# RTPS **slug:** `rtps` · **URL:** `/knowledge/glossary/rtps/` · **category:** Robotics Security · **reviewer:** Tatiana ### Definition RTPS (Real-Time Publish-Subscribe Protocol) is the wire-level protocol that implements the DDS communication model. Standardized by the OMG as DDS-RTPS, it defines how DDS endpoints discover each other, exchange topic data, and signal liveness — typically over UDP multicast and unicast. ### What it means RTPS is the layer below DDS that engineers and security testers most often touch directly. RTPS uses UDP multicast for participant discovery (the SPDP — Simple Participant Discovery Protocol) and unicast for endpoint discovery and data exchange. The discovery mechanism is by default open: any RTPS-capable node joining the multicast group is announced to all other participants, and topic metadata is exchanged without authentication unless DDS Security ([SROS2](/knowledge/glossary/sros2/) in ROS 2 contexts) is enabled. For offensive-security assessment in robotics deployments, RTPS testing covers: participant-discovery sniffing to enumerate the running system, topic enumeration to discover available data and control surfaces, replay and injection on multicast topics, and identification of misconfigured DDS Security policies. ### Related terms - [DDS](/knowledge/glossary/dds/) - [SROS2](/knowledge/glossary/sros2/) - [ROS2](/knowledge/glossary/ros2/) ### Authoritative sources - [DDS-RTPS specification (OMG)](https://www.omg.org/spec/DDSI-RTPS/) - [OMG DDS specifications hub](https://www.omg.org/spec/DDS/) ---