Circuit Switch Fallback (CSFB) is used when voice services can not be provided through LTE network due to limitation of either network or UE. If this case, UE does combined attach with MME and as part of combined attach, UE registers with MME as well as MSC of 2G network. For mobile terminating/originating voice call, UE sends Extended CS service request to MME and MME sends UE Context Modification to redirect the UE to GSM network. As part of CSFB, only radio and S1 bearers are released at LTE network and context is still maintained at MME. Since as soon as voice call gets over, UE switch to LTE network.
Single Radio Voice Call continuity (SRVCC) is a solution which is used when both UE and LTE network was capable for VoLTE but due to limited 4G network coverage, UE moves to UMTS network and receive the same voice all through LTE and UTMS interworking. In this case, UE still will be in registered state and all the non-GBR bearers will be in suspended state and all the dedicated bearers will be released.
SRLTE is known as Single Radio LTE and this technology is developed by Apple. By having this technology, UE can registers with CDMA and LTE simultaneously and after the successful registration to both the network. I don't know have much information on SRLTE.
