MME node functionality

What is the functionality of the MME node ?

The EPS architecture defines an MME node, which contains CN control functionality.

Although the functionality is not entirely the same, the MME conceptually constitutes a CP SGSN node.

The CP terminal protocols terminate at the MME which also manages the mobility contexts of the UEs. The same MME remains in control of a UE as long as the UE move within an MME pool area.

Below follows descriptions of the functions performed by the MME.

The MME handles the mobility and session management functions listed below:

• UE attach/detach handling - This allows UE to register/de-register to the network.

• Security – AAA
The Access Gateway (AGW) implements functions for Authentication, Authorization and Accounting (AAA) to verify users’ identities and grant access to the network and track users’ activities. In addition, the MME performs ciphering and integrity protection of NAS message signalling.

• EPS Bearer Handling
The MME manages the setting up, modification and tearing down of EPS Bearers. It is assumed that a UE in E-UTRAN will always have one default EPS Bearer established at the time of attachment to the network.

• Mobility Anchor – IP Point of Presence
The AGW acts as a mobility anchor point which hides UE mobility from the fixed network. When a UE attaches to the network it is assigned an IP address from an AGW which then also assumes the role of mobility anchor to the UE. While the control of a UE may be transferred to another AGW because of a HO, the UEs IP Point of Presence (PoP) will remain at the mobility anchor AGW. Thus, the mobility of UEs is transparent to the fixed network.

• Mobility Management for Idle Mode UEs
The MME manages mobility of idle mode UEs. Idle mode UEs are tracked with the
granularity of Tracking Area (TA).