What is MME In LTE-4G? 

The MME full form is Mobile Management Entity. It is the network node in the LTE-EPC located in VPLMN. MME connects to the UE via eNodeB. Towards the core network, it connects over various protocols (LTE-Interfaces). In this tutorial, we will explain the interfaces with MME along with network management procedures.

S1AP Interface.

The signaling interface between MME and the eNodeB. UE attaches to the network using S1Ap protocol procedures. An eNodeB configures the MME address and sets up an SCTP association, and completes an S1AP Setup procedure before sending any UE activity messages.

To attach UE, the Initial-UE is the first message from eNodeB.

S11 Interface:

The S11 interface is a GTP-C-V2 (Version 2) based Interface with the SGW. During attach and other activities via UE, SGW does signaling with the PGW in-home network over the s5/S8 interface. SGW set up the logical tunnels with PGW. The eNodeB sends user data packets to the SGW using the GTP-U data plane protocol.

S6a Interface:

This is an interface with the HSS. It is the node that holds the subscription data for a subscriber. The HSS may be co-located with the AUC for the 4G authentication. S6a uses a diameter protocol over SCTP.

T6a interface:

The T6a interface is a diameter protocol interface with the SCEF for the Non-IP data delivery in the IoT network.

UE Attach procedure in MME.

Till now, we have described key Interfaces of MME. Here we will explain the initial attach procedure to understand the basic functionality of the MME in the LTE network.

When UE switches on, it sends an Initial UE message with Attach request for PDN connectivity to the MME. In turn, MME starts the MAP send-authentication-info procedure with the HSS/AuC for requesting authentication vectors. 

After successful authentication, MME initiates an Update Location procedure for the subscriber information.

MME sends the authentication request to the UE. Once UE verifies that vectors are suitable. UE sends an authentication response. After authentication, MME sends a create session request to the SGW over the S11 interface.

To create a session success response, MME sends an Initial Context setup request with the GTP-U plane address of SGW along with other parameters. If UE sends the Initial Context Setup Response. And then Attach accept.