Voice Over LTE
Voice is perceived to be the most important service supplied by today's communication service providers for their end users. In this sense, voice also represents an important service when considering the commercial LTE service portfolio despite the fact that early deployments of LTE may be more related to datacentric services such as browsing or video. In the early stage of LTE standardization it was decided that LTE architecture would no longer have Circuit-Switched technology , similar to that used as the backbone of today's mobile networks. This brought number of new challenges for communication service providers who have to provide voice and Short Message Service in a new manner without increasing the time schedule and complexity of the overall LTE deployment project. Initially, this issue was considered in 3GPP to be handled with the introduction of IP Multimedia Subsystem (IMS)  but it turned out that deployment of this technology was not yet mature enough to be used in some networks.
This issue was enough to drive industry to push a number of different rather fragmented alternatives for voice over LTE. These alternatives ranged from use of the CS network to provide voice services for LTE attached subscribers with the Circuit-Switched call-control protocol stack all the way to more radical alternatives that use third-party VoIP services, such as those that are currently ...