S1 - This is the interface between eNode Bs and MME and S-GW. In the user plane this interface will be based on GTP User Data Tunnelling (GTP-U) (similar to today’s Iu and Gn interface).
In the control plane, 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.
It has been agreed to split the S1 interface into a S1-CP (control) and S1-UP part (user plane). The signalling transport on S1-CP will be based on SCTP. The signalling protocol for S1 is called S1-AP.
S1 is a many-to-many interface.
LTE S1 Interface
