What is Ethernet ?


Ethernet works on a principle called "Carrier Sense Multiple Access / Collision Detect" or "CSMA/CD". "Multiple Access" refers to the way multiple computers access a single Ethernet segment. Originally, this meant a single coax segment. Now this refers to all stations on the same "side" of a network switch or bridge. "Carrier Sense" means that each station on an Ethernet segment can determine if any other station is transmitting. This way, if one station is transmitting, another won't begin. However, if two stations begin transmitting at roughly the same time, carrier sense will not prevent the two transmissions from interfering with each other. This is known as a collision. The "Collision Detect" feature of Ethernet will allow a station that is transmitting to detect when another station is also transmitting (and a collision has occurred), and it will then send a jamming signal to all stations on the Ethernet segment. When this signal is received, each station will cease transmission, and will begin a randomized countdown to determine when it can transmit again.