SRVCC - DRVCC

aSRVCC = SRVCC during alerting stage 

bSRVCC = SRVCC before alerting stage 

eSRVCC = enhanced SRVCC, which is a network feature for reducing audio delay from SRVCC 

rSRVCC = SRVCC in the reverse direction CS call to VoLTE call 

vSRVCC = Single Radio Video Call Continuity

mid-call SRVCC = SRVCC which allows both active and held calls to be transferred from VoLTE calls to CS calls

DRVCC = Dual Radio Voice Call Continuity