Ethernet is a carrier sense multiple access with collision detection (CSMA/CD) network. Each station on the network listens for a carrier and attempts to transmit data when it senses the absence of that signal. Unfortunately, two stations may attempt to simultaneously transmit data, resulting in the occurrence of a collision. Even when one station thinks there is no carrier, it is quite possible that a carrier signal is propagating down the transmission path. Thus, a station transmitting data when its sampling of the line indicates the absence of a carrier may also result in a collision.
Because of the random nature of collisions, Ethernet bus performance is not deterministic and performance characteristics and message transmission delays are not predictable. However, over a period of time you can determine average and peak utilization, data elements which you may use to split one Ethernet LAN into two or more LANs via the use of bridges to increase individual network performance. In this appendix we will focus our attention upon determining the rate at which various length frames can flow on an Ethernet network. This information can be used by network managers and LAN administrators in conjunction with network monitoring tools to determine if a network should be segmented via the use of one or more bridges, upgraded to a higher operating rate network, or if LAN switches should be used to enhance network performance.