Class1 communication sends and receives data at regular intervals.
It is mainly used for I/O communication and motion control between PLC and sensor.

Class3 communication and UCMM communication are request/response type communication that sends and receives CIP commands at arbitrary timing.
It is mainly used for configuration and diagnosis.
Class3 communication establishes a CIP connection during communication.
UCMM communication does not establish a CIP connection during communication.