LTE ECM/EMM AND RRC STATES

EMM and ECM states

There are two sets of states defined  for each UE based on the information held by the Mobility Management Entity.

EPS MOBILITY MANAGEMENT

The two EPS Mobility Management (EMM) states, EMM-REGISTERED and EMM-DEREGISTERED describe whether or not the UE is registered to MME and can be reached by paging.

In EMM-DEREGISTERED state the MME hold no valid location information for the UE. The UE is not reachable since its location is not known.
UE enters EMM-REGISTERED state either due to LTE attach procedure or due to a tracking area update (TAU) from IRAT.  In this state UE can be reached by paging.

EPS CONNECTION MANAGEMENT

The two EPS Connection Management (ECM) states ECM_IDLE and ECM-CONNECTED, describe the signalling connectivity between UE and Evolved Packet Core.

In ECM-IDLE state, there exist no signalling connection between UE and the MME.
In ECM_CONNECTED state there exist a signalling connection between UE and MME. This signalling connection consist of two parts:
an RRC connection between UE and eNodeB, and an S1 -MME connection between eNodeB and MME.

EMM and ECM states

EMM-DEREGISTERED & ECM-IDLE ⇒ RRC_IDLE:
- Mobility: PLMN selection.
- UE Position: not known by the network.


EMM-REGISTERED & ECM-IDLE ⇒ RRC_IDLE:
- Mobility: cell reselection.
- UE position: known by network at TA level.

EMM-REGISTERED & ECM-CONNECTED with RB established ⇒ RRC_CONNECTED.
- Mobility: handover.
- UE Position: known by the network at cell level

Tune in For more.. :)