If the existing MMEs and CUPS-based S-GWs/P-GWs on the live network are selected to deploy the 5G NSA network and they remain unchanged, the existing MMEs may form a hybrid pool with 5G MMEs.
This feature enables the EPC+ to select a dedicated core network (DCN) for UEs based on the UE type in this networking scenario.
As shown in the following figure, when a 5G NSA UE accesses an EPC MME, the EPC MME sends a Reroute message to the eNodeB.
After receiving the message, the eNodeB forwards the message to the 5G MME.
Source: Sign Up | LinkedIn