LTE-4G: EPS Mobility Management and Connection Management

Difference between EMM and ECM

EMM [EPS Mobility Management ]

There are two states :

1.Registered

2.DeRegistered

1.Registered :

Ue can enter into this state by,

a.Attach

b.I-RAT[Inter RAT ] TAU

In this state UE atleast has 1 active PDN connection and EPS security context

The UE location is known in the MME to at least an accuracy of the tracking area list allocated to that UE

2.DeRegistered :

Ue can enter into this state by,

a.Attach Reject

b.TAU Reject

c.On Detach

d.On successful I-Rat Handover

In this case Routing info is not available to MME and UE is not reachable

In the EMM-DEREGISTERED state, some UE context can still be stored in the UE and MME, e.g. to avoid running an AKA procedure during every Attach procedure

ECM [EPS Connection Management]

There are two states :

1.IDLE

2.Connected

1.IDLE :

A UE is in ECM-IDLE state when no NAS signalling connection between UE and network exists.

There is no S1_MME and no S1_U connection for the UE in the ECM-IDLE state.

The signalling connection is made up of two parts: an RRC connection and an S1_MME connection.

The UE shall enter the ECM-IDLE state when its signalling connection to the MME has been released or broken.

The S1 release procedure changes the state at both UE and MME from ECM-CONNECTED to ECM-IDLE.

In the EMM-REGISTERED and ECM-IDLE state, the UE shall

a.Do a periodic TAU to notify EPC that UE is available

b.Do a TAU when the current TA is not in the list of TAs received when UE was registered

c.When RRC connection was release with 'LOAD Balancing TAU required' cause

d.Send Service request when it wants to send uplink user data or upon receiving paging

e.Do TAU when change of the UE's Core Network Capability information

Initial NAS messages that initiate a transition from ECM-IDLE to ECM-CONNECTED state are Attach Request, Tracking Area Update Request, Service Request or Detach Request

2.Connected

Here UE's location is known to the accuracy of serving ENB

There exists s1-MME connection and RRC connection

ECM-UE