Latency Analysis of Push–Pull and Publish–Subscribe Communication Protocols in U-Space Systems

In the U-Space environment, seamless communication between key stakeholders—such as U-Space Service Providers (USSP), Common Information Service Providers (CISP), and drone operators—is very important for the safe and efficient management of Unmanned Aerial Vehicle (UAV) operations. A major challenge in this context is minimizing communication latency, which directly affects the performance of time-sensitive services. This study investigates latency issues by evaluating two communication protocols: push–pull (using REST-API and ZeroMQ) and publish–subscribe (using AMQP and MQTT). Through a case study focused on drone detection, the research examines latency across critical operational activities, including conformance monitoring, flight plan confirmation, and the transmission of alerts via the USSP system under varying message intervals and payload sizes. The results indicate that while message interval has a significant influence on latency, message size has a minimal effect. Furthermore, the push–pull protocols consistently deliver lower and more stable latency compared to publish–subscribe protocols under the tested conditions. Both approaches, however, achieve latency levels that align with EASA’s operational requirements for U-Space systems.