What is Single Radio Voice Call Continuity (SRVCC)?

Along with LTE introduction, 3GPP also standardized Single Radio Voice Call Continuity (SRVCC) in Release 8 specifications to provide seamless continuity when an UE handovers from LTE coverage (E-UTRAN) to UMTS/GSM coverage (UTRAN/GERAN). With SRVCC, calls are anchored in IMS network while UE is capable of transmitting/receiving on only one of those access networks at a given time.

See Evolution of Single Radio Voice Call Continuity (SRVCC) for more details.