SMF Serving Area, is a specific geographical region in the 5G network that a specific SMF instance is responsible for managing the User Equipments (UEs) that exist within this serving area.

The size and boundaries of this Serving Area are typically determined by the 5G network operator. This is based on factors like network infrastructure, service requirements, and user density.

The SMF is responsible for managing user sessions within its designated Serving Area.
This includes functions like session establishment, modification, and release. In addition to IP address allocation and management.

When a UE moves away from the SMF serving area in the 5G network, the AMF decides to either perform SMF relocation, or it can insert an I-SMF (Intermediate SMF).

Taking into consideration that inserting an I-SMF is a better choice, as it works as a session anchor point between the UE and the original SMF. Which maintains the user's IP address and other session-related information. This help maintain a better user experience