I ran across this image showing S-GW interfaces and I noticed S-GW in EPC is connected to RNC in UTRAN core by S12 interface.
I am trying to understand why is there a connectivity between S-GW and RNC ? Is it because of 4G-3G handover ? If that’s so, shouldn’t it be taken over by MME?
Also, why S-GW is connected to only RNC ? Why is not connected to BSC as well for 4G-2G handover (in case 3G is not present in a network or area)?
Many thanks in advance.