As a mobile phone user, hopefully, you frequently find yourself in situations when you are connected to a high-speed data network like 4G LTE, WiFi or 5G NR. When you make voice calls in those situations, depending on your mobile network and the cell phone, you may be using technologies like WiFi calling, VoLTE or VoNR.
VoLTE (Voice over LTE), VoNR (Voice over New Radio), and WiFi calling (Voice over WiFi – VoWiFi) are three IP-based technologies in 4G and 5G mobile networks that enable voice calls and text messages (SMS). VoLTE uses a 4G LTE network, VoNR uses a 5G NR network and WiFi calling uses a WiFi network.
Voice calls have always been an essential part of the cellular services mobile operators offer us. While we have many communication options at our disposal nowadays, including instant text messages, voice messages, SMS, MMS, etc., the importance of voice calls is not likely to subside as people will always need to talk. Voice is one of those features we often take for granted because it has always been available in decent quality in most locations. However, the way voice calling happens in a mobile network has changed dramatically over the last decade. VoLTE, VoNR and WiFi calling are the key technological developments that enable highly secure and reliable voice calls in 4G and 5G networks.
WiFi calling vs VoNR vs VoLTE
WiFi calling or Voice over WiFi (VoWiFi) is an IP technology that requires your mobile phone to connect to a local WiFi network to establish a connection with a mobile network entity, ePDG (Evolved Packet Data Gateway). ePDG works with the mobile core network and IMS to ensure secure communication.
VoNR stands for Voice over New Radio (NR), and it is a packet-switched IP technology that requires your mobile phone to be connected to a 5G radio base station – gNodeB. VoNR requires a 5G mobile core network that can work with another network entity IP Multimedia Subsystem (IMS).
VoLTE stands for Voice over LTE, and it is a packet-switched IP technology that requires your mobile phone to be connected to a 4G radio base station – eNodeB. VoLTE requires the 4G LTE mobile core network (Evolved Packet Core – EPC) to work with another network entity IP Multimedia Subsystem (IMS).
If your mobile operator does not have the IMS, then you are not likely to get VoLTE service on your phone. However, in order to get VoLTE on your phone, your mobile phone must support it also. While VoLTE is a 4G technology, you can also get it on a 5G network if your mobile operator is using a 4G mobile core network (EPC) for their 5G network deployment.
Voice over LTE (VoLTE) requires a 4G core network
VoLTE or Voice over LTE (Long Term Evolution) is the voice calling capability in fourth-generation (4G) LTE networks. Before 4G LTE, the 2G and 3G mobile networks relied on conventional circuit-switched technology to enable voice calls and text messages (SMS). The circuit-switched technology is not the most efficient as it establishes a dedicated connection between the mobile network and the phone for the entire call duration. The aim of 4G LTE is to transfer all cellular services, including voice calls and texts, to IP, which requires the packet-switched capability. Even though both 2G and 3G networks have a packet-switched capability for data, the voice and text services are not delivered on packet-switched because it is impossible to ensure service quality. 4G networks do not have a circuit-switched part, and in line with this all-IP vision, they introduced Voice over LTE, an IP calling and messaging service based on the packet-switched technology. LTE networks, however, have a 2G/3G circuit-switched backup option called the circuit-switched fallback (CSFB). At its simplest, CSFB allows a mobile phone to switch to the 2G or 3G circuit-switched connection for voice calls and SMS if VoLTE capability is not available. In VoLTE, the end-to-end quality of service (QoS) can be ensured for the voice call. The specifications ensure that the minimum bandwidth and codec requirements for voice calls align with those for the legacy circuit-switched networks. For Voice over LTE to function, the 4G mobile core network, Evolved Packet Core (EPC), works with IP Multimedia Subsystem (IMS) to enable rich communications, including voice calls and SMS. If you want to know how to find VoLTE capability on your mobile phone and how to enable/disable it, have a look at our dedicated post on VoLTE with screenshots that can help you.
WiFi calling (VoWiFi) requires support from mobile network
WiFi calling or Voice over WiFi (VoWiFi) is not the same as VoLTE, but it is an inter-related technology. VoWiFi allows any cellular device (e.g. mobile phone) to connect to the 4G LTE network as long as it is connected to the internet. So, for instance, if you are in a geographical area with no cellular coverage, WiFi calling (VoWiFi) can allow you to still make and receive phone calls to landline/mobile/other numbers as long as you have an active internet connection. But in order for that to happen, your mobile network operator and your mobile phone must support the VoWiFi capability. Mobile networks require a new network entity called Evolved Packet Data Gateway (ePDG) as an “adapter” to connect any online cellular device to the 4G LTE network ecosystem. The role of ePDG is to make sure that your cellular devices are connected to the mobile network in a highly secure way as long as you have an internet/WiFi connection. Both VoLTE and VoWiFi require IMS (IP Multimedia Subsystem) that works with the 4G LTE mobile core network to establish the necessary connections for enabling voice/text services.
Voice over NR(VoNR) requires a 5G core network
VoNR stands for Voice over NR (New Radio), and it is also referred to as Voice over 5G (Vo5G). VoNR is the capability in the fifth generation (5G) of mobile networks that facilitates voice calls and text messages over the packet-switched network. Conceptually, both VoNR and VoLTE work in a similar way as they are both IP-based and use the packet-switching technique. 5G NR networks are flexible in many ways, and their deployment models are also adaptable. 5G NR networks can co-exist with 4G LTE, but they can also work as stand-alone 5G mobile networks. In a standalone deployment scenario, 5G networks must be able to deliver all services, including voice, without relying on the 4G networks. For VoNR to work, a mobile network requires a dedicated 5G core network that can work with IP Multimedia Subsystem (IMS) to enable rich communications, including voice calls and SMS. 5G networks have a dedicated 5G core network in a stand-alone deployment scenario, meaning that VoNR calls occur in a stand-alone scenario. In a non-stand-alone deployment scenario, 5G networks utilise the switching capabilities of the 4G core network, the EPC. When EPC is used, 5G networks make and receive calls through the VoLTE capability instead of VoNR. Like VoLTE, VoNR also has an end-to-end QoS (Quality of Service) requirement to ensure service quality for voice calls and SMS.
VoLTE, VoNR and WiFi Calling (VoWiFi – Voice over WiFi) are technologies that enable internet-based (IP-based) voice calls and SMS in 4G and 5G networks without relying on the traditional circuit-switched technology. VoLTE or Voice over LTE is a capability that utilises the packet-switched part of the 4G LTE core network to enable voice calls and SMS in 4G and non-stand-alone (NSA) 5G networks. VoNR or Voice over New Radio (NR) is a capability that uses the packet-switched technology within the 5G core network to enable voice calls in 4G and stand-alone (SA) 5G networks. WiFi calling or Voice over WiFi (VoWiFi) is a technology in 4G and 5G that utilises a cellular network entity, ePDG to enable secure voice calls and SMS over any WiFi network.
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 extra support, especially when preparing for a new job, studying a new topic, or 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 you 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 the product overview and product roadmap.