Practical Guide to LTE-A, VoLTE and IoT

2Introduction to the IP Multimedia Subsystem (IMS)

2.1 Introduction

In this chapter, we will introduce the IP Multimedia Subsystem (IMS), which is the core network of Voice over LTE (VoLTE). We will focus on IMS architecture, IMS core network elements, and the IMS core network call and signaling flow between different network elements. In addition, the chapter will cover practical deployment scenarios for IMS‐network‐based real use cases from a live network deployment. Moreover, the high‐level design (HLD) of a practical IMS system will be presented, addressing key design aspects. Although, the IMS target is to be the core for all IP multimedia communication traffic, we will focus only on VoLTE in this chapter. Other IMS services such as Voice over Wi‐Fi (VoWiFi), Video over LTE (ViLTE), and Web Real‐Time Communication (WebRTC) are not discussed in detail. Our aim in this chapter is to provide the reader with the foundations of IMS, which will be necessary when we reach the VoLTE practical performance analysis provided in Chapters 3and 4. IMS can also support access modes such as Wideband CDMA (WCDMA), Code Division Multiple Access 2000 (CDMA2000), Wi‐Fi, xDSL, local area network, PSTN/integrated services digital network (ISDN), and worldwide interoperability for microwave access (WiMAX).

2.1.1 Voice over LTE Overview

As mobile broadband networks continue to evolve, mobile broadband has become a development trend for mobile speech services that rely heavily on soft switch. The radio ...