The RIC must support E2Setup requests coming from the gNBs in Multi E2T environment. This is taken out as special item from RIC-60 (generally support new WG3 E2AP)

Description

In the WG-3 E2AP setup requests are coming from the RAN and not from the RIC.

We need to support these requests in E2M and Multiple E2T configuration. 

Requirements

• The E2T and E2M must support Setup Requests coming from the RAN
• The SCTP connection should be initiated by the RAN to the designated E2T instance. 
• In a multi-E2T configuration, the RAN knows the specific E2T instance IP address, therefore:
  • There is NO NEED to support E2T load balancing in R4. All the connections are static to the given E2T instance.
  • In case of error or failed E2T instance, THERE IS NO redirection or re-distribution of the RANs that were previously connected to other E2T instances. All of these RANs stay disconnected until the E2T with the specific IP address recovers
• It is the responsibility of the RAN to renew the connection to E2T and re-send a Setup in case of a problem.
  The E2M and E2T never send a setup to gNB RAN.
• In case of a successful setup the E2M sends the RAN E2 Setup Response with successful outcome. The E2M updates the RMR routing manager with the appropriate route and E2 instance for this RAN
• In case of a Logical problem in the RIC (for example SCTP was established, Setup Received, but can't write to RNIB) the E2M will send the RAN E2 Setup Failure message. In this case the E2M does not create a RMR route to this RAN.
• In case of SCTP problem during setup, the E2T will log the problem and do nothing (wait for the RAN to renew connection). 
• In case RAN loses its connection to E2T after it was successfully connected, the E2M:
  • Removes the RMR route to the RAN
  • Changes the status of the RAN in RNIB to disconnected
  • Write to log