For CS Fallback, MME will convert PS to CS switching.
The flow goes like following :
MO cal :
UE sends ESR to mme, mme gives the switchover command to ENB, ENB make UE to other technology fallback(handover). Then the call continous in other tech (3G or 2G).After call finishes it is upper layer job to reselect the ENB.
Terminated call :
MSC send the paging request to MME via SG interface. MME forwards to UE, Then UE will start ESR to MME, Then same flow contineous as per above flow.