Is VoLTE (Voice over LTE) in 4G based on VoIP technology?

When mobile networks started their journey, voice calls were the bread and butter for mobile operators. Back then, the only way to deliver voice calls was through dedicated circuits or connections that required circuit-switched technology. As the digital era of mobile communications started in the early 1990s with GSM and D-AMPS networks, the circuit-switched capability (CS), was enabled by the TDMA technology (Time Division Multiple Access). The 3G networks including, UMTS and CDMA2000 were based on the CDMA technology (Code Division Multiple Access) and they continued using the circuit-switched capability for voice calls. However, as data networks especially the internet became more widespread, things started to move toward packet-switched capability. In packet-switched networks, all services are delivered in the form of data packets without requiring a dedicated connection for each user. VoLTE and VoIP are two closely interrelated concepts in the telecom industry that require packet-switched capability. This post aims to outline what VoIP and VoLTE mean and what relationship they have with each other.

VoLTE in 4G LTE networks is an IP (Internet Protocol) technology and therefore based on VoIP (Voice over IP). As part of VoIP, VoLTE uses the SIP protocol to enable voice calls in 4G networks. Unlike OTT VoIP (e.g. WhatsApp), VoLTE follows strict QoS specifications to ensure high-quality calls.

VoIP – Voice over IP

VoIP stands for Voice over IP (Internet Protocol), and it is a capability in the telecom networks to deliver voice services over the internet instead of conventional phone lines. In today’s world (2021), when WhatsApp, Facebook Messenger, BOTIM and other calling apps are so prevalent, voice calls over the internet may seem like the norm. However, one essential capability in any telecom network is to allow dialling phone numbers locally and internationally, which these apps do not support by default. Dialling phone numbers requires integration with landline and mobile phone networks like PSTN (Public Switched Telephone Network) and PLMN (Public Land Mobile Network). The advancements in the telecom industry have developed technologies that enable VoIP in fixed and mobile networks to use the internet for transferring voice-carrying data packets. VoIP can either be delivered as an Over The Top (OTT) service or managed service. When any service is provided as an OTT service over the public internet, the delivery is based on best effort without guaranteeing the quality of service. On the other hand, when a service is delivered as a managed service, measures can be taken to provide dedicated connectivity to ensure the quality of service. One of the most popular applications of VoIP is in Unified Communications solutions that provide mobile fixed convergence and rely on VoIP for fixed network calls.

VoLTE is a type of VoIP

VoLTE stands for Voice over LTE (Long Term Evolution), and it is a capability in the 4G cellular networks to deliver voice services over the packet-switched data network. The packet-switched data network works on IP, and therefore VoLTE is a type of VoIP service managed end-to-end by a mobile operator to ensure service quality. The 2G and 3G mobile networks relied on circuit-switched technology to deliver voice calls and text messages. 4G LTE networks do not have the circuit-switched capability. Instead, they use the IP Multimedia Subsystem (IMS) to work alongside the 4G mobile core network (Evolved Packet Core – EPC) to deliver real-time communication services like voice calls and text messages through packets of data. IMS provides the necessary integration with external networks such as landline telephone networks (PSTN) to facilitate voice calls. The idea with VoLTE is to make sure that the voice calls follow the same quality standards that were followed by the legacy circuit-switched networks, 2G GSM and 3G UMTS. The quality standards include channel bandwidth, codecs, header compression and other quality of service metrics. The VoLTE calls are initiated and completed by SIP (Session Initiation Protocol) and follow a similar call flow like most SIP-enabled VoIP services. VoLTE technology works on both versions of IP, including IPv4 and IPv6, and uses Adaptive-Multi-Rate (AMR) codecs like the GSM and UMTS networks. It also uses the RoHC protocol (Robust Header Compression) to compress the data headers. For a mobile user, VoLTE calls require the mobile phone as well as the network to support the capability. As a backup, 4G LTE networks also have a 2G/3G circuit-switched fallback option so that any voice calls or text messages can take place over the 2G/3G network when VoLTE is not available.


VoLTE in 4G LTE networks is based on VoIP technology. VoIP stands for Voice over IP, and it is a technology in telecom networks that can deliver voice calls over the internet either as a dedicated or Over The Top (OTT) service without relying on traditional phone lines. VoLTE stands for Voice over LTE, and it is a capability introduced in the 4G LTE networks to deliver voice calls and text messages over IP through the packet-switched part of the 4G or 5G networks.

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, 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 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.

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