S1AP provides the signalling service between E-UTRAN and the evolved packet core (EPC) and has following functions:

• E-RAB management function
• Initial Context Transfer function
• UE Capability Info Indication function
• Mobility Functions
• S1 interface management functions
• NAS Signalling transport function
• S1 UE context Release function
• UE Context Modification function
• Status Transfer
• Trace function
• Location Reporting
• S1 CDMA2000 Tunneling function
• Warning message transmission function
• RAN Information Management (RIM) function
• Configuration Transfer function

Protocol specification

3GPP TS 36.413 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP)