Late Collision is a type of collision found in the CSMA/CD protocol standard. If a collision error occurs after the first 512 bit times of data are transmitted by the transmitting station, a late collision is said to have occurred. Importantly, late collisions are not re-sent by the NIC unlike collisions occurring before the first 64 octets; it is left for the upper layers of the protocol stack to determine that there was loss of data.
Usually, possible causes are full-duplex/half-duplex mismatch, exceeded Ethernet cable length limits, incorrect cabling or a non-compliant number of hubs in the network. Bad network interface cards (NICs) can also cause late collisions, etc.
{A collision is considered late if the jam occurs after 512bit-times, or 64 bytes. Collisions that occur after the first 64bytes of a frame may be indicative of a network design problem (the network is so large the jam cannot traverse the entire length in 32bit-times), or a hardware or Ethernet firmware issue.When collisions do not propagate the network quickly enough, a collision could occur between two stations without the stations aware that the packets collided. In this situation, the frames are simply lost, and the upper-layer protocols must begin a
retransmission process to retransmit the information. These retransmissions can cause large delays, especially at the application layer.}
For example
Recently,associates have noticed extremely slow network Performance,intermittent connectivity,and connectivity,and connection losses.After entering the "show interfaces"command,you notice that the Ethernet interface is configured as 100 Mbps full-duplex and that there is evidence of late collisions.What could be the cause of this problem?
A Duplex mismatch
B A routing loop
C Trunking mode mismatch
D Improperly configured root bridge
The answer is A
