Insights into the performance and configuration of TCP in Automotive Ethernet Networks

TCP has become an integral part of the Autosar communication stack located immediately below the Socket Adaptor layer. There are numerous use-cases for TCP in automotive networks. First TCP can be leveraged on by many higher-level protocols be it for diagnostic (DoIp), calibration protocols (XCP), service-oriented communications (SomeIP), FTP and HTTP transfer, or more specialized tasks like protocols for the control of electric vehicle charging. In addition, communication through standard TCP sockets simplifies the development and re-use of applications requiring reliable transmissions within the vehicle or with external end-systems (car2x, cloud-based services).If previous works focused on throughput as performance criterion, we here also consider the communication latencies and memory usage in the end-systems and switches. The first question explored by simulation is to quantify the importance of TCP configuration choices in the latencies that can be achieved with TCP. In particular, it is shown that turning off Nagle's algorithm in transmission and delayed acknowledgment in reception as Autosar is very beneficial in terms of latencies but at the expense of throughput. We then extend the experiments to integrate the interactions between the Socket Adaptor and TCP layers. Finally, we study the performance of TCP streams as part of a complete automotive TSN case-study made up of control traffic, audio/video streams and best-effort traffic to evaluate the impact of higher priority traffic classes on TCP streams throughput and delays. The contribution of this work is twofold. First, we draw up a panorama of the TCP features and configuration options available in Autosar. Second, through experiments on models increasingly close to an implementation, we provide quantified insights in what we can expect from TCP in terms of latencies and throughput with the different configuration options available to us.