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Voice over LTE (VoLTE) simplified for the layman

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Since the launch of Jio, one of the technical jargon’s that is widely in buzz is VoLTE and Reliance Jio is also betting big on VoLTE. Being a highly technical terminology there have been many doubts arising on VoLTE. We have tried to clear all those doubts/confusions with this article. I will also try to explain VoLTE in a very simple terminology without going much into technical details and keep it as short as possible.


While I will not consider all the aspects/implications of technologies, I will explain mainly about VoLTE in a consumer centric approach. *The disadvantages of any technology discussed here is out of the scope of this article.

Voice/Data implementations in India :

1. GSM/G/GPRS :  Voice call without simultaneous data transfer support
2. EDGE/E :
a) Voice call without simultaneous data transfer support
b) Voice call with simultaneous data transfer support – Some operators have implemented this technology as well in India.
3. 3G/H/H+ : Supports both voice and data sessions simultaneously. So, even when you are active on a call you can still be able to download, send an email or respond to a whatsapp message. Networks are upgraded and now support HD Voice calling as well.
4. LTE : Initial technology LTE (Long Term Evolution) was designed and developed to support great speeds which lacked support for voice calls. There comes this barrier of dependency to fallback on previous version of technology (3G) to make a voice call. The designers of technology felt a need to put an end to this drawback and developed VoLTE technology which means Voice over LTE with many other improvements as well. The developers of this technology embedded voice as an added preference to the existing LTE, where voice was given extra preference and hence VoLTE

a) LTE with CSFB – The technology which rest of the operators have deployed : LTE without voice add-on but CSFB
b)VoLTE – The technology which Jio has deployed : LTE with voice add-on

Now that we have VoLTE, it doesn’t need any other legacy network (3G) to depend on for voice calls. Any operator can directly implement this technology without the need to deploy any other technology to rely on for voice and data simultaneously. Hence Jio has only deployed this technology on their networks and don’t support 3G/2G. To experience VoLTE one needs to have a supported device along with network, otherwise all the calls going through LTE network will be treated just like any other VoIP call like those made on OTT players.

VoLTE enabled network is a complete data oriented network unlike legacy networks. Hence voice in VoLTE will also be transmitted over data but will not be considered as the normal data which we are using for browsing/downloading or any other internet activity. Hence the network is built to have a separate priority for voice packets, which is a technical specification itself. As voice packet becomes prioritized over a data packet, VoLTE will enable a rich multimedia voice experience, providing an edge to operators against OTT players which differentiates between voice call on VoLTE from a VoIP call on LTE by OTT players.

How Voice is prioritized in VoLTE:

VoLTE relies on the IP Multimedia Subsystem (IMS) network.When the connection bearer has been established (Voice call in layman terminology), the VoIP packets which are sent using Real-time Transport Protocol (RTP) are down sized using Robust Header Compression (RoHC) and are transported using Radio Link Control (RLC) Unacknowledged Mode (UM) to minimize packet size and thus increase coverage and capacity which is better than 2G or CSFB networks.

Example :

If we compare the voice over LTE (VoLTE) to an ambulance on a road along with other vehicles  (OTT VoIP players), just like an ambulance enjoys extra privileges on roads compared to other vehicles, VoLTE enjoys extra privileges due to prioritization in network layer as opposed to VoIP by OTT applications where voice is treated with a different priority in data layer. OTT applications have no integration with network layer and just use DATA as they communicate using that layer utilizing the packets. Since voice is integrated into network in VoLTE , it gets more preference and enjoys the advanced benefits. But overall, VoIP and voice in VoLTE almost use the same technology under the hood.

Charging and Qos :

A process in IMS domain, takes care of the Qos and charging rule analysis for the data used by voice of VoLTE which results in a guaranteed bit-rate for VoIP media and also helps to zero out any data volume charging on this data. Hence an individual doesn’t need an active data connection to make VoLTE calls (as there will always be an active service listening to take up calls independently on network) and data used by the voice call will not be charged from the main data balance of an individual. Again as operators can count the data/time consumed by the voice call on VoLTE it is up to their discretion to levy charges on the calls or not. Hence traditional Voice over VoLTE has nothing to do with net neutrality violations or packs.

Also read: What is the difference between G, E, 3G, H, H+ and 4G symbols? We find out!

Some notable points:

1.  High Definition (HD) Voice comes as default with VoLTE. AMR-WB, used for HD voice in VoLTE is the same voice codec used in HD voice on 3G Networks as well.
2. VoLTE works best with lower frequency bands which can be used for LTE.
3. Jio join app is just another OTT application; a turnaround to support calls on non VoLTE devices.
4. VoLTE calls enjoy less power and data compared to the voice service from OTT players in a network perspective.
5. Amdocs Network Research: VoLTE Call Drops Are 4-5 Times Higher Than 2G/3G Calls

Dear readers, hope I was able to clarify all the doubts that many of you might be having on VoLTE. Do let me know your thoughts via comments or tweet me @Srikapardhi .

*Note : Views expressed are author’s own. Some actual technical scenarios or terms are changed/modified to be best understood by any reader. Terminology used here to explain to an end user may or may not be the best suited explanation considering actual technical specifications. 

This post was last modified on September 7, 2016 8:24 pm


Passionately following the Indian #Telecom Industry for over a decade from Business, Consumer and a Technical perspective. My primary focus area is Consumer & Digital Experience.

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