eProsima Fast DDS

Middleware is a software layer that mediates between applications, services, sensors, drivers, and execution layers. In robotics, middleware is typically responsible for inter-process communication, message passing, hardware abstraction, and module integration within a single system. The most widely used robotics middleware is ROS (Robot Operating System), which provides a publish-subscribe message bus, service calls, and a rich ecosystem of packages.

A Transport Layer is the software layer responsible for data transmission between elements of a robotic or software system — such as processes, nodes, devices, and services. It handles serialisation, routing, reliability, and latency guarantees for messages. In robotics examples include DDS (Data Distribution Service) used by ROS 2, LCM (Lightweight Communications and Marshalling), ZeroMQ, and proprietary message buses on embedded platforms.

An API Library is a software package that exposes programmatic interfaces for communicating with a device, service, or system. In robotics it typically forms a lightweight integration layer built on top of the manufacturer's official API or an open-source project, abstracting low-level protocol details and providing language-native bindings (Python, C++, Java, etc.).

A Runtime is the environment or execution layer used to run code, load libraries, manage dependencies, and operate applications or services — either in real time or during normal system operation. In robotics this includes real-time operating system (RTOS) runtimes, ROS 2 executor runtimes, containerised execution environments (Docker, podman), and embedded C++ runtimes on microcontrollers.