What is the difference between EtherNet/IP and EtherCAT?

One of the main differences you can notice in the way these two protocols function is that the Ethernet/IP runs the commands through a network switch, which allows integration of many devices but with possible bandwidth constraints, while the EtherCAT eliminates the need for a network switch and creates a closed-loop system that delivers the commands in a circle to each of the devices.

EtherCAT is a highly flexible network based on Ethernet technology that functions by the "processing on the fly" principle. The messages are passed on to the incoming nodes in the topology before being processed, where every node can read or extract only the relevant information they need, thus providing blazing speed and efficiency. That means that EtherCAT offers topology flexibility and synchronization, including safety protocols and multiple device profiles.

The tricky thing with EtherCAT is that data processing is enabled by special ASIC hardware on each EtherCAT slave, requiring the need for more specific hardware.

On the other side, EtherNet/IP uses the standard Ethernet layers but with the Common Industrial Protocol (CIP) over TCP/IP. This means that it uses the same hardware as the standard Ethernet networks, making it available, inexpensive, and familiar to the operators. CIP has a well-defined data representation, messaging protocol, and connection management that enables real-time industrial automation applications.

Finally, what is the best choice depends on your specific application considerations and your industrial layout. If you need higher data flow then the EtherCAT will be the better choice, whereas on the other side if you need lower speeds and less complexity, EtherNet/IP is the way to go.