6 S1 interface protocol structure

36.4103GPPEvolved Universal Terrestrial Radio Access Network (E-UTRAN)Release 17S1 general aspects and principlesTS

The protocol structure is following the structure defined in 3GPP TS 36.401 [2].

6.1 General

The radio network signalling over S1consists of the S1 Application Part (S1AP). The S1AP protocol consists of mechanisms to handle all procedures between the EPC and E-UTRAN. It is also capable of conveying messages transparently between the EPC and the UE without interpretation or processing by the E-UTRAN.

Over the S1 interface the S1AP protocol is, e.g., used to:

– Facilitate a set of general E-UTRAN procedures from the EPC such as paging-notification as defined by the notification Service Access Point (SAP).

– Separate each User Equipment (UE) on the protocol level for mobile specific signalling management as defined by the dedicated SAP.

– Transfer of transparent non-access signalling as defined in the dedicated SAP.

– Request of various types of E-RABs through the dedicated SAP.

– Perform the mobility function.

The E-RABs are provided by the Access Stratum (AS).

6.2 S1-MME

Figure 6.2-1 shows the protocol structure for S1-MME, following the structure described in 3GPP TS 36.401 [2].

Figure 6.2-1: Interface protocol structure for S1-MME

The Transport Network Layer (TNL) is based on IP transport, comprising the Stream Control Transmission Protocol (SCTP) on top of IP.

6.3 S1-U

Figure 6.3-1 shows the protocol structure for S1-U, following the structure described in 3GPP TS 36.401 [2].

Figure 6.3-1: Interface protocol structure for S1-U