice service. This is how Voice over LTE (VoLTE) was emerged. VoLTE offered superior call quality with a significantly reduced connection delay. However, most 4G networks had chosen an option of CSFB (Circuit Switched Fall Back) to hand over voice calls to legacy networks (2G/3G) on the fly. Most of the operators went with the CSFB approach, skipping a much more sensible approach of VoLTE entirely. Hence, the adoption of IMS has been slower. According to data, VoLTE adoption in UK is around 60%. This is more or less the same with all operators across the globe. In contrast, India’s Jio has all-IP LTE network with 100% VoLTE adoption. There is another standard called Voice over Wi-Fi (VoWiFi, or simply Wi-Fi calling) that allows offloading of the VoLTE traffic to any Wi-Fi/WLAN network, thus ensuring the superior call quality even in areas where network coverage is low.
Using IMS for enabling packet-switched mobile voice
First introduced back in 2003 in 3GPP Release 5, IMS (IP Multimedia System) is an architectural framework that delivers multimedia services over a packet-switched network. IMS is the backbone of VoLTE and VoWiFi. It uses SIP (Session Initiation Protocol) as a signaling protocol for the initiation, maintenance and termination of real-time call sessions. It can offer various services such as voice calls, video calls and SMS messaging. Even though 3GPP had put an end to the circuit-switched era in Release 15 (5Gv1) mandating operators to use IMS for 5G voice, the legacy alternative was re-introduced in Release 16 (5Gv2). Irrespectively, operators should be opting for end-to-end packet-switched voice on their most advanced 5G infrastructures (With great power comes the great responsibility!)
Voice over 5G (Vo5G) aka Voice over NR (VoNR) will need some evolutionary upgrade over existing IMS implementation (if any). This upgrade is a must in order to support the new interfaces within the Service Based Architecture (SBA) of 5G. The enhanced IMS must be cloud-native, and thus utilizing containerized OS-level virtualization leveraging numerous benefits such as auto-scaling, improved security and faster deployment. This cloud-native IMS also provides numerous 5G-specific benefits such as network slicing. A dedicated network slice for IMS will effectively isolate the 5G voice from the rest of the data traffic, enabling highly reliable and optimized voice experience.
There is a makeshift solution called EPS fallback. In case the IMS and/or the core network is not upgraded to 5G by the operator, EPS fallback allows to make the voice call over VoLTE when connected to 5G. The same approach is being used by most of the current 5G operators operating non-standalone (NSA) mode.
Readiness of the market for Vo5G
Chipmakers like Qualcomm and Mediatek have introduced chipsets with native support of VoNR, with Mediatek’s Demensity 1000 chip and Qualcomm’s third generation Snapdragon X60 modem. Phone manufacturer Oppo supports 5G voice calls with the latest smartphone Reno 3. While the availability of VoNR is currently limited to a few ones among current 5G enabled smartphones, we can expect more and more devices in 2021. Most of the current 5G phones and network operators use EPS fallback for making voice calls over 5G. Talking about the equipment vendor’s contribution to 5G voice, Ericsson has put forward some pretty interesting use cases of 5G voice calls like interactive calling.
Although there is much work to be done to enable this next-gen voice technology – 5G, in its nature, opens a huge platform unleashing a bunch of possibilities for innovation and new monetization opportunities for carrier voice (and video) calls.