VoLTE and VoIP are two interrelated technologies that enable voice services over data networks. VoLTE is a vital part of mobile cellular networks, while VoIP is a broader technology that is used in fixed and mobile networks.
Voice over LTE (VoLTE) in 4G mobile networks is a type of Voice over IP (VoIP) technology that employs the SIP protocol and specified QoS levels to deliver high-quality voice calls and text messages (SMS). VoIP is a broader technology that enables IP-based voice services in all phone networks.
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 a dedicated connection that required Circuit-Switched (CS) technology. When the digital era of mobile communications started in the early 1990s, the Time Division Multiple Access (TDMA) technology was adopted by GSM and D-AMPS networks to facilitate voice calls and text messages through dedicated circuits. Later, 3G Universal Mobile Telecommunication System (UMTS) and CDMA2000 networks continued using circuit-switched technology for voice calls and text messages and packet-switched technology for data services (internet). 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.
VoLTE is a VoIP technology with guaranteed service quality
VoLTE is a managed-VoIP service where the 4G core network guarantees the Quality of Service (QoS) when delivering voice calls and text messages (SMS- Short Message Service). Service quality, also known as Quality of Service or QoS, is the main difference between OTT VoIP services and managed-VoIP.
VoLTE stands for Voice over LTE or Voice over Long Term Evolution. LTE is the cellular technology that enables the fourth generation of mobile networks, also known as 4G. The cellular technologies in the 2G and 3G era included a circuit-switched part in the core network for voice calls and text messages (SMS) and a packet-switched part for data services like mobile internet. The new generation of mobile networks, including 4G LTE and 5G NR, do not use the traditional circuits for voice calls and SMS. Instead, they use a data-only approach by delivering all services through packet-switched mobile networks. 4G LTE and 5G NR are packet-switched only and require the mobile core network to work alongside IMS (IP Multimedia Subsystem) to enable VoLTE to deliver real-time voice and messaging services over Internet Protocol (IP). Voice over IP (VoIP) is a broader technology used in all telecom networks, including fixed telephony as well as mobile networks. VoIP services can use multiple protocols, and one of the most popular VoIP protocols is Session IP Protocol – SIP. The VoLTE technology uses this SIP protocol in 4G networks.
There are multiple approaches to offering VoIP services, including Over The Top (OTT) and managed VoIP. When provided as an OTT service, VoIP technology allows voice services to be delivered over the public internet where service quality cannot be guaranteed. On the other hand, managed VoIP is typically provided by the network service provider, who ensures that the network maintains critical service quality parameters when delivering voice calls. VoLTE is a managed-VoIP service where the quality of service parameters and necessary codecs are ensured by the 4G LTE core network, Evolved Packet Core (EPC). VoLTE can deliver both voice calls and text messages and even though it is a 4G technology, it is also used by 5G non-standalone networks (NSA). I have written a dedicated post on VoLTE that explains how it works and its relationship with Wi-Fi calling.
How does VoLTE ensure service quality?
The Voice over LTE (VoLTE) technology requires the 4G LTE core network (Evolved Packet Core – EPC) to work with the IMS (IP Multimedia Subsystem) platform. IMS provides the necessary integration with external phone networks such as Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN) to facilitate voice calls. The idea with VoLTE is to make sure that the voice calls follow the same high-quality standards that are employed by the legacy circuit-switched networks GSM and UMTS in 2G and 3G. These voice quality standards mainly include channel bandwidth, codecs, header compression and other Quality of Service (QoS) metrics.
The VoLTE calls are initiated and completed by the SIP protocol and follow a similar call flow as other SIP-enabled VoIP services. VoLTE technology works on both versions of IP, including IPv4 and IPv6, and uses Adaptive-Multi-Rate (AMR) codecs that GSM and UMTS networks employ. It also uses the RoHC protocol (Robust Header Compression) to compress the data headers and reduce their size for easy transmission. For a mobile user, VoLTE calls require that both the mobile phone and the mobile network support VoLTE capability. As a backup, 4G LTE networks also have a 2G/3G circuit-switched fallback option (CSFB), which allows voice calls and text messages to take place over the 2G/3G network when VoLTE is not available.
VoIP is a broader technology used by all phone networks
Voice over Internet Protocol or Voice over IP (VoIP) is a capability in fixed and mobile telephone networks that delivers voice calls over a data network rather than conventional phone lines. Nowadays, when free calling apps like WhatsApp, Facebook Messenger, IMO, BOTIM, etc., are so common, internet-based calling is essentially taken for granted. However, one essential feature that these apps do not offer is the ability to dial phone numbers. To allow customers to dial phone numbers, a telecom operator requires integration with telephone and mobile phone networks. VoIP is a technology that facilitates voice calls over data networks such as the internet. In VoIP, the voice traffic, like any other data traffic, is carried over a data network (e.g. internet) in voice-carrying data packets.
The key difference between a high-quality VoIP service and a best-effort VoIP service is the use of service quality parameters that ensure that the voice traffic is given priority and the necessary network resources. In best-effort voice services, the quality of service (QoS) cannot be guaranteed because they are offered over the public internet as an OTT (Over The Top) service. The opposite of that is a managed VoIP service where necessary measures are taken to provide dedicated connectivity for voice calls to ensure service quality. The best-effort service route is a choice for the service providers willing to take the risk of offering their services over the public internet, e.g. WhatsApp. Service providers that own a mobile or fixed network can offer managed VoIP services over their network. The VoIP technology is used in Unified Communications Solutions that provide mobile, fixed convergence and rely on VoIP to make and receive fixed/mobile calls.
In summary, Voice over IP is a broader technology that enables voice calls over data networks, e.g. the internet. Voice over LTE (VoLTE) is a VoIP-based technology used by 4G mobile networks. VoIP services can be delivered over the public internet as an OTT (Over The Top) service or a managed-VoIP service. VoLTE is a managed-VoIP service where the 4G mobile network ensures that the necessary service quality parameters and codecs are available to deliver high-quality voice calls and messaging.
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.