VoLTE Tutorial- This Voice over LTE beginners guide will help you to understand the fundamentals of IP based voice communication in the 4G LTE network.
2G is a Circuit Switched (CS) network. 3G has both CS (Circuit Switched) and PS (Packet Switched) domains.
But, LTE, on the other hand, is an all-IP network. It does not have any CS domain.
LTE is great for packet data connectivity, such as the Internet. But it faces many challenges for traditional voice and SMS communication. Before LTE, mobile networks used CS domain for voice and SMS communication.
LTE 4G network uses VoLTE (Voice over LTE) as the technical solution to carry out voice calls over IP. IP stands for Internet Protocol.
To understand the topic, I divided the VoLTE tutorial into 5 small chapters.
You can skip one chapter and move to the next one. But if you are new to VoLTE, I will recommend you to read all chapters. This will help you to understand all basic concepts.
Here are the topics I am going to cover in this VoLTE tutorial.
- VoLTE History and Timeline
- IMS VoLTE Architecture
- VoLTE Deployment Evolution – CS only to Voice over IP in LTE Network
- VoLTE Call Flow and Procedures
- IMS SIP Requests and Codes
VoLTE History and Timeline
LTE is an all-IP network. Improved data throughput was the initial motivation behind LTE development. Standardization groups proposed IMS VoLTE as the solution to support voice and SMS over LTE network.
In this chapter, we will check the background of VoLTE and the motivation behind it.
Long Term Evolution or LTE depends on IMS (IP Multimedia Subsystem) to deliver voice calls. This chapter provides detail information about VoLTE architecture.
We will discuss the changes in User Equipment and EPC core. To support VoLTE, LTE network also requires IMS (IP Multimedia Subsystem)
LTE is an all-IP based network. LTE network does not support any CS based services. To deploy voice and SMS in the beginning, operators used intermediate solutions. In this chapter, we will discuss intermediate solutions like CSFB, SVLTE, and SRVCC.
CSFB stands for CS Fallback. SVLTE stands for Simultaneous voice and LTE. SRVCC is Single Radio Voice Call Continuity.
VoLTE Call Flow and Procedures
In this chapter, we will discuss two important VoLTE call flows.
- In the first call flow, we will discuss registration of an IMS/VoLTE UE.
- In the second call flow, we will discuss an end-to-end SIP VoLTE voice call.
SIP Requests and Response Codes
Session Initiation Protocol deals with the request-response mechanism. Also, we will note down all SIP response codes and their description.