Voice over Long-Term Evolution (Volte) is a standard for high-speed wireless communication for mobile phones and data terminals. It is based on the IP Multimedia Subsystem (IMS) network, with specific profiles for control and media planes of voice service on LTE defined by GSMA in PRD IR.92. This approach results in the voice service (control and media planes) being delivered as data flows within the LTE data bearer. This means that there is no dependency on (or ultimately, requirement for) the legacy circuit-switched voice network to be maintained. VoLTE has up to three times more voice and data capacity than 3G UMTS and up to six times more than 2G GSM. Furthermore, it frees up bandwidth because VoLTE’s packets headers are smaller than those of unoptimized VoIP/LTE.8
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History
In May 2014, Singtel introduced the world's first commercial "full-featured" VoLTE service in Singapore, only in combination with the Galaxy Note 3, it was subsequently expanded to the other.
In June 2014, KT showcased the world’s first cross-border roaming services based on Voice over LTE. The South Korean operator partnered with China Mobile to develop VoLTE roaming services.
In October 2014, operators based on IMS local breakout architecture with home routing systems.
In November 2014, Verizon and AT&T announced the companies are enabling VoLTE-to-VoLTE connections between their respective customers. VoLTE interoperability between Verizon and AT&T customers began in 2015. Testing and design are being done between both companies using third party networks such as Alcatel-Lucent.
On 11 July 2015, SEATEL Cambodia announced the world's first commercial 100% VoLTE service without 2G/3G in Cambodia.
On 16 September 2015, Telstra announced that it had started enabling VoLTE across its network, including calling to National Broadband Network and business and enterprise services with HD handsets.
On November 30, 2015, Telenor Denmark launched VoLTE for all Samsung Galaxy S6 phones, which has since been followed by additional Samsung and Apple models.
In March 2016, Vodafone Netherlands launched VoLTE support, along with Wi-Fi Calling.
On June 30, 2016, YTL's YES launches 4G LTE service to become Malaysia's FIRST VoLTE service provider.
On September 5, 2016, India's first 4G-only network Jio launched their commercial VoLTE service without 2G/3G based services.
In October 2016, Orange Polska launched commercial VoLTE service in Poland.
In November 2016, T-Mobile (Poland) launched commercial VoLTE service in Poland.
On December 7, 2016, Telenor Denmark launched VoLTE for all phones with VoLTE support.
On March 8, 2017, Cosmote is the first operator that launched VoLTE (and VoWiFi) service in Greece.
Deployment
A list of commercial VoLTE deployments around the world can be found in the main article above.
For planned VoLTE deployments see GSA Evolution to LTE report – VoLTE global status (Page 87ff).
Voice quality
To ensure compatibility, 3GPP demand at least AMR-NB codec (narrow band), but the recommended speech codec for VoLTE is Adaptive Multi-Rate Wideband (AMR-WB), also known as HD Voice. This codec is mandated in 3GPP networks that support 16 kHz sampling.
Fraunhofer IIS has proposed and demonstrated "Full-HD Voice", an implementation of the AAC-ELD (Advanced Audio Coding – Enhanced Low Delay) codec for LTE handsets. Where previous cell phone voice codecs only supported frequencies up to 3.5 kHz and upcoming wideband audio services branded as HD Voice up to 7 kHz, Full-HD Voice supports the entire bandwidth range from 20 Hz to 20 kHz. For end-to-end Full-HD Voice calls to succeed however, both the caller and recipient's handsets as well as networks have to support the feature.