|  | 7.5 | Effects of Layer 2 Devices on Data Flow
| 7.5.3 | Switch segmentation of a collision domain

A LAN that uses a switched Ethernet topology creates a network that performs as though it had only two nodes – the sending node and the receiving node. These two nodes share 10 Mbps bandwidth between them, which means nearly all bandwidth is available for the transmission of data. A switched Ethernet LAN allows a LAN topology to work faster and more efficiently than a standard Ethernet LAN can, because it uses bandwidth so efficiently. In a switched Ethernet implementation, the available bandwidth can reach close to 100%.

It is important to note that even though 100% of the bandwidth may be available, Ethernet networks perform best when kept under 30-40% of full capacity. This limitation is due to Ethernet’s media access method (CSMA/CD). Bandwidth usage that exceeds the recommended limitation results in increased collisions. The purpose of LAN switching is to ease bandwidth shortages and network bottlenecks, such as that occurring between a group of PCs and a remote file server. A LAN switch is a high-speed multi-port bridge that has one port for each node, or segment, of the LAN. A switch segments a LAN into micro-segments, thereby creating collision free domains from one formerly larger collision domain.

Switched Ethernet is based on standard Ethernet. Each node is directly connected to one of its ports, or to a segment that is connected to one of the switch's ports. This creates a 10 Mbps connection between each node and each segment on the switch. A computer connected directly to an Ethernet switch is its own collision domain and accesses the full 10Mbps. As a frame enters a switch it is read for the source and/or destination address. The switch then determines which switching action will take place based on what is learned from the information in the frame. If the destination address in located on another segment, the frame is then switched to its destination.