EtherNet/IP networks rely heavily on hubs and switches. Increasingly, switches are gaining popularity while hubs hurdle toward obsolescence. The reason is pretty simple; switches give you more features for nearly the same cost.

In the past, hubs were used when cost considerations were a high priority. Unfortunately, hubs lack two features. First of all, hubs have no determinism. Hubs forward a message to all lines. This would be like a high school announcement system that displays announcements to a whole classroom. The system cannot pull little Timmy aside to tell him his mom dropped off his lunch. The whole class is distracted while that message is sent.

Switches have determinism. They can determine where a message should be sent so as not to bog other destination devices down with unnecessary messages. In other words, little Timmy gets a call from the office to find out his lunch is here and the rest of the class can listen to the teacher.

Hubs also lack full-duplex communications. They can only send or receive messages, not both at the same time. Switches can send and receive messages simultaneously. If you ever tried to yell at the principal during announcements in high school, you can appreciate this.

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