LTE: What is the Paging Proceed Factor (PPF) flag and its importance ?

Question

When the PPF flag is used ?

Answer 1

MME maintains Paging Proceed Flag in the UE mobility context. If this flag is activated , it means MME will trigger Paging procedure when UE would be in the ECM-IDLE mode and SGW sends downlink data notification message to MME.

MME reset this flag when mobile reachable timer expires. When SGW receives data from PGW for an UE and triggers downlink data notification towards MME since this flag is not set, MME does not perform paging procedure for that UE in the E-UTRAN coverage and responds back to SGW with the Downlink Data Notification Reject message.

Comments

Just to add on what Vimal told here. After expiry of mobile reachable timer, MME starts implicit detach timer and on the expiry of implicit detach timer, MME changes the state to EMM-DEREGISTERED but still maintain the context with UE's GUTI and Security Context since UE may come to the network again soon.