Voice over Long Term Evolution (VoLTE)

There has been lots of discussion happening around for the efficient use of the voice and the text services at the initial deployment stage of LTE network. The voice and text services in LTE network fail to fulfill user expectation as they are with 2G and 3G networks. In LTE network, the voice calls are supported by PS (Packet Switch) network, where as, in 2G and 3G network, it is supported over Circuit Switch (CS) network.

Operators are well aware that most of the revenue has been driven by voice and text services.

Therefore, at the initial stage, it will become a challenge for the operators to roll out LTE network in the country without optimal use of voice and text services.

Currently, operators can adopt following three solutions to use voice and text services in a best way in LTE network:

• Fallback to 2G or 3G for Voice

The first solution developed at the early stage is fallback to 2G or 3G voice service. It enables mobile devices to fallback to 2G or 3G network for Circuit Switch (CS) services, such as voice and text. The issue for adopting this solution is, the call connectivity time is longer and user experience is not up to the expectation. It also needs huge investment to upgrade the software for network devices.

• Voice over LTE via Generic Access Network (VoLGAN)

The second solution developed to overcome from this situation is VoLGAN. It is a node placed in a LTE network, which enables existing Mobile Switching Centers (MSC) to connect with LTE network through a gateway. To deploy this solution, software enhancements is required for circuit to packet gateways, which already exists for Generic Access Network (GAN). The main drawback for this solution is, when user uses the circuit switch call, the video calls are not supported at the same time.

• Voice over LTE using IP Multimedia Service (VoLTE)

Using this solution, operators can use voice and text services through multimedia features. It follows high standardization and connectivity even if LTE network is not fully accessible. At the same time, user can be facilitated with the circuit switch calls and video calls. User can also use the voice chat and text services simultaneously. Most of the telecom companies are investing time to test VoLTE in LTE network. In future, it will play a major role in LTE network. In 2013, VoLTE will be the focus for many tier 1 telecom companies.

VoLTE provides continuity of Voice calls when a user moves from an LTE coverage area to another, where a fallback to another technology is required. This form of handover will be achieved using Single Radio Voice Call Continuity.

To utilize VoLTE solution, following three interfaces are defined with the conformance of IMS-based specification:

• User Network Interface (UNI)

This interface resides between the user’s equipment and the operator’s network

• Roaming Network Network Interface (R-NNI)

This interface resides between the Home and Visited Network. This interface is used, when the user is not in the home network.

• Interconnect Network Network Interface (I-NNI)

This interface resides between the networks of the two parties making a call.

In my upcoming blogs, I will focus on the following points:

•           Core concept of VoLTE

•           How it’s meeting customer expectations

•           Why it’s better than other two solutions

•           Implementation of VoLTE

•           Positioning of VoLTE in the LTE network

•           Key functions of VoLTE

•           Features to be supported by VoLTE in the upcoming technologies