March 4, 2016 | by Wayne Smith

Voice Over LTE (VoLTE)

You may have a very smart phone and be on an LTE network, but your voice calls may be connecting over the 3G GSM/UMTS or CDMA2000 networks. If this is the case, the voice quality isn’t up to 4G quality and it requires your phone to consume twice as much power since it is supporting two networks. Currently most smart phones don’t inherently support voice calls and must connect via a dual-mode to the 3G hybrid circuit-switched/packet data networks. In fact, LTE doesn’t inherently support voice calls without assistance from additional technologies like VoLTE. VoLTE technology is a mobility-enhanced version of Voice-over-IP (VoIP) and is based on the IP Media Subsystem (IMS) network. VoLTE was developed to be totally compliant with both the Internet Protocol (IP) v4 and IPv6.

Dual modality is not only a problem for the user. It is also a problem for the wireless network provider. To connect a call to the older network, it must maintain a lot more equipment, use more energy, use more bandwidth and provide a lower quality service than it would if everything were supported only on the LTE network.

VoLTE Architecture

p>The heart of VoLTE lies in the IP Multimedia Subsystem (IMS), and how this system interacts with the Evolved Packet Core (EPC). We discussed the EPC in an earlier article about LTE, and we will focus on the IMS here. The IMS is the architectural framework for delivering the IP protocol and IP multimedia services. The framework is similar to the EPC in that it has a flat architecture and shares certain EPC components like the Home Subscriber Server (HSS). As in the EPC, the flat architecture can be divided into a control and a user data plane. The user plane basically consists of an application server (AS) that handles voice. The control plane includes a group of functions that manage Session Initiation Protocol (SIP) including session signaling, requests, forwarding and the management of interfaces with other entities throughout the system plus the management of multimedia sessions.



Since the LTE OFDMA access technology has much higher spectral efficiency than legacy networks, a VoLTE implementation has up to three times more voice and data capacity than 3G UMTS and up to six times more than 2G GSM. It also reduces user equipment power consumption when there is no data being transmitted or received. Earlier generation networks consumed data as long as the circuit connection is established. This can result up in to 40% power savings compared to a typical GSM/UMTS 3G phone. In addition, LTE networks support Quality-of-Service scheduling to ensure that voice packets are efficiently transmitted to reduce latency and jitter. In sum, VoLTE provides high quality voice to the mobile user with lower demands on the user device and the network. It is a substantial step forward in the network’s evolution.


All cell phones require a codec to convert audible sound waves into digital data and digital data into sound waves. VoLTE uses an adaptive multi-rate (AMR) codec that is highly efficient and extensively used throughout the industry. A key advantage of this codec is that it is interoperable with most legacy systems, therefore, eliminating the need for a trans-coder to talk with legacy networks.


The combination of LTE and VoLTE is very impressive. Combining these with the additional spectrum from AWS puts a wireless provider in an incredibly competitive position. Look for these services in your neighborhood; you won’t be disappointed.