LTE : S1 Interface

S1 Interface is the interface that connect eNB to EPC. The Interface is devided into two part :

S1 - MME Interface

• Control interface between eNB and MME
• Signalling protocol is S1AP : S1 Application Protocol
• Signaling transport based on SCTP
• MME and UE will exchange non-access stratum signaling via eNB through this interface ( i.e. authentication, tracking area updates)
•  the interface is more similar to Radio Access Network Application Part (RANAP), with some simplifications and changes due to the different functional split and mobility within EPS.

S1 - U Interface

• User plane interface between eNB and serving gateway
• Pure user data interface (U=User plane)
• The interface will be based on GTP User Data Tunnelling (GTP-U) (similar to today’s Iu and Gn interface)