4G VoLTE Networks to be Powered by IMS Core

If you have been following the Telecommunications industry for a decade or more you will likely remembers IMS (IP multimedia system) as the technology architecture developed by the leading circuit switch voice vendors (i.e., Lucent and Nortel) in the late 1990s as the technology that would save their declining voice businesses but they were far ahead of time.

This vision eventually came to fruition, but in a much smaller way in the long-distance network (4ESS) which was rebuilt using soft switches and media gateways to enable the use of VoIP to save money in the core by moving away from the more rigid circuit-switched network. Eventually, session border controllers (SBCs) also came into use as a way of enabling SIP trunking, another cost saving architecture. Even with these measures, however, the local networks – including current 2G and 3G wireless networks – still relied on circuit switch technology.

IMS has finally found a home in the network as the technology underpinning for VoLTE. It allows carriers to recycle spectrum by doing what IMS was intended to do: united fixed and wireless networks in one Next Generation Network by running voice and data over IP, which unleashes better voice quality and advanced features.
IMS Subsystem and VoLTE Arhcitecture

IMS architecture includes various elements such as the Call Session Control Function (CSCF) server and the Home Subscriber Server (HSS), also known as User Profile Server Function (UPSF). The CSCF provides call state functions including mapping phone numbers to an IP address. The HSS or UPSF contains subscriber profiles, which includes the documentation of the services that the subscriber has purchased. The CSCF accesses the HSS via diameter signaling technology.

Wireless SBCs, provide security and media conversion. These differ from their wireline cousins by being deployed in a “distributed” architecture where the control plane and media path are separated into different boxes to allow for greater scalability in the number of sessions supported. This is similar to the concept used in software-defined networking, with the IMS core swallowing the control plane function in many vendor solutions.

Wireless Voice Application Servers (VAS), house applications and therefore are more of a success-based sale, i.e., we expect a carrier to purchase more VAS licenses as more subscribers begin using VoLTE. And just as important, in order to actually use the VoLTE network, a subscriber needs a phone that’s VoLTE-enabled. There are 92 models of smartphones available in the Market (including carrier and frequency variants) that support VoLTE.

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