Network cabinet is basically a panel or cabinet which consists network switches.
This is generally used in big plant where there are more number of controllers, operating stations and application stations, and higher level redundancy is required.
I’ve worked with Emerson DeltaV DCS where we had 25 controllers, 22 operating stations, one AMS, 2 Enginee server, 2 OPC server and one Historian Server along with double redundancy. Function of network cabinet is to maintain communication of controllers and stations so that even when one network fails another network takes over.
credits - Thummar Ankit