4G network operators are keen to implement VoLTE in order to be able to deliver a high quality voice experience to their subscribers, and to reduce their dependence on fall-back to 3G technology for voice calls. At the same time they want to keep costs down by carrying voice traffic over all-IP networks, and are keen to minimise competition from OTT apps such as WhatsApp and Messenger that are chipping away at their voice revenue.

Despite this, almost 90% of the world’s 4G operators have yet to launch their VoLTE service offering. What is holding them back? One of the reasons is that an LTE network needs to have sufficiently good coverage, and a reasonable number of VoLTE-ready handsets in use, before it is possible to offer the service widely. Another important factor is the need to ensure that VoLTE quality of service (QoS) meets expectations. Industry reports are currently indicating that a much higher proportion of dropped calls is occurring with VoLTE than with 3G, by a staggering factor of up to 500%[1], and they will want to make sure that this doesn’t encourage churn. It is no exaggeration to say that VoLTE service development is one of the most difficult challenges mobile operators can expect face during the next couple of years.

In order to validate VoLTE performance effectively, the carrier needs to define the correct QoS parameters over the complete LTE bearer path, which is not an easy task. All the individual sections of the path – user equipment (UE), Radio Access Network (RAN), Evolved Packet Core (EPC) and IP Multimedia Subsystem (IMS) core – need to be correctly optimised to ensure that the best performance is achieved and maintained throughout the high definition voice call, without dropping before the call is ended by the user.

VoLTE exploits the superior data capabilities of LTE to provide revenue-generating voice services on the same 4G network. Because data is now the dominant service and voice services represent just one of the traffic flows, VoLTE must compete for bandwidth with other applications such as video and data, which means it must be validated under realistic traffic conditions while these applications are running. When subscribers are moving rapidly or call handover takes place, this data is even more difficult to obtain.

Crucially, operators need to assess how many packets are dropped and whether there is any package delay on delivery. This needs to be scaled to hundreds of calls under real-world conditions. Testing individual calls would not give an adequate indication of the scalability of the service when voice is under contention with other high-bandwidth network traffic.

Before using real mobile devices on the network, the operator can use a TM500 network tester to prove that it is capable of handling hundreds or thousands of VoLTE users moving around in a multi-technology environment, falling back to 3G and 2G from LTE when necessary. Sometimes the launch of a new gaming app like Pokémon Go, or a large number of users watching live Olympic coverage on their mobile devices, can cause a sudden change in the profile of network traffic. Operators prefer to emulate scenarios like this prior to launching the service, rather than to suddenly see an issue on the live network causing a high level of activity at the call centre or online self-help application.

The ‘per-flow’ emulation and test approach used in the TM500’s virtualised IP test engine greatly simplifies the challenge of optimising the LTE network, enabling carriers to rapidly begin to monetise 4G voice services. With its unique approach to emulation and real time analysis, operators and network equipment manufacturers can delve down into the properties of a single emulated UE to visualise the end user’s individual quality of VoLTE experience in real time. This allows them to ensure that any changes in the IP network configuration or patterns of usage will have a minimal impact on subscriber services.

The end result of expertly validating VoLTE is a win-win situation: the operator will be able to offer high definition voice services and to achieve greater utilisation from existing infrastructure, while at the same time growing subscribers by delivering an exemplary service at the right price.

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