On a 10Base-T network, a hub connects devices, or stations, to form a network, as shown in Figure 1. When a station sends a request or reply to another station on the network, that communication, which is transmitted as an Ethernet packet, first travels through the hub. Like a multiport repeater, the hub then broadcasts the packet to each of its ports, regardless of the actual destination of the packet. Unfortunately, hubs have a shared media segment, which is essentially a single Ethernet bus on which all stations' communications must travel. If one station is sending packets across the segment, all other stations must wait until the segment is free.
Switches employ a different architecture to reduce bandwidth contention.
Unlike a hub, a switch is an intelligent device that provides logical connections between stations. The switch maintains a table that lists all the stations connected to the switch by their hardware address and the port that corresponds to each station. When a packet passes through the switch, the switch reads the packet's destination address, refers to the table to determine the appropriate station's address and corresponding port, and then forwards the packet only to that port. For example, when Station A transmits a packet addressed to SERV1, the switch reads the address on the packet, finds SERV1's address in the table, determines which port is connected to SERV1, and forwards the packet only to SERV1's port, as shown in Figure 2 . When Station A transmits a broadcast packet, the switch transmits the broadcast packet to all active ports.