Switches work on the second layer of the OSI reference model, the data link layer. The CPU inside the switch will form a MAC table by matching the MAC address with the port when each port is successfully connected. In the future communication, the data packet sent to this MAC address will only be sent to its corresponding port, not all ports. Therefore, the switch can be used to divide data link layer broadcasts, that is, collision domains; but it cannot divide network layer broadcasts, that is, broadcast domains.
The switch has a very high bandwidth back bus and internal switch matrix. All the ports of the switch are connected to this back bus. After the control circuit receives the data packet, the processing port will search the address comparison table in the memory to determine the NIC (network card) of the destination MAC (the hardware address of the network card). On which port, the data packet is quickly transmitted to the destination port through the internal switching matrix. If the destination MAC does not exist, it is broadcast to all ports. After receiving the port response, the switch will “learn” a new MAC address and add it to the internal in the MAC address table. The network can also be “segmented” using a switch, which allows only necessary network traffic to pass through the switch by comparing it to a table of IP addresses. Through the filtering and forwarding of the switch, the collision domain can be effectively reduced.

AS-J890-002 MODICON Intfc Dual Ch Processor