Wednesday, January 21, 2009

EPS Mobility Management and Connection Management

I was reading the spec 3GPP TS 23.401 v8.4.1 (GPRS Enhancements for E-UTRAN) today. Below is what i could make out about EPS Mobility Management (EMM) and EPS Connection Mangement (ECM).
Two states of EMM (EMM-Registered and EMM-Deregistered) and two states of ECM (ECM-IDLE and ECM-Connected) were described in the document. EMM states describe the mobility management statest that result from the mobility management procudeures e.g Attache and Tracking area update procedures.
ECM states describe the signallin gconnectivity between the UE and EPC. Definition of EMM States: EMM-De-registered : In the EMM‑DEREGISTERED state, the EMM context in MME holds no valid location or routeing information for the UE. The UE is not reachable by a MME, as the UE location is not known. EMM-Registered : The UE enters the EMM-REGISTERED state by a successful registration with an Attach procedure to either E-UTRAN or GERAN/UTRAN. The MME enters the EMM-REGISTERED state by a successful Tracking Area Update procedure for a UE selecting an E-UTRAN cell from GERAN/UTRAN or by an Attach procedure via E-UTRAN. In the EMM-REGISTERED state, the UE can receive services that require registration in the EPS.The UE location is known in the MME to at least an accuracy of the tracking area list allocated to that UE (excluding some abnormal cases).
In the EMM-REGISTERED state, the UE shall:
- always have at least one active PDN connection;
- setup the EPS security context.
Definitions of ECM States: ECM Idle : A UE is in ECM-IDLE state when no NAS signalling connection between UE and network exists. In ECM-IDLE state, a UE performs cell selection/reselection according to TS 36.304 [34] and PLMN selection according to TS 23.122 [10]. There exists no UE context in E-UTRAN for the UE in the ECM-IDLE state. There is no S1_MME and no S1_U connection for the UE in the ECM-IDLE state. ECM Connected : The UE location is known in the MME with an accuracy of a serving eNodeB ID. The mobility of UE is handled by the handover procedure.
The UE performs the tracking area update procedure when the TAI in the EMM system information is not in the list of TA's that the UE registered with the network, or when the UE handovers to an E‑UTRAN cell and the UE's TIN indicates "P-TMSI". For a UE in the ECM-CONNECTED state, there exists a signalling connection between the UE and the MME. The signalling connection is made up of two parts: an RRC connection and an S1_MME connection.

EMM State Model in UE
EMM State Model in MME

ECM State Model in UE

ECM State Model in MME

1 comment:

Vimal Kumar said...

Nice explanation...