A switch is simply a bridge with many ports. When only one node is connected to a switch port, the collision domain on the shared media contains only two nodes. The two nodes in this small segment, or collision domain, consist of the switch port and the host connected to it. These small physical segments are called microsegments. Another capability emerges when only two nodes are connected. In a network that uses twisted-pair cabling, one pair is used to carry the transmitted signal from one node to the other node. A separate pair is used for the return or received signal. It is possible for signals to pass through both pairs simultaneously. The capability of communication in both directions at once is known as full duplex. Most switches are capable of supporting full duplex, as are most network interface cards (NICs). In full duplex mode, there is no contention for the media. Thus, a collision domain no longer exists. Theoretically, the bandwidth is doubled when using full duplex.

In addition to faster microprocessors and memory, two other technological advances made switches possible. Content-addressable memory (CAM) is memory that essentially works backwards compared to conventional memory. Entering data into the memory will return the associated address. Using CAM allows a switch to directly find the port that is associated with a MAC address without using search algorithms. An application-specific integrated circuit (ASIC) is a device consisting of undedicated logic gates that can be programmed to perform functions at logic speeds. Operations that might have been done in software can now be done in hardware using an ASIC. The use of these technologies greatly reduced the delays caused by software processing and enabled a switch to keep pace with the data demands of many microsegments and high bit rates.

Web Links Switch Operation http://msridhar.freeshell.org/switching.htm