other two applications. LTE Small Cell Optimization Streaming applications Power Payload Signalling App 1 App 2 App 3 Figure 16.20 Music streaming application performance comparison Voice over LTE LTE networks are designed for packet switched connections and do not support circuit switched voice. During the initial phase of LTE network deployment, operators have relied on solutions such as Circuit Switch Fall Back (CSFB) or dual radio devices connected simultaneously to LTE and 2G/3G voice networks, to provide reliable voice service. However, with the extension of LTE coverage and proliferation of third-party VoIP services, operators need their own solutions for voice over LTE (VoLTE). At the same time, there are already a number of applications providing over the top (OTT) voice service on smartphones which can be used not only over Wi-Fi connection but also over cellular networks. The voice quality and the mobility performance of OTT voice service not guaranteed and depend on the instantaneous network conditions. The aim of this section is to provide a general benchmark between VoLTE and different types of voice clients over LTE network, looking at both user experience and impact network performance. In addition, legacy circuit switched voice service is used as reference for quality and battery consumption. Different types of VoIP applications can be classified into three categories: Native VoLTE clients: Embedded VoLTE client which is integrated in the phone software. At the time of testing only a few commercial terminals with native VoLTE clients were available, but more are expected to become available over time. Non-native VoLTE Session Initiation Protocol (SIP) clients: Third-party applications which can register to IP Multimedia Subsystem (IMS) and establish VoLTE call using Quality of Service (QoS) Class Identifier 1 (QCI1). Smartphone Optimization Over the Top VoIP: Third-party applications which allow voice or video calls over default non-Guaranteed Bit Rate (non-GBR) bearers, usually for free. For ben