What is SRVCC?

The SRVCC  full form is Single Radio Voice Call Continuity.  The SRVCC capability enables handover from a voice call over LTE based packet network to the circuit-based network SS7 network.  The LTE uses IMS for a voice call over the packet network. This does not involve setting up a dedicated voice channel. While in a circuit-based network (e.g SS7) E1 or T1 channels for voice calls are reserved.  During a call, a subscriber may move to the network where only a 3g or 2g network is available.

SRVCC provides uninterrupted call experience from VoLTE to 3G or 2G networks.

While registration to the home network during attach, the MME sends the SRVCC capability in the Update Location Request (ULR) message to the HSS.