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One principal goal in the evolution to LTE is the ability to deploy Voice over IP (VoIP) services such as Voice over LTE (VoLTE) alongside other services that use high-speed data. Toward that end, our industry has fittingly emphasized the realization of an IP Multimedia Subsystem (IMS) and its associated Session Initiation Protocol (SIP). IMS provides the interconnect/gateway functionalities that allow VoLTE devices to communicate with non-VoLTE devices or even non-wireless devices. SIP defines the signaling necessary for call establishment, tear-down, authentication, registration and presence maintenance, as well as, enabling supplementary services like three-way calling and call waiting.
However, focusing on these two areas overlooks the most significant goal of VoLTE: Delivering “carrier-grade” (or “telco-grade”) voice services that subscribers perceive to be as good as—or better than—legacy voice services.
This concept fundamentally differentiates VoLTE from other VoIP services. Ensuring “carrier-grade” voice requires the marriage of IMS and SIP with a number of LTE Radio Access Network (RAN) features. It is this combination of IMS, SIP and RAN features that ultimately provides the “carrier-grade” VoLTE experience. This white paper identifies new and necessary RAN features and discusses how each improves the quality of VoLTE service.
The white paper is part of a suite of associated literature available from Spirent. Others include: