EMM, ECM and RRC states

Key Words: 

1. Evolved Packet System (EPS)
2. Mobility Management Entity (MME)
3. Non-Access Stratum (NAS)
4. EPS Mobility Management (EMM)
5. EPS Connection Management (ECM)
6. EPS Session Management (ESM)
7. Radio Resource Control (RRC)

EMM (Involves the UE and MME)

• State 1: EMM-Deregistered; UE is not attached to any LTE network. MME does not know the current location of the UE, but may have tracking area (TA) information last reported by the UE.
• State 2: EMM-Registered; UE has been attached to the LTE network and an IP address has been assigned to the UE. An EPS bearer has been established. The MME knows the current location of the UE with an accuracy of a cell or, at least, a tracking area.

ECM (Involves the UE and MME)

• State 1: ECM-Idle; No NAS signalling connection (ECM connection) established yet. UE has not been assigned physical resources, i.e. radio resources (SRB/DBR) and network resources (S1 bearer/S1 signalling connection) yet.
• State 2: ECM-Connected; NAS signalling connection (ECM connection) is established. UE has been assigned physical resources, i.e. radio resources (SRB/DRB) and network resources (S1 bearer/S1 signalling connection).

RRC (Involves the UE and eNodeB)

• State 1: RRC-Idle; No RRC connection is established yet.
• State 2: RRC-Connected; RRC connection has been established.