A Scheduling Algorithm of Periodic Messages for Hard Real-time Communications on a Switched Ethernet

Switched Ethernet has been considered as a promising network technology for real-time communications required by process control, factory automation and other real-time applications. The switched Ethernet has many features for real-time communications such as providing a large amount of bandwidth, micro-segmentation of traffic, and full-duplex links, but to provide the hard real-time communications on the switched Ethernet, the traffic on the switch needs to be regulated not to overrun the capacity of the transmission and reception links of the switch. This paper proposes a message transmission model for hard real-time communications of periodic messages on the switched Ethernet and also proposes an algorithm to schedule the messages to be transmitted within their deadlines. The proposed scheduling algorithm is a distributed one and is performed by the source and the destination nodes without the modification of the operational features of the standard Ethernet switch. When a new periodic message needs to be transmitted, it is first checked whether it can be scheduled on both the transmission and the reception links without affecting the already-scheduled messages, and a feasible schedule is made for the new message if it is schedulable. The experiment result shows that the proposed scheduling algorithm guarantees the timely delivery of periodic messages and provides a flexible message transmission scheme to hard real-time applications by allowing them to be able to add new periodic messages while transmitting the messages that are already scheduled.