Late Collisions on Ethernet Interface: Causes and Solutions

Reasons for Late Collisions on Ethernet Interface


What are two reasons that cause late collisions to increment on an Ethernet interface? (Choose two.)



Click on the arrows to vote for the correct answer

A. B. C. D. E.


A late collision is defined as any collision that occurs after the first 512 bits (or 64th byte) of the frame have been transmitted. The usual possible causes are full- duplex/half-duplex mismatch, exceeded Ethernet cable length limits, or defective hardware such as incorrect cabling, non-compliant number of hubs in the network, or a bad NIC.

Late collisions should never occur in a properly designed Ethernet network. They usually occur when Ethernet cables are too long or when there are too many repeaters in the network.

Ethernet is a widely used technology in computer networking, where devices can share the same physical medium to exchange data packets. The Ethernet protocol uses Carrier Sense Multiple Access/Collision Detection (CSMA/CD) as a medium access control method to avoid collisions between packets transmitted simultaneously.

A late collision occurs when a collision is detected after a packet has been transmitted for a certain period, which is known as the collision window. Late collisions can indicate problems with the network's configuration or cabling and can lead to performance degradation and communication failures.

The reasons that cause late collisions to increment on an Ethernet interface are:

  1. When one side of the connection is configured for half-duplex: In a half-duplex configuration, devices can transmit and receive data packets on the same channel, but not simultaneously. When a device transmits a packet, it cannot receive data from other devices on the same channel. If another device tries to transmit a packet during the transmission, a collision occurs, and the transmitting device needs to retransmit the packet. However, if the transmitting device is still sending the packet when it detects the collision, a late collision occurs.

  2. When the cable length limits are exceeded: Ethernet has a maximum cable length that can be used to avoid signal degradation and collisions. The maximum cable length depends on the Ethernet type and the data rate used. If the cable length is exceeded, the signal attenuation can cause data packets to collide, leading to late collisions.

Therefore, options B and E are the correct answers. Options A, C, and D are incorrect because:

  • Option A is incorrect because CSMA/CD is used to avoid collisions, not to cause them.
  • Option C is incorrect because the waiting time before retransmitting a packet is not related to late collisions.
  • Option D is incorrect because collisions can occur at any point during a packet transmission, not just after the 32nd byte.