Question: why srvcc is called single radio?
Answer: SRVCC stands for Single Radio Voice Call Continuity. Putting it simple, it is a Handover technology between "VoIP over IMS in LTE" and Voice Call (CS) in a legacy system (e.g, WCDMA). It means it is for Handover between a Packet call in LTE and a Circuit Call in a legacy system (WCDMA).