To allow collision detection to work properly, the time period in which collisions are detected is restricted (512 bit-times). For Ethernet, this is 51.2us (microseconds), and for Fast Ethernet, 5.12us. For Ethernet stations, collisions can be detected up to 51.2 microseconds after the beginning of the transmission, or in other words: up to the 512th bit of the frame.
When a collision is detected by a station after it has sent the 512th bit of its frame, this is counted as a late collision.
Note that the station reporting the late collision is merely indicating the problem; it is generally not the cause of the problem. Possible causes are usually incorrect cabling or a non-compliant number of hubs in the network. Bad network interface cards (NICs) can also cause late collisions.
