Will 4G subscriber latch to 3G in absence of 4G network? what will be happen in case of VoLTE?

Question

Hi, what will be happened to 4G subscriber in absence of 4G network. Will he/she latch to 3G network? Especially in Punjab where 3G network is not available?

Answer 1

As per my knowledge, three concepts have been defined for VOIP services. Those are as followings:
1. CS fall back.
2. SRVCC

In case of SRVCC, when UE moves from LTE to UMTS, its VoLTE call will be moved to 3G gateway and it will be converted into CS call .In essence, a packet switched voice call will be converted into circuit switched call. Another way is to do CS fall back when UE moves to CS network and when its voice call is over it comes back.