There are two methods that a StudioLive CS18AI can be connected. You are either connecting it directly between a RM mixer and itself (via ethernet with AVB Switches or just directly connecting the two) or you are connecting the devices through routers to control the RM mixer functions. We explain these methods on the below PDF document from the Downloads page of the CS18AI product overview:
StudioLive CS18AI Downloads
StudioLive CS18AI + StudioLive RM Mixer Recommended Network Connection Configurations
It's important to note that regardless if you are passing audio through AVB hardware or using just a routed network, you are always controlling audio on the RM mixer. The only difference is being able to use the local I/O on the CS18AI for passing audio back and forth if you do not have AVB switches available.