Although LTE (long term evolution) is a packet-only technology, the standard was defined to efficiently handle voice and multimedia services, providing support for more than mobile Internet access. This chapter describes some of the main practical aspects on how to support telephony services over LTE/EPC (evolved packet core). An end-to-end approach is followed in this chapter outlining the requirements in the LTE radio access, EPC, the IMS (IP multimedia subsystem) core, and the voice application server. The chapter includes a description of the radio features for voice, how QoS (quality of service) is provisioned to support conversational speech, IMS features for voice telephony, media handling, roaming architecture, and how to take advantage of any existing circuit-switched infrastructure.
A general view of the network transformation toward VoLTE (voice over long term evolution) and all the added-on services is shown in Figure 7.1.
To understand how LTE can support voice services in the packet-switch domain, this section explains the basics of the VoIP (voice over Internet protocol).
To understand the “basics” of VoIP, one must be familiar with the IP (Internet protocol) stack and the difference between different protocols ...