VOLTE VOIP IMS SIP CSFB

Often people are confused between VOLTE ,VOIP, IMS , SIP and CSFB.
To be clear between all this item lets explain them and understand one by one.
We will start with CSFB and then VOIP and then VOLTE and IMS.

CSFB - CSFB is CS Fall back.
             This was introduced at the very early stages of 4G/LTE to make CALL's as because LTE has
              been PS from the beginning and over PS LTE was not having any standard offerings for
              calls. Because of not having call support 3GPP standard decides to use to use CS over
              legacy network.
VOIP - Now VOIP is Voice Over IP. Frankly speaking there is no relation between VOIP and LTE.
             VOIP can be used over PS and it could be from 2G , 3G or LTE or may be Wi-Fi even over
             the LAN as well.
VOLTE - VOLTE is Voice Over LTE. The much talked feature of LTE without which LTE was not
                complete Conceptually it it Voice-Over-IP On LTE , but there is a lot more to it than just
                VOIP.
IMS - IMS is IP Multimedia Subsystem. This is a concept for an integrated network.
          This is not a protocol at all.
SIP - Session initiation protocol. This is an application layer protocol. This can establish modify and
         terminate multimedia session.


So in one line VOLTE is an VOIP over LTE which uses SIP protocol over IMS architecture.