Voice over LTE. VoLTe. You've no doubt heard of it by now, and chances are many of your calls utilize the technology. But why is VoLTE so huge and why are carriers rushing to roll it out across their networks?

To dig a little deeper, Wireless Week got in touch with John Wick, SVP and GM of Syniverse, a company intimately involved in the transition to VoLTE. Here's what he told us:

[Wireless Week] What’s the case for the shift toward VoLTE over traditional services? Why are operators drawn to it?

[John Wick, Syniverse] The shift toward voice-over-LTE (VoLTE) continues to grow because traditional voice calling services have limited efficiency and quality. VoLTE offers a richer multimedia voice experience for the user and reduced costs and complexity for the mobile operator.

One way VoLTE reduces complexities and costs is by eliminating the need for operators to have voice and data services running on separate networks. Traditional voice calling services have been based on call location and duration over a circuit-switch network. VoLTE calls, on the other hand, are sent over a LTE network based on data – using KBs and MBs. This allows operators to consolidate their voice and data equipment and various services with everything traversing a LTE network. Furthermore, operators are drawn to VoLTE for its added benefits of faster connections between callers with improved call setup times and more control over a roamer’s voice traffic.

Operators can also leverage VoLTE to provide high-quality services that further induce revenue generation. For example, VoLTE has increasingly become an attractive service for end users and businesses because it allows users to move from voice to video, share files, send text messages, and access the internet and social media, all within a single session. Operators that offer these services via VoLTE are differentiating their brands, which will reduce subscriber churn, and ultimately bring greater efficiency to their business.

[WW] Can you dig deeper into how the implementation of VoLTE is changing carrier networks? How is it impacting not only the physical infrastructure and equipment, but also the way they price their services and measure quality of experience?

[JW] For successful implementation of VoLTE services, operators must invest in IP Multimedia Subsystem (IMS), which is designed to support multimedia sessions over an all-IP, LTE environment. Among other elements, IMS includes a call session control function (CSCF) and a border control function to address communication between SIP applications, network topology hiding, signaling exchange, and charging detail records. The IMS foundation that helps power VoLTE services will remain a critical next work element in LTE-based voice, video, and media services, while also establishing a platform for launching next-generation mobile solutions.

Another way VoLTE is further changing operators’ networks is by adding a need for a policy and charging control (PCC) element. The PCC is necessary to establish consistency between the subscriber, services offered and how the service is being used. The PCC also offers innovative services, packaging, pricing, and additional controls quality of services.

VoLTE is transforming operators’ pricing and billing models because multiple services can be used simultaneously while making a voice call over LTE. This could include support for a voice call while another data application is being used, such a video call. In this case, the operator may choose to charge the video as data instead of voice just as it would other streaming video services. However, operators and their subscribers may have different views of how services are being used. For example, a mobile operator may consider a LTE-based voice call as data, while the call may be considered as a phone call from the subscriber’s point of view. As a result, operators need to be able to distinguish between data and voice to bill the service accordingly.

[WW] How do interconnect and roaming services play on VoLTE networks?

[JW] Both VoLTE interconnect and VoLTE roaming have the same goal of connecting two VoLTE-enabled devices over LTE, but there are some critical distinctions between the two services.

Interconnect enables a subscriber to call another subscriber on a different network within their home market. The action of interconnect is non-roaming and a call typically runs through multiple networks to facilitate the connection to a specific destination. In a VoLTE interconnection scenario, the call session is handled between two operators through one single, secure IP-based IPX network.  

VoLTE roaming, on the other hand, enables a subscriber traveling outside of their domestic coverage area to utilize another operator’s network as a visitor. For VoLTE roaming, mobile operators are faced with two main implementation options: local breakout and S8-home routing.

The local breakout option closely resembles what’s presently used for 3G calls. The signaling associated with the call is routed via the home network to provide evolved features and capabilities that the visited network can offer, with the final media path being routed by that visited network.

For S8-home routing, both the signaling and the media associated with the call are routed back to the home network as a data connection, and neither the visited network nor IPX provider is aware that it is a VoLTE roaming call. This option enables operators to control the call from start to finish, as well as send the call back to the home network using IPX transport or data roaming.

Both local breakout and home routing options come with their set of complexities and benefits for operators, so IPX providers should be prepared to support both.

[WW] What does the future hold for VoLTE?

[JW] VoLTE is expected to continue to gain popularity at a steady rate. One of the latest industry reports from the GSA shows that nearly 200 operators are investing in VoLTE across 90 different countries. In fact, more than 100 networks are VoLTE capable, 36 VoLTE networks are in deployment, 25 VoLTE networks are planned or are testing, and the growing selection of “capable” VoLTE devices is over 430.