Industrial Communication Guide

ETHERNET IN INDUSTRIAL USE

4. ETHERNET IN INDUSTRIAL USE 4.1.1. FUNCTION OF ETHERNET

Operating principle Unlike the master-slave method used in fielbuses, all Ethernet com- ponents are equal. This is why collisions can occur in the network when messages are exchanged. A “listening mechanism” in each device detects whether another device is sending a message and waits accordingly. If two devices happen to transmit simultane- ously, however, the transmitting components detect the collision and stop the transmission process. After a random waiting period spent “listening” to see if the line is free, each component tries to send its message again. According to the IEEE standard, Ethernet communication is random and therefore not deterministic. This has an impact on its use in industry.

Comparison of Ethernet and fieldbuses The following properties are unique to Ethernet versus fieldbuses: • Point-to-point connections only, so no terminal resistance nec- essary • Very large address space for components (approx. 281 billion individual MAC addresses) • Very large distances possible in networks since each compo- nent (such as switches and routers) refreshes the signal • High transmission speeds allow fast transmission of large data volumes (e.g. 10 Gbit/s as compared to 12 Mbit/s)

Collision of messages with standard Ethernet

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