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Voice over Long Term Evolution (VoLTE)

January 16, 2018
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Rapid increase in data traffic over cellular network is necessitating deployment of Long Term Evolution (LTE) in the cellular operator’s networks. While LTE provides efficient data traffic handling and high data rates, it lacks native circuit switched voice capability. Mobile operators have begun migrating to fourth-generation (4G) architectures based on the Long-Term Evolution (LTE) standard, including the Evolved Packet Core (EPC) architecture defined by the 3rd Generation Partnership Project (3GPP). According to a recent report from the Global mobile Supplies Association (GSA), LTE has become the fastest-developing mobile communications systems technology.

What is Voice over Long Term Evolution (VoLTE)?

The data traffic, in telecom system, is growing at a rapid pace. However, presently for any mobile system to be commercially viable, the ability to carry voice traffic is essential. The existing 2G/3G mobile systems use “Circuit Switching” to carry voice traffic. In Circuit Switching a dedicated, end-to-end, channel or circuit is established to carry the voice traffic for the entire duration of a transmission. On the other hand, in case of IP networks, the voice traffic is carried using IP packets over data connection. For this generally “VoIP” or “VoLTE” solutions are used.

For mobile communications service providers (CSPs), Voice over Long Term Evolution (VoLTE) has emerged as the preferred solution for enabling real time voice traffic in the emerging world of all-IP networks. When this transition is complete, the circuit-switched network for voice communications (in which a dedicated circuit path is reserved for each call) will be replaced by an all-IP network in which flow-based QoS informs network resources of quality requirements to ensure call quality.

Voice over Long Term Evolution (Voice over LTE or VoLTE) is the practice of packetizing voice over the Internet Protocol (VoIP) and transporting both the signaling and media components over a 4G LTE packet switched (PS) data path. This is in contrast to delivering voice using circuit switch (CS) methodologies, which requires 4G handsets to employ a secondary 3G radio and network operators to continue supporting this inefficient access infrastructure and licensed spectrum.

Long Term Evolution (LTE) network technology is considered as an IP network. LTE operates on packet switched network technology, and hence voice is not supported. But voice calls must be provided to customers on packet switched LTE network. In order to perform this, VoLTE was introduced. It is a technology which provides voice and Short message service (SMS) on LTE.

Long Term Evolution (LTE) and its true fourth generation manifestation, Long Term Evolution-Advanced (LTE-A), are technologies that operators are deploying, or planning to deploy, to help them tide over this evolutionary trend.

LTE Architecture

With LTE a move has been made towards a complete IP network consisting of the Evolved Packet Core (EPC), the Radio Access Network (RAN) and the interconnection. With LTE a move has been made towards a complete IP network consisting of the Evolved Packet Core (EPC), the Radio Access Network (RAN) and the interconnection. Figure 1 shows the broad architecture of LTE.

LTE Architecture

Figure 1: LTE Architecture

The User Equipment (UE) includes functionalities of a Mobile Terminal (MT) that is responsible for call functions, a Terminal Equipment (TE) for data streams and Universal Subscriber Identity Module (USIM). The USIM stores network identity and user information.

The Radio Access Network (RAN) part of the LTE is called the Evolved UMTS Radio Access Network (E-UTRAN). It handles communication between the UE and the Evolved Packet Core (EPC) and consists of the base stations called eNodeBs (eNBs).

The Evolved Packet Core (EPC) or System Architecture Evolution (SAE) is the new all-IP core defined by 3GPP in Release 8. It performs, among others, network access control, mobility management, security and network management functions. The subscriber information is stored in the Home Subscriber Server (HSS). The mobility management entity (MME) controls the set-up and release of connections between the user and the packet data network.

Benefits of Voice over Long Term Evolution (VoLTE)

The implementation of VoLTE offers many benefits, both in terms of cost and operation. VoLTE:

  • Provides a more efficient use of spectrum than traditional voice;
  • Meets the rising demand for richer, more reliable services;
  • Eliminates the need to have voice on one network and data on another;
  • Unlocks new revenue potential, utilizing IMS as the common service platform;
  • Can be deployed in parallel with video calls over LTE and RCS multimedia services, including video share, multimedia messaging, chat and file transfer;
  • Ensures that video services are fully interoperable across the operator community, just as voice services are, as demand for video calls grows;
  • Increases handset battery life by 40 per cent (compared with VoIP);
  • Delivers an unusually clear calling experience; and
  • Provides rapid call establishment time


[1] Lav Gupta, “Voice over LTE: Status and Migration Trends”, available online at:

[2] Wasi Ahmad DDG and Laxmi Dir, “Voice over LTE: New Voice Dynamics”, Telecom Engineering Centre Khurshid Lal Bhavan, Janpath, New Delhi – 110011.

[3] Navin Dhinnesh ADC, “Voice Over Long Term Evolution Call Flow”, International Journal for Research in Emerging Science And Technology, Volume-4, Issue-12, Dec-2017

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