VoLTE, as is clear from the name itself, is Voice over LTE / 4G network. It allows users to stay connected with 4G network while making voice calls instead of 3G fall back for voice. If VoLTE is not enabled, mobiles will be connected with 4G network for data usage and whenever a voice call is dialled it will fall back to 3G network. However, in VoLTE, it will stay connected with 4G network and initiate a VoLTE call, which is basically via a SIP embedded client with the same phone dialler of the mobile device.
The voice runs on reserved bandwidth on 4G in addition to your normal data browsing. Also, currently there is no additional data charges for VoLTE calls or none of your mobile data allowance will be deducted for voice calls. VoLTE voice calls will be charged as normal according to your mobile plan or contract with same rates.
What are the advantages of VoLTE?
High Quality Voice: In VoLTE, for the media stream, high quality HD voice codecs are used to carry RTP thus, it increases the voice quality from end to end if the receiver also connected to VoLTE network. Mostly wideband CODECs like AMR-WB is used in VoLTE to carry HD voice.
If the call cross the IMS network then it loses the HD quality due to TDM breakout for 3G, 2G and PSTN connections. So mostly you only experience HD quality on voice calls between VoLTE enabled 4G mobiles, IMS network VoIP phones (Broadband VoIP phones), any IP phones connected to operators IMS network via different technologies.
Short Call Setup Time: When you use VoLTE to place a call, as soon as you dial or select the number from address book and press to make call, immediately the call will be setup and you will hear the ringing tone. In some networks, ringing tone may by different compared to normal calling since it plays from your handset.
Increasing Batter Usage: If you started using VoLTE, your power consumption is optimised to provide better performance thus, battery life will be extended compared to normal mode of operation. Since 3G fall back for voice call is no more and all the voice calls including data usage is using the 4G connection, additional battery consumption is avoided.
By Qualcomm, Voice Evaluation