Meeting The Requirements For Voice Over LTE (VoLTE)

Motivations for Enabling Voice over LTE

The motivation for the deployment of 3GPP Long-term Evolution (LTE) mobile broadband technology is simple: All things considered, LTE delivers to carriers the lowest cost-per-transported bit. That said, the adage that “voice pays the bills” still applies: though in decline, carriers continue to derive the bulk of their revenues from voice and integrated messaging services.

In the context of LTE, this presents a dilemma. A fundamental aspect of legacy technologies such as GSM, UMTS, and cdma2000 is that they possess integrated services: voice, voice supplementary services (e.g., call forwarding), short messaging, etc. In contrast, LTE makes no such provisions: it is subscriber service-agnostic. Further, LTE is a pure packet technology, with no inherent conception of a circuit-switched (CS) bearer, on which legacy voice services depend.

Because of the realities of the cellular revenue model – and, indeed, because cellular subscribers expect service continuity – the question arises: How can we best deliver voice and other legacy services via LTE? As with any engineering exercise, this requires articulation of the requirements.