The main EPS mobility management states are shown below.
EMM = EPS Mobility Management
In this state the location of the UE is not known by the network ( e.g., UE is powered off )
There is no EMM context in the UE.
It is a null state in which the UE enters before getting attached, meaning before UE is powered on and UE is not known in the network. Known UEs will either be in EMM-IDLE or EMM-CONNECTED states.
In this state, the location of the UE is known by the MME at the level of tracking areas.
For Mobility purposes in this state cell reselection is still performed by the UE and tracking area updates are send to the network.
In this state there exists a signaling connection between UE and the MME.
The location of the UE is known at cell level
In this state UE is known on cell-basis. Mobility is network controlled and assisted by UE measurement reports.
In this state data transmission can take place with limited delays and should support lower UE power consumption mechanisms such as DRX/ DTX periods etc.