E2 interface and E2 Service Model

E2AP — The Real-Time Control Protocol

The E2 interface connects the near-RT RIC to E2 nodes — O-CU-CP, O-CU-UP, and O-DU — for real-time monitoring and control. The E2 Application Protocol (E2AP) runs over SCTP for reliable delivery. Key procedures include E2 Setup to establish the connection, RIC Subscription for xApps to request data streams, RIC Indication to deliver subscribed data, RIC Control to send commands to E2 nodes, and E2 Reset for error recovery. The protocol supports four interaction modes: REPORT for metric subscription, INSERT for intercepting messages, CONTROL for triggering actions, and POLICY for setting rules.