What is the advantage of using VoLTE and not useing CSFB?

Question

In LTE all operators use CSFB, my question is if they start using VoLTE then what would they gain or simply why operators use CSFB in place of VoLTE?

Answer 1

The simplest reason is that it is easy and cost effective. CSFB leverages existing architecture and only slight modifications are needed to fall back to legacy network for voice call. However for VoLTE, IMS platform is required that is huge investment compared to CSFB solution.

Answer 2

I don't know exact reason giving CSFB to high priority over the VoLTE. But in my personal view, for voice service, lte network need to setup a bearer with QCI = 1, which ask to reserve more resources. In LTE , objective is best use of radio resources. Since voice packets come with some interval(few milliseconds) i.e. no continuous bit stream, no re-transmission, reason being operator would like to prefer CSFB rather than creating a dedicated bearer to serve voice.

There may be another set of reasons to prefer CSFB over the VoLTE.

Answer 3

I will second the opinion of Faisal. IMS requires some good investment
So if you have legacy network why not use it. Most of the time footprint of legacy networks is greater than LTE. You will have more resources in LTE for data.
VOLTE has its own advantages like less call setup time and crisp voice quality which cannot be provided by legacy networks.