Mobile Packet Core

The Mobility Management State, 'MM state', is a parameter exist in the 'MM context' established on the UE, and the SGSN after the 'attach procedure'.

The MM state is having three different values, which describes the state of the UE from Mobility Management prospective as shown below,

READY state,

In READY state, the network knows the UE exist in which location to the most accurate level, which is the cell level.

In addition, the packets can be normally sent between the UE and the SGSN.

The UE enters to READY state when it makes the 'Attach procedure'. 

STANDBY state,

In STANDBY state, the network knows the location of the UE only to the RA level. it doesn't know the UE exist under which cell in this RA.

In this state, no packets can be sent or received between the UE and the SGSN.

There is a timer exist on the UE and SGSN called the 'READY timer'.

If the 'READY timer' expired ,without sending or receiving any packets ,between the UE, and the SGSN, the MM state will move to STANDBY state in order to save the resources of the network.

Then if any packet to be sent , or received , between the UE, and the SGSN, the MM state , will return again, to READY state.

IDLE state,

In IDLE state, the network doesn't know about the existence of the UE.

The UE moves to IDLE state when it makes a 'Detach procedure'.

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