With Modbus/TCP, Schneider Electric has been an early promoter of solutions based on standard Ethernet components. Advantages of this strategy are numerous: continuous chip cost reduction, continuous performance increase, multiple vendor sources, etc.
Still, in order to guarantee determinism of industrial applications, an Ethernet network used to convey real time data had to be isolated from other networks. One reason was to avoid non real-time data exchanges from impacting transfer time and processing time of critical requests such as those of an I/O scanner. But nowadays, Industrial devices embed a Web Server for diagnostic and configuration, SCADA needs to access production information through web services, etc. So a solution has to be put in place to be able to have different types of flow transferred and processed simultaneously by the network and attached devices without impacting the performance of real time exchanges. Ideally, there should be no extra hardware cost.
One solution to achieve this, still based on standard technology, is the use of Quality of Service. Quality of Service (QoS) is the ability of a network element (application, switch, etc) to have some level of assurance that its traffic and service requirements can be satisfied. QoS provides improved service to certain traffic. This is done by either raising the priority of a flow or limiting the priority of another flow .