Performance Comparison of Messaging Protocols and Serialization Formats for Digital Twins in IoV

This paper compares the performance tradeoffs of popular application-layer messaging protocols and binary serialization formats in the context of vehicle-to-cloud communication for maintaining digital twins. Of particular interest are solutions that enables emerging delay-sensitive Intelligent Transport System (ITS) features, while reducing data usage in mobile networks. The evaluated protocols are Constrained Application Protocol (CoAP), Advanced Message Queuing Protocol (AMQP), and Message Queuing Telemetry Transport (MQTT), and the serialization formats studied are Protobuf and Flatbuffers. The results show that CoAP - the only User Datagram Protocol (UDP) based protocol evaluated - has the lowest latency and overhead, but is not able to guarantee reliable transfer, even when using its confirmable message feature. For our context, the best performer that guarantees reliable transfer is MQTT. For the serialization formats, Protobuf is shown to have faster serialization speed and three times smaller serialized message size than Flatbuffers. In contrast, Flatbuffers uses less memory and has shorter deserialization time, making it an interesting alternative for applications where the vehicle is the receiver of time sensitive information. Finally, insights and implications on ITS communication are discussed.