A question about SRVCC and CSFB

Dear User, 

CSFB is when the UE initiates the CS service, and the MME (Mobility Management Entity) instructs theUE to fall back to the target system CS network and then initiate the CS service. The CSFB feature is essentially a session establishment process, that is, the UE has entered the CS network before the CS session is established. During the entire CS call, the UE is always located in the CS network. The CS service includes services such as voice, short message, location, and emergency call. After receiving the CSFB instruction, the eNodeB handles various CS services in a unified manner. 

Single radio voice call continuity(SRVCC)

Voice call continuity between IMS over PS access and CS access for calls that are anchored in IMS when the UE is capable of transmitting/receiving on only one of those access networks at a given time. 

Thanks!

When UE is in LTE network and needs to use voice service if this UE does not support VOLTE, then it will use CSFB to fall back to 2G and use 2G to carry voice service, of course, fall back to 3G is also possible, because UE does not support VOLTE, all this case can not happen SRVCC. if UE supports VOLTE, support SRVCC, at this time LTE side is able to complete the voice service independently, do not need to fall back to 2/3G, also will not use CSFB technology, when the UE is doing voice service move to the edge of LTE coverage, because at this time the LTE signal has been very poor, not enough to support the voice service to continue, then SRVCC will occur, voice service from LTE bearing into by 2G bearing, all if LTE Network coverage is very good, SRVCC is relatively small.