Voice over LTE
Voice Over LTE aka VoLTE is the next evolution of how mobile/cellular service providers will provide voice services to their customers.
Historically cellular networks were designed and configured from the ground up to support three categories of service. These being voice, SMS/Text and Data. Cellular devices could only operate one of these services at a time. 4G/LTE is a Data only network. Which means for voice or Text to work the device needed to reconnect to 3G to use these services.
Not long after the deployment of 4G/LTE capability the service providers, with advancement of international standards and availability of hardware/software, were able to configure their networks to operate both SMS/Text and Data services on their LTE/4G networks. This removed the requirement for the device to fall back to 3G to make or receive a text. Voice calls still require the device to reconnect to 3G before a call is made or received.
The latest enhancement of capability is to enable voice calling over the LTE/4G network, aka VoLTE. Voice calling on cellular networks has now become another data service just like voice calling became a data service on fixed networks known as Voice over IP, VoIP. Both VoLTE and VoIP have required enhancements in quality of service capability over IP data networks as well as major changes to the base infrastructure to enable these services compared to legacy voice networks.
All of the NZ mobile service providers have rolled out VoLTE to their customers. The marketing departments would have you believe that VoLTE will enable;
Better sound quality
Quicker call connection
Longer battery life
All of these things are sort of true. The better sound quality is with advancements in audio codecs. The existing 3G wideband adaptive multi rate (WB-AMR) audio codec with a data rate up to 23kbps samples audio signals up to 7KHz. VoLTE supports WB-AMR as well as the latest cellular codec known as Enhanced Voice Services (EVS) which has data rates up to 128kbps and sampling of audio signals over 14KHz. Both 3G and 4G are backward compatible previous cellular codecs remembering that both devices in a voice call need to be operating at the same codec to achieve the advanced codec benefits.
What you might not appreciate is that before you can roam onto another network your home telco and the foreign telco will have configured and tested the technical parameters and signed commercial agreements with each other.
The quicker call connection advantage and the better battery life are simply that your 4G device does not need to drop back to 3G before you can make/receive a voice call.
Despite the customer experience advantages there are economic reasons why the mobile service providers are keen to move customers off 3G and onto 4G for voice calling. The first economic driver is that the infrastructure that supports voice calling was deployed or refreshed when they rolled out 3G in 2008/2009. 10 years is a very long time for cellular infrastructure and so their preference is to replace existing voice infrastructure to evolve to VoLTE. The second economic driver is that as more customers use VoLTE this results in less capacity required in 3G to support voice and thus the spectrum currently used for 3G can be reused for 4G and in some cases 5G. Efficient use of spectrum is vital for mobile service providers.
Device support for VoLTE is still emerging with most top end and mid range devices available for sale now supporting it. All three of the NZ cellular service providers have rolled out VoLTE.
For customers there are service experience advantages with the improved call clarity and potential improved battery life for standard voice calling. The evolution of the mobile service providers to VoLTE will be invisible for mission critical services.