Supporting Voice over LTE: Solutions, Architectures, and Protocols

Modern cellular networks are expected to support both voice and a growing volume of data traffic. The rapid growth in data traffic has promoted network operators to move to Long Term Evolution (LTE), a 4th generation of wireless network infrastructure. However, LTE architecture does not support native circuit switching services and relies on the IP Multimedia Subsystem (IMS) for supporting voice and Short Messaging Service (SMS). Unfortunately, the uptake of IMS has not been as rapid as expected and deployments of IMS cores have been limited. This poses a major issue for operators who wish to deploy LTE in the near future. In particular, voice and SMS drive a majority of service provider revenue, who are concerned with voice quality, call continuity, and reliable SMS delivery in deployed LTE networks. In this paper we analyze several contending approaches to delivering voice services over LTE networks. Each approach will be illustrated with sequence diagrams to explain how voice and SMS services are rendered. We compare the proposed solutions in terms of complexity, cost, features, and interoperability.