The Hard Real-Time Problem on Ethernet

Popular wisdom says Ethernet is non-deterministic. This characteristic leads to consider it unsuitable for Real-Time services, since its fundamental access algorithm, called CSMA/CD, could not provide sufficiently consistent latency for deterministic applications. Simplifying, Ethernet is not able to ensure an access delay within a range known "a priori". At the moment, only three solutions for that problem in the industrial field are able to capture the attention, such as EtherCAT, Ethernet Powerlink and Profinet. This article shows analytically the Ethernet non-deterministic aspect and proposes a new solution that allows using Ethernet in industrial real time environments. Moreover it compares previous solutions with the proposed new one, pointing out pros and cons