How it works
EtherNet/IP runs on standard Ethernet hardware and uses both TCP/IP and UDP/IP for data transfer. Due to the Producer/Consumer functionality supported by the CIP protocol, EtherNet/IP has various communication mechanisms at its disposal, e.g. cyclic polling, time or event triggers, multicast or simple point-to-point connections. The CIP application protocol differentiates between “implicit” I/O messages and “explicit” query/reply telegrams for configuration and data acquisition. While explicit messages are embedded into TCP frames, real-time application data is sent via UDP owing to the latter protocol’s more compact format and smaller overhead. A VLAN flag in the header of the Ethernet frame is used to prioritize time-critical data. Forming the center of a star topology network, switches prevent collisions of data from devices that are hooked up via point-to-point connections. EtherNet/IP typically achieves soft real-time performance with cycle times around 10 milliseconds. The CIPSync and CIPMotion protocol extension, an enhancement that is currently not yet available, and precise node synchronization via distributed clocks as specified in the IEEE 1588 standard are to deliver cycle times and jitter small enough to enable servo motor control.