Content for  TS 38.401  Word version:  18.4.0

Either the gNB-CU-CP or gNB-CU-UP establishes the first SCTP association with the gNB-CU-UP or gNB-CU-CP respectively using a configured TNL address.

Once the TNLA (gNB-CU-UP initiated) has been established, the gNB-CU-UP initiates the E1 Setup procedure to exchange application level configuration data.

Once the TNLA (gNB-CU-CP initiated) has been established, the gNB-CU-CP initiates the E1 Setup procedure to exchange application level configuration data.

The gNB-CU-CP may add additional SCTP Endpoint(s) to be used for E1 signalling between the gNB-CU-CP and the gNB-CU-UP pair using the gNB-CU-CP Configuration Update procedure. The gNB-CU-CP Configuration Update procedure also allows the gNB-CU-CP to request the gNB-CU-UP to modify or release TNLA(s).

The gNB-CU-UP may add additional TNL association(s) to be used for E1 signalling using a gNB-CU-CP endpoint already in use for existing TNL associations between the gNB-CU-CP and the gNB-CU-UP pair. The gNB-CU-UP CONFIGURATION UPDATE message including the gNB-CU-UP ID shall be the first E1AP message sent on an additional TNLA of an already setup E1 interface instance after the TNL association has become operational. The E1AP UE TNLA binding is a binding between a E1AP UE association and a specific TNL association for a given UE. After the E1AP UE TNLA binding is created, the gNB-CU-CP can update the UE TNLA binding by sending the E1AP message for the UE to the gNB-CU-UP via a different TNLA. The gNB-CU-UP shall update the E1AP UE TNLA binding with the new TNLA. The gNB-CU-UP Configuration Update procedure also allows the gNB-CU-UP to inform the gNB-CU-CP that the indicated TNLA(s) will be removed by the gNB-CU-UP.