Question

what mme does once mme gets ULA(update location answer ) from HSS with respect to egtpc?
what all scenario are available ?

Answer 1

Update Location Procedure is used by MME to update the current location/serving network of UE/IMSI at HSS.
In order to do this, MME prepares and send Update Location Request message to HSS and HSS responds with subscription-details.
Based on the received subscription-detail from HSS, MME triggers EGTP-C message "Creates Session Request" message towards SGW.

Answer 2

MME starts creation of default bearer based on subscriptions details got from HSS in update location answer

Answer 3

I just want to add few more context here. After getting the update location answer message, MME retrieves the PGW IP address from the ULA message and initiates create session procedure towards that PGW. MME selects SGW based on the UE location (ECGI + TAI) to further proceed with initiated Create Session procedure.