Once vehicle functions become services rather than fixed signals, they need a way to find and talk to each other. Three protocols dominate the conversation — SOME/IP, DDS and MQTT — each with a different model and a natural home in the stack.
SOME/IP (Scalable service-Oriented MiddlewarE over IP) is the AUTOSAR standard for service-oriented communication over automotive Ethernet. It offers service discovery, remote procedure calls and publish/subscribe, and integrates tightly with classic and adaptive AUTOSAR. It is the default choice for ECU-to-ECU services inside the vehicle.
DDS (Data Distribution Service) is a data-centric publish/subscribe middleware with rich quality-of-service controls — deadlines, reliability, durability — and no central broker. It shines for high-rate, low-latency flows such as sensor and perception data, and is widely used in autonomy stacks and robotics frameworks. AUTOSAR Adaptive supports it alongside SOME/IP.
MQTT is a lightweight broker-based protocol built for telemetry over unreliable links — its natural role is the vehicle-to-cloud channel, not hard real-time in-vehicle control. In practice these protocols coexist: DDS or SOME/IP for in-vehicle services by latency and safety needs, MQTT to the cloud. The gateway and middleware bridge between them, which is exactly the integration challenge the SDV platform must solve.