Conformance Testing of F1AP Protocol in 5G O-RAN

The rapid development of fifth-generation (5G) communication networks is driven not only by the standardization efforts of the 3rd Generation Partnership Project (3GPP), but also by the modular, interoperable design introduced by the Open Radio Access Network (O-RAN) architecture. While O-RAN facilitates multi-vendor integration through open interfaces, it raises significant security and interoperability concerns, particularly when third-party components, such as the O-RAN Central Unit (O-CU), do not fully comply with protocol specifications. To address this challenge, we propose a conformance testing mechanism integrated into the O-RAN Distributed Unit (O-DU) that analyzes packet content and verifies the signaling behavior of newly introduced O-CUs before deployment. By proactively inspecting the F1 Application Protocol (F1AP) messages exchanged between the O-CU and O-DU, the mechanism prevents non-compliant signaling sequences and malformed messages from impacting live network operations. We implement this testing framework on a 5G standalone (SA) platform using OpenAirInterface (OAI). We simulate various abnormal F1AP scenarios, including incorrect message sequences and unauthorized field modifications in RRC and NAS payloads. Experimental results demonstrate that the proposed mechanism can detect such anomalies with high effectiveness and incurs only minimal latency overhead, offering a practical pre-deployment safeguard to enhance the security and reliability of O-RAN systems.