SRVCC
SRVCC is Single Radio Voice Call Continuity, It is 4G network feature that allows ongoing voice calls to be seamlessly transferred between 4G and 2G/3G Radio Access Networks. SRVCC feature is required for 4G VoLTE networks which do not continuous RF Coverage and coverage gaps are filled with 2G/3G RF coverage .
We can see above picture for example, where we have 2G/3G cell having a wider coverage and 4G Cells with small coverage foot prints. When a UE moves from one 4G cell to another 4G cell due to no-overlap 4G coverage UE has to go through 2G/3G Coverage. So When UE is in Voice Call session and moving though 4G and 3G/2G Coverage it needs to have Voice Continuity for good user experience.
So with SRVCC feature enable UE can be easily handover from 4G Cell to 2G/3G Cell and Voice call session will continue and User will not notice and interruption. UE may observe it is a single cell with allowing the Voice Continuity.
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