For example, a FIFO of a port which is currently transmitting may begin to accept a new packet after the transmission time has passed the collision window. By transmission time is meant the time measured from the start of transmission. And the collision window is the length of time during which a collision may occur, also measured from the start of transmission. The collision window is given by the IEEE 802.3 Standard as a fixed value of 512 bit times.Therefore, for a 10 megabit per second ethernet the collision window is 51.2 microseconds; and for a 100 megabit per second ethernet the collision window is 5.12 microseconds.