Ever since we started our journey with cell phones, voice calling has clearly 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 without bragging too much about it. There may have been some buzzwords like carrier-grade voice and HD voice, but the fact remains that voice has always been there. If ‘voice’ is such a basic part of mobile phone service, why is it that the telecom world had to make a thing about ‘voice’ over LTE or VoLTE 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. You may wonder what LTE has to do with that and why it is such a big deal as we have been using services like Skype, WhatsApp, Face Messengers, etc. on WiFi for years. That is what we will cover in this post to find out why VoLTE and VoWiFi are not just some marketing buzzwords but a comprehensive set of technologies that provide a secure way to offer high-quality voice services.
What does VoLTE stand for?
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 phones calls instead of using the conventional voice calling technologies that exist in the 2G and 3G networks. The conventional voice calling in mobile communications utilises a specific technology called CS, short for circuit-switching. The mobile internet in mobile networks is enabled by another technology PS short for packet-switching. When you are making a normal phone call, for example, in the UK, 0118xxxxxxx, the mobile network needs to communicate with external networks like local landline (PSTN) or local mobile (PLMN) networks to initiate and complete the call. This capability requires the mobile network to be integrated with PSTN which is how a phone service provider connects your call to other landline or mobile phone numbers. Of course, this is not the case when you are making an internet-based call using an online app such as WhatsApp, but when you are in a situation where you need to dial a number through an internet-based phone, PSTN connectivity is requried. 4G LTE networks use something called IMS (IP Multimedia Subsystem) that connects these IP-based calls to other external networks like PSTN and ISDN. You can find details about CS and PS in this dedicated post.
Is VoLTE the same as WiFi calling?
WiFi calling is not the same service as Voice over LTE, but they both use a similar network architecture for making voice calls over the internet. VoLTE uses mobile data to connect to the internet and then uses the mobile operator’s 4G network infrastructure to connect to external networks such as PSTN, ISDN etc. WiFi-calling (VoWiFi or Voice over WiFi) on the other hand allows callers to make and receive phone calls when they are not connected to the mobile 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. There are several ways in which a mobile operator can deploy WiFi calling; here is a link to a page from Huawei that explains it really well. Generally, the 4G LTE core network (EPC – Evolved Packet Core) and IP Multimedia Subsystem (IMS) are the key network entities that enable WiFi calling just like they do for Voice over LTE, but there is one additional entity involved called ePDG – Evolved Packet Data Gateway. ePDG has a special capability to connect a mobile network to any internet-connected devices even if they don’t have a SIM card. ePDG does this by connecting the core part of the 4G network (Evolved Packet Core – EPC) to any non-mobile (i.e. not part of cellular / 3GPP) devices as long as they are connected to the internet. This way, any internet-connected devices can benefit from the 4G core network and IMS just like any VoLTE connected devices can.
Are VoLTE calls free?
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 together with the mobile core network takes 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. The business and pricing model for each operator is different so you should always speak to your mobile operator before relying on WiFi or VoLTE calls especially when travelling abroad to avoid any bill shocks.
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 you are 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; have a look at this post for more information 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.