xApp anatomy: subscription manager, SDL, RMR messaging, REST API

The Four Pillars of an xApp

Every xApp interacts with the near-RT RIC platform through four fundamental interfaces. The subscription manager client sends E2 subscription requests and receives indication messages from E2 nodes. The SDL client reads and writes shared state, enabling the xApp to persist data across restarts and share information with other xApps. The RMR library handles message routing for both E2 indications and inter-xApp communication. Finally, a REST API server exposes endpoints for A1 policy reception, health checks, and configuration updates. These four pillars form the contract between the xApp and…