  With the growing need for automation and the ongoing merge of OT and IT,
industrial networks have to transport a high amount of heterogeneous data with
mixed criticality such as control traffic, sensor data, and configuration
messages. Current advances in IT technologies furthermore enable a new set of
automation scenarios under the roof of Industry 4.0 and IIoT where industrial
networks now have to meet new requirements in flexibility and reliability. The
necessary real-time guarantees will place significant demands on the networks.
In this paper, we identify IIoT use cases and infer real-time requirements
along several axes before bridging the gap between real-time network
technologies and the identified scenarios. We review real-time networking
technologies and present peer-reviewed works from the past 5 years for
industrial environments. We investigate how these can be applied to
controllers, systems, and embedded devices. Finally, we discuss open challenges
for real-time communication technologies to enable the identified scenarios.
The review shows academic interest in the field of real-time communication
technologies but also highlights a lack of a fixed set of standards important
for trust in safety and reliability, especially where wireless technologies are
concerned.
