Realization Modified Ethernet

Solutions with strict constraints for real-time traffic need to change the hardware. In this realization, the real-time traffic bypasses upper layers and goes straight to the physical layer.

As it is possible to see, the physical layer employs a modified version of Ethernet.

Encapsulation

This realization takes advantage of Ethernet encapsulation.

Preferred topologies

The most preferred topology for these architectures is the daisy chain as it enables ease of of cabling and reduces the costs associated to that. The topology that for sure we try to avoid is the star which, on the opposite, implies a high cabling effort.

In order to successfully deploy a daisy chain network, or a ring which is also ok, it is necessary to have a switch on every connected device. In these topologies, in fact, every end station must also be able to act like a switch. For this reason, field devices complying to a Modified Ethernet realization already have it internally embedded.

Traffic handling

In Modified Ethernet realization all real-time devices must modify the Ethernet protocol; however devices which do not send real-time traffic can avoid it and can simply employ the normal protocol stack (TCP/IP, UDP/IP on normal Ethernet) in order to send non-real-time traffic.

Case study

A technology employed by several manufacturers implementing this realization is Profinet IO.