What is VoLTE?

Lazaros Agapidis

Nov 14 2022

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Telephony technologies today are developing at breakneck speeds. These developments have introduced many “Voice over X” type technologies, where “X” signifies a method of transmission, the most important of which is Voice over IP (VoIP). But there are many related methodologies that are proliferating, one of which is Voice over LTE (VoLTE). In this article, I’ll be describing this technology, what its relationship is to VoIP, and how it can be leveraged to benefit your business.

The fast pace of voice technology development

Many years ago, new technologies that emerged in voice would have a lifecycle lasting decades. Technologies like Signaling System Seven (SS7) and ISDN, introduced in the 1970s and 1980s respectively, are still in widespread use today, over 40 years later, even though they are in decline. Conversely, today’s developments in telephony and especially in VoIP have brought about many innovations that are highly advanced but often last for much less than a decade before they are phased out in favor of newer and improved protocols. VoIP involves the packetization of voice, a process that allows voice packets to be transmitted via multiple underlying transmission technologies. This has resulted in many innovations in the transmission of voice, each of which has its particular strengths.

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Voice over X technologies

These innovations include technologies such as Voice over Wi-Fi, Voice over DSL, and Voice over ZigBee, just to name a few. These spiffy-sounding names are also often included in marketing jargon, however, they all essentially employ a form of packetized voice. Many of these are not actually industry standards but are terms used to describe the method of transmission of voice packets.

Voice over LTE (VoLTE)

VoLTE is a voice technology that is part of an ITU-T standard for high-speed communications for mobile phones and other data terminals over LTE networks. The acronym LTE stands for Long-Term Evolution, which is a term used to describe a particular set of cellular network technologies. LTE is also known as 4G, and is replacing or has already replaced 2G/3G mobile networks. According to this standard, VoLTE is based on the premise that voice packets are delivered as data flows within the LTE data channel rather than using more traditional circuit switched voice network technologies that older standards employed. Thus, LTE eliminates the dependency upon and the requirement of any legacy circuit-switched voice network. Stated more simply then, VoLTE converges the previously disparate mobile voice and data network infrastructures of more traditional cellular service into a single packet-based transmission method. So when you use your cell phone, both your data and your voice services take advantage of the same packet-based transmission methods.

Technical Implementation of VoLTE

All telephony services, both conventional as well as VoIP-based, have two parts to any voice call: the bearer portion (which is the part that transmits the actual voice) and the signaling portion. Signaling for VoLTE is achieved using the Session Initiation Protocol (SIP), the de facto standard operated by virtually all VoIP providers today. The bearer portion takes advantage of the data transmission mechanisms of 4G technologies and uses IP at the Network Layer (Layer 3) and the RDP and UDP protocols at the Transport Layer (Layer 4) of the OSI model. For those not as technically savvy, this simply means that VoLTE routes your normal cell phone calls in the very same way as it routes your data, using the same packet-based transmission technology.

VoLTE and VoIP services

At first glance, this seems almost identical to the types of services offered by third-party VoIP providers such as Ooma or Ringcentral. With such services, a smartphone app registers to your cloud-based VoIP service and obtains a new telephone number that you carry around with you. This number can function as a shared line with other telephony devices, such as desk phones or computer applications. It may also seem very similar to web conferencing services that are simply used over a cellular data connection. Nevertheless, there is a distinct difference in that these services are considered over the top (OTT) services, while VoLTE is not.

What is an OTT service?

Over-the-top services are those that leverage a network infrastructure in order for them to function. These services are independent of this infrastructure and exploit it only to communicate with other components needed for their operation, which are typically found in the cloud. Vonage is an example of such a service. You can install their app on your smartphone and over the cellular data network, and connect to the Vonage server on the cloud to use their service. In this scenario, the cellular data network is being used only to establish communication. Such services are considered OTT because they run on top of the cellular data network, but are not actually implemented by the mobile provider. The cellular data network is only responsible for a portion of the transmission and nothing more.

Why is VoLTE not an OTT service?

The reasoning behind VoLTE not being considered as an OTT voice application has more to do with the way the technology is delivered rather than the technology itself. Unlike the services delivered by the VoIP services mentioned above, VoLTE is almost always a service that is inherently supplied by the mobile service provider as an integrated part of their service package. It uses a voice framework that is incorporated into its network infrastructure, providing for, and deriving income from, the specific voice service. In other words, the telephone number provided for you by the actual cellular telephony provider is the only number on your cellphone that can use VoLTE. All additional numbers supplied by third-party services via their smartphone apps and cloud services are strictly OTT services.

What does VoLTE look like?

Ultimately, whether you are using an OTT VoIP service, VoLTE or even an older 2G/3G circuit-switched service, the phone call on a smartphone will function in exactly the same way from the point of view of the caller. In all cases, the caller will use the physical device in the same way, listening to the speaker and speaking into the microphone of the phone. All of the magic, however, takes place in the background, and it is that magic that delivers the advantages of this innovative technology.

Advantages of VoLTE

There are many advantages from the implementation of VoLTE in mobile telephony networks. These include: Reachability and ease of use – VoLTE as a service is provided as an integrated part of the PSTN without the need for credentials to configure, no apps to download and install, and no servers to provision. The mobile device is reachable worldwide from any telephone with an internationally standardized E.164 format telephone number.  Reliability – VoLTE is an integrated service offered by the mobile service provider, and as such, it is almost always the most robust voice service that one can have on a mobile telephony device, providing built-in quality of service mechanisms. Alternatively, OTT services are always a “best-effort” service, just like all other data communication services. Security – VoLTE services, although they use the data infrastructure of the cellular provider, are segregated from traffic that is destined to the open and unsecured Internet. This ensures the security and confidentiality of phone calls made over VoLTE infrastructure.

VoLTE and the future

LTE has been around for several years and is considered by many to have already reached its peak. 5G networks are on the horizon with the first widespread implementations already completed within 2020. The question thus arises, what of VoLTE when 5G becomes the dominant cellular technology? 5G has incorporated into its standard, the next iteration of VoLTE which is called Voice over New Radio (VoNR). This, like its predecessor, is an IP based calling service that employs the 5G network for its source of IP voice processing and routing. VoNR is still a newcomer and will require much maturing to reach the point where it can take over from VoLTE. For this reason, VoLTE will be around for many years and will be backward compatible on most 5G networks. So whenever VoNR is unavailable or not implemented, voice communications will fall back on VoLTE. VoLTE and VoNR are actually implemented into the 5G standard as distinct access modes to the IP network. What this means is that VoNR and VoLTE can coexist on the 5G network, a feature that is vital to both the transition period and backward compatibility of VoLTE-enabled devices.


Cellular data networks are one of the fastest-growing sectors of telecommunications infrastructure and as such will continue to play a vital role in the industry. Convergence of voice services such as VoLTE and VoNR is just one of the many applications for these

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