CARRIER SENSE MULTIPLE ACCESS (CSMA)
There is no central access management when computers transfer on Ethernet. For this solution the Ethernet employs CSMA to coordinate transmission across multiple attached devices. CSMA is a coordination function that describe how to lead turns using a shared cable.
A computer listen to the codes i.e. it senses the carrier. If the cable is idle it starts transferring and if the cable is in use then it waits. If simultaneous transmission happens, the frames interfere with each other and this phenomenon is known collision.