VoLTE End to End and Signalling
This chapter gives a detailed example of voice over long term evolution (VoLTE) related procedures in end to end manner. Signalling procedures, protocol messages and their elements are described and explained based on an example. The reader will see how VoLTE signalling works and how previously described concepts and architecture are realised at the protocol level. Nevertheless, this part concentrates on straightforward examples and does not handle error or abnormal procedures in detail. To give a better understanding of the procedures applied, each section of this chapter concentrates on different concepts, such as VoLTE subscription, evolved packet system (EPS) attach and default bearer, voice domain discovery procedure, IP multimedia subsystem (IMS) registration, IMS voice over Internet protocol (VoIP) session, circuit switched fallback (CSFB) procedures, emergency session and messaging.
This chapter is based on the assumption that user Kristiina has just obtained a new long term evolution (LTE) mobile and wants to call her friend Jennifer who is living in the United States. Kristiina's communication service provider is in Finland and it offers VoLTE as the primary voice service but has not yet completed a full roll-out of LTE coverage. For securing end user satisfaction the communication service provider has also deployed a single radio voice call continuity (SRVCC) feature and IMS centralised services (ICS) to enable ...