What is Voice over LTE – VoLTE?

Voice calling has been one of the key considerations for most of us when buying a mobile phone subscription. It is the most fundamental service that our mobile phones provide us, and as a solution, mobile operators have always been able to offer it. If ‘voice’ is such a basic part of mobile phone service, do you wonder why the mobile operators need to talk about VoLTE as a technology, considering it is just a voice service that happens to be on a 4G LTE network? An inter-related terminology is WiFi calling, known in the telecom world as VoWiFi or Voice over WiFi which is a bit easier to relate to, especially if you use WhatsApp or other online apps to make voice calls. We have been using WhatsApp, Facebook Messenger, Viber and other similar apps on our mobile phones for years, so what makes VoTLE and VoWiFi so special that we have to talk about them? This post explains what VoLTE and VoWiFi mean, are there any additional costs for customers and do we really need these technologies enabled on our phones?

What does VoLTE mean on my phone?

VoLTE stands for Voice over LTE, and it is an IP-based voice calling service introduced by the 4G LTE networks. It uses mobile internet (your data allowance) to make phone calls instead of using the conventional voice calling technologies in the 2G and 3G networks. Conventional voice calling in mobile communications is based on a technology called circuit-switching (CS). However, the mobile data part utilises a different part of the network based on packet-switched technology (PS). When making a normal voice call from your mobile phone, the mobile network needs to communicate with external networks such as the landline network (Public Switched Telephone System – PSTN) or other local mobile networks (Public Land Mobile Network – PLMN). That requires the mobile network to be integrated with PSTN, which is how a mobile network connects your call to other landline or mobile numbers. The normal internet calls, WhatsApp calls, for example, work differently as you don’t have to dial a number. Allowing customers to dial a phone number through the phone requires PSTN integration which is only available in CS networks. With VoLTE, Packet Switched networks can integrate with PSTN. 4G LTE networks use IMS (IP Multimedia Subsystem) to connect these VoLTE and/or VoWiFi calls to other external networks like PSTN and ISDN. IMS is also used by 5G networks for Voice over 5G calls in standalone 5G networks.

Screenshot from an iPhone to give an idea of where to find VoLTE

Is VoLTE better than 4G?

VoLTE – Voice over LTE is a 4G capability, so there is no competition between 4G and VoLTE. VoLTE is part of 4G LTE, and some mobile operators even refer to VoLTE as 4G calling to make the relationship clearer. 4G mobile networks support voice calls in two ways; they can either fall back on 2G and 3G networks for all voice calls or use the VoLTE capability within 4G to enable voice calls on 4G LTE instead of 2G or 3G networks.

How does VoLTE work?

VoLTE is a better option for customers and mobile operators for voice calls. For an operator, it is more efficient because your calls are not engaging any of their circuits, and for you, the call is of better quality. There are two key conditions for VoLTE and WiFi calling to work; first, a device needs to be online, and secondly, it must be connected to the mobile network. The second part is where the real magic happens because then the in-built IMS architecture and the mobile core network take care of all the integrations with PSTN and other networks to enable voice calls through the internet in a secure manner. As soon as a VoLTE or VoWiFi enabled device is connected to the mobile network, the IMS infrastructure replicates what traditional circuit-switched calling would have done but using packets of data instead of circuits. Therefore mobile operators have a cost for enabling the service, which is why the calls are chargeable. Nowadays, mobile operators also have partnerships with fixed network providers for enabling WiFi hotspots on certain mobile tariffs, which comes in handy for VoWiFi calls. Mobile Network Operators also have roaming agreements with mobile operators in other countries so that when customers travel to those countries, the partner networks can enable connectivity for them.

Is VoLTE the same as WiFi calling?

WiFi calling, also known as Voice over WiFi, is not the same as VoLTE, but it is an inter-related technology that allows WiFi-connected cellular devices to become part of a 4G LTE network. For integrating WiFi networks to a mobile network, an entity Evolved Packet Data Gateway (ePDG) is used. ePDG establishes a secure connection with the WiFi connected cellular devices using IPsec. IPsec stands for Internet Protocol Security and is a suite of protocols used for encrypting data packets. This way, ePDG becomes an integral part of the overall 4G mobile core network, the EPC to extend the network coverage by taking advantage of the WiFi networks. Both VoLTE and VoWiFi use the same mobile core network to provide a high-quality audio/video calling experience to customers. As a customer, that means you can make phone calls to landline numbers or other mobile numbers as normal as long as you are connected to a WiFi network. It is a great service for those who live in areas with poor cellular coverage or those who often use underground train services like Tube or Metro.

A short description of Voice over LTE – VoLTE

Is VoLTE good or bad?

VoLTE is the future of voice calling, and it is a step in the right direction. It takes the voice calling forward from conventional circuit based calling to IP-based calling. When LTE networks were launched as part of 3GPP Release 8, the main LTE driver for the customers was a higher data rate than 2G/3G networks. The 2G and 3G mobile networks had two different parts of the network operating within them; one for voice calls and SMS, and the other for all things data. Since moving conventional voice calling to IP was a big step, especially in the beginning when 2G and 3G networks were still more widely available than 4G, LTE networks had an interim technology called circuit-switched fallback (CSFB). CSFB is the capability of LTE networks to use 2G and 3G networks for voice calls and SMS. For example, if you have a 4G phone and a SIM, CSFB allows you to make phone calls as normal, but in the background, it will be using 2G (e.g. GSM) or 3G (e.g. UMTS) networks. What VoLTE does is that it takes away that dependency on 2G and 3G networks so that if you are in an area where you only have 4G or 5G network coverage, you can still make voice calls. And not just that, VoLTE is capable of providing a better and more crisp calling experience and is also more power-efficient than other VoIP services.

Should I keep VoLTE on or off?

You should always check with your mobile operator on their WiFi and/or VoLTE calling rates, as these might differ from country to country or operator to operator. When using VoLTE, you are using mobile data via LTE to connect to the internet, which goes out of your data allowance. In addition, of course, there will be charges for the numbers you dial. To avoid bill shock, you can use spend-cap to take control of any such unforeseen costs; look at our dedicated post on spend cap. If you switch off WiFi calling or VoLTE, you will still be able to use your phone for conventional circuit-switched calling on 2G/3G networks. 4G LTE networks also have a capability called Circuit-Switched Fall Back (CSFB) which makes use of 2G/3G networks to make voice calls if VoLTE is not available.

Does VoLTE cost extra?

Generally, there are no extra charges for VoLTE, and the calling minutes come out of your normal calling allowance. So, for example, if you have 500 calling minutes as part of your monthly allowance, the minutes you use for VoLTE calling will come out of those 500 minutes, just like any non-VoLTE calls. Also, even though VoLTE makes use of the packet-switched part of the network, which is data-only, any data that VoLTE consumes does not come out of your monthly data allowance because mobile operators charge for it as calling minutes and not data. However, you must always check with your mobile operator if you are unclear to avoid any bill shocks. Each operator’s business and pricing model can differ, so you should speak to your mobile operator, especially if you are planning on using any of the services abroad.

How do I get rid of the VoLTE symbol?

Not all phones show a symbol on top of your phone screen when VoLTE is enabled, but it is possible to turn VoLTE off on your phone. If you want to do that, generally, you can find the VoLTE tab by going to “Settings” and then “Mobile Data” or “Mobile Networks” tab. Below are some screenshots and guidance to help you do that some iPhone and some Android phones:

iPhone

To turn off VoLTE on an iPhone, you need to go to Settings->Mobile Data->Mobile Data Options->Voice & Data. That will take you to the tab where you can use a slide button to enable/disable VoLTE.

Step 1 – Go to Mobile Data

Step 2: Mobile Data Options

Step 3: Voice & Data

Android phones:

You are likely to find the VoLTE option on Andriod phones under the “Mobile Networks” tab. An example below for a Samsung phone:

To turn off VoLTE, go to: Settings->Connections->Mobile networks. That will take you to the following tab so you can enable/disable VoLTE:

Go to Settings->Connections->Mobile networks and then slide the VoLTE button to enable/disable.

Conclusion

VoLTE or Voice over LTE is a fourth-generation (4G) technology that enables voice calls and SMS over 4G LTE networks. In the absence of VoLTE, the only way 4G networks can facilitate voice calls is by using a 2G/3G fallback option called Circuit-Switched Fallback (CSFB), which utilises legacy networks (2G/3G) for voice calls. VoLTE is a packet-switched technology enabled by IMS (IP Multimedia Subsystem) in mobile networks. It relies on data packets instead of conventional circuits to make voice calls and send text messages (SMS).

Here are some helpful downloads

Thank you for reading this post, I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need some extra support especially when preparing for a new job, or studying a new topic, or maybe just buying a new phone. Whatever you are trying to do, here are some downloads that can help you:

Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy which explains the network nodes e.g. BTS, MSC, GGSN etc.

Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience which is why I’ve carefully put together a few slides to get you started in no time. So if work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on product overview and product roadmap.

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