Practical Guide to LTE-A, VoLTE and IoT

3VoLTE/CSFB Call Setup Delay and Handover Analysis

3.1 Overview

The IP Multimedia Subsystem (IMS) is a framework for delivering all‐IP‐based services. Voice via IMS has been defined as a possible solution from 3GPP Release 5, prior to LTE. However, the cost and immediate need for IMS services prevented carriers from migration to IMS‐based services, especially with the widespread presence of circuit‐switched (CS) services offered in GSM and UMTS networks. CS fallback (CSFB), introduced in 3GPP Release 8, enables the support of a voice service without IMS. This is the commonly deployed scenario for many existing LTE networks. Voice over LTE (VoLTE) is compulsory in terms of offering rich communication services (RCS) via IMS in addition to improving the performance of the already‐deployed CSFB voice solution. However, CSFB and VoLTE are deployed concurrently, so carriers can gradually roll out an LTE/IMS system while still supporting a 2G/3G fallback mechanism. It is therefore important to benchmark the performance of both solutions, highlight the deployment challenges, and study the impacts on the end‐user experience. This chapter provides performance analysis, deployment challenges, and comparisons between these voice solutions. The chapter presents practical performance analysis including end‐to‐end assessment of call setup delay in different radio conditions, main challenges impacting the in‐call performance, and performance aspects of Single Radio Voice Call Continuity (SRVCC) ...