Sony demos VoLTE – telecom-grade VoIP over LTE [video]

A few weeks ago, we highlighted LTE coverage for Xperia smartphones to let you know which devices had LTE support and the regions which generally offered LTE service. Now, we’d like to share with you the next step in the evolution of LTE – making voice calls over LTE, which we’re currently demonstrating at Mobile World Congress. Voice over LTE (VoLTE) gives you telecom-grade voice functionality over IP while keeping the high speed data connection. Read on as Sony connectivity engineers, Daniel Lönnblad and Pär Olsson, share their VoLTE expertise.

Daniel Lönnblad, Research Engineer at Sony.

Pär Olsson, Engineering Manager at Sony.

Hi, we’re Daniel Lönnblad and Pär Olsson, connectivity engineers at Sony, and now is a great time to start talking about the VoLTE, because this week’s Mobile World Congress where we’re cooperating with a number of other vendors to demonstrate VoLTE. At MWC, we are demoing development software with VoLTE functionality running on modified Xperia™ V prototypes in multiple stands – Ericsson, Telefónica, Qualcomm, and others. But first, let’s explore the background of LTE and Voice over LTE.

Background to VoLTE
LTE, or Long Term Evolution, provides higher data transfer rate and capacity and lower latency in the mobile environment through new modulation and all IP network. LTE is defined in global 3GPP standards. As interest in LTE continues to grow, and more operators are starting to carry the services over LTE, we at Sony are already on board with the technology, as you’ll find a number of LTE-supported Xperia™ smartphones available on the market.

The way to make voice calls in today’s network is to move the user back to 3G or 2G when a phone call is made or received, this is called circuit switched fallback (CSFB). The ability to make telecom-grade voice calls over LTE is accomplished by means of an IP Multimedia Subsystem (IMS) network specified in 3GPP. Several operators and vendors have profiled the final solution GSMA VoLTE IR.92 specification, which uses a horisontal control layer that isolates the access network from the service layer to aid in the access of voice applications between devices. This removes the dependency of the legacy circuit-switch network and will long term allow operators to only have packet-switch IP network.

LTE benefits
With LTE, end users benefit from improved data transfer and communications. Operators also benefit from LTE by optimising this network infrastructure to provide high-capacity and high-speed data communications. When operators deploy LTE, they can enhance the voice call experience with HD voice and beyond, also more convenient way to connect services like chat, video and file transfer to the voice call. This gives users superior voice quality during calls and seamless using additional communication methods while talking.

VoLTE vs Skype & Google Talk
Given the benefits of VoLTE – broad bandwidth, low latency, and IP-based – the technology is clearly an evolution for mobile broadband voice services. Similarly, another approach based on the usage of over-the-top (OTT) voice services can also be provided over an LTE network. Examples of OTT voice include Skype and Google Talk, applications that enable voice calling over IP for data tariffs. However, VoLTE is still a better solution compared to OTT voice for several reasons.

First, VoLTE can be transparent to the end users, whereas in an OTT VoIP solution, both sides must use the same application to communicate. With VoLTE, everything is integrated in the default phone app and the network handles the interoperability. It is also the same out of the box experience as voice call today with no configuration effort.

Next, the evolution of VoLTE supports the possibility to upgrade an incoming VoLTE voice call to a video call, or downgrade an incoming video call to a VoLTE audio call. Quality of Service (QoS) is another important differentiator between the two. Since VoLTE is an operator service, it will run with a priority over other best-effort data traffic, always giving the best possible user experience. VoLTE also supports handover to legacy (3G/2G) network without interrupting the phone call when moving out of LTE coverage, defined as single radio voice call continuity (SRVCC).

VoLTE – changing the game in telecom
VoLTE is the next step for voice, as indicated by the growth of LTE networks. But what makes VoLTE such a compelling offering?

It starts with the fact that VoLTE operates as a native application in the device, enabling prioritisation over other data streams to have the ability to deliver uncompromised voice quality even beyond toadies HD voice. Users may need to embrace a new way of calling since VoLTE enables super fast calling and will ring instantly at the other end. For example, at Sony, we’ve been able to achieve a one second call setup time in a live network setup.

The evolution of VoLTE also provides enhanced native voice experiences such as video telephony, which is all IP-based, and gives the possibility to switch between voice and video service in an ongoing call. For operators, VoLTE allows for more competitive offerings, the potential for increased network capacity, and in areas where there is limited or no 2G or 3G voice coverage, operators who have LTE 700-900MHz licenses can still offer in-network voice service.

Finally, as VoLTE evolves and network APIs become available, developers will be able to create their own services without having to develop their own messaging or calling technologies, they can just utilise the services and inter-connectibility provided by LTE networks.

Telefónica first to demo VoLTE handover
One of the pioneers in VoLTE making great progress is Telefónica, a leading telecom operator in Europe and Latin America. They recently demonstrated the first, successful test of transferring voice calls seamless from an LTE network to a 3G mobile network at a lab in Germany.

Last summer, Telefónica Deutschland showed how they did the handover of LTE calls to 3G through Single Radio Voice Call Continuity (SRVCC). This is an LTE functionality that allows a VoIP and IMS call in the LTE packet domain to be moved to a legacy voice domain without breaking up. This pioneering breakthrough paves the way for more efficient networks in the future, along with media-rich commercial services.

And as mentioned in the beginning of this post, at MWC this week, Telefónica is demoing pure VoLTE voice services (LTE to LTE calls) using commercially available Xperia™ V smartphones with modified chipsets and modified software support for VoLTE.

Challenges of implementing VoLTE
Many mobile operators are expanding and migrating mobile networks to LTE in order to manage the data traffic explosion. Within the ecosystem, there are some obvious challenges to delivering the Voice service over LTE networks. From a commercial standpoint, operators must invest in moving the voice service to LTE and ensure it will have the same high service grade as legacy networks.

On a technical level, theVoLTE infrastructure is quite complex, and involves different network and IMS (IP Multimedia Subsystem) vendors, operators, device manufacturers. Extra effort needs to be added to make all handset vendors interoperable since most of the signalling when setting up services are made between handset and not only between handset and mobile network as previously.

But in time, best practices should arise from lessons learned by early adopters, and will make it easier for new implementations, but for now, these challenges exist for VoLTE.


We hope this gives you some valuable insight into voice over LTE. If you’re at MWC, come check out the VoLTE demos at our partner booths (please note that these are strict research demos, not commercial products). And feel free to leave us any comments or questions about VoLTE below, and we’ll get back to you as soon as we can.

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  1. By Rishabh Yadav


    in my phone settings I found “turn off volte provisioned flag” button . which means my phone (xperia c5 ultra dual) is VoLTE enabled. still I can’t find any such option to enable VoLTE.
    Please help me out how to enable it.

  2. By Jay Lee


    Mind the DTMF mixed quality BADLY effects your communications. I have a real story for you; I’m calling one of my banks, they Rep is transferring me to a robot to enter my pin #… I’m entering it, and the robot can’t understand the pin. The robot says to enter again… after 3 tries it gives up. …., and it does not understand your commands due to the line in not DTMF. You must troubleshoot DTMF problems with your VoIP connection through They offer free testing credits. You can find the solution quickly. #VoIP

  3. By Jay Lee


    DTMF mixed quality BADLY affects your communications. I have a real story for you; I’m calling one of my banks, they Rep is transferring me to a robot to enter my pin #…
    I’m entering it, and the robot can’t understand the pin. The robot says to enter again… after 3 tries it gives up.

    …., and it does not understand your commands due to the line in not DTMF.
    You must troubleshoot DTMF problems with your VoIP connection through They offer a free testing credits. You can find the solution quickly. #VoIP

  4. By govind avin


    Sony always remain back
    I m using xperia xa ultra
    I got an update
    But not get volte in feature
    And camera quality is so poor

  5. By Siari Debbarma


    is c5 ultra dual e5563 a volte phone or not? If not will there be any future update to enable volte for mediatek 6752 chipper which comes with Xperia c5 ultra dual model?

  6. By Lulu Winñêr


    How to enable volte on xperia c4 dual tell me plzz
    If it can’t be done please develope an system update including it

  7. By Maya pEruMal


    The cheapest mobile phone are supported Volet below 10,000 around range. BUT Sony mobile phone are coat high why does not support Volet for Sony Xperia M5Dual. Any idea for future support this model on volet service? MY mail for . Reply me sir please

  8. By Gourav Shinde


    Hi I have Sony Xperia c5 ultra duel
    How to enable VOLTE in my phone plz give me solutions 7693909419 miss call me I will call u or msg me

    • By imran wani


      I am using the same phone…have anyone contacted u for the solution of problem…

  9. By Arun Muthu Kumar


    I have xperia z wich support lte, but i can’t place a call

  10. By Sree Lal


    Ma name is sreelal am using Sony xperiw z2 d6503 can u plz help me for volte update to ma device.

  11. By Nonu Khera


    I am using Sony Xperia C3 dual. the website of sony claims that C3 dual supports LTE as it has inbuilt lte moderm but the phone shows no settings for lte network mode. Also the 4-G sim doesn’t work in it.
    Some one told me that LTE has to be un-locked in the device. Is it correct? if yes then how can i un-lock it. Otherwise please tell any procedure by which I can use 4-G sim/Lte on my xperia c-3 dual.

  12. By Masoom Raza


    I’m using c5 ultra dual E5563.
    I don’t know my phone is supported volte or not support
    Please help me how to enable volte