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    CSMA/CD (Carrier Sense Multiple Access / Collision Detection) is the protocol used in Ethernet networks to ensure that only one network node is transmitting on the network wire at any one time.

    Carrier Sense means that every Ethernet device listens to the Ethernet wire before it attempts to transmit. If the Ethernet device senses that another device is transmitting, it will wait to transmit.

    Multiple Access means that more than one Ethernet device can be sensing (listening and waiting to transmit) at a time.

    Collision Detection means that when multiple Ethernet devices accidentally transmit at the same time, they are able to detect this error.

    How Collisions Occur under CSMA/CD

    Imagine a very simple Ethernet network with only two nodes.

    Each node independently decides to send an Ethernet frame to the other node.

    Both nodes listen to the Ethernet wire and sense that no carrier is present.

    Both nodes transmit simultaneously, causing a collision.

    Both nodes detect the collision and each node waits a random amount of time before transmitting again.

    Collisions are normal on an Ethernet network. A small amount of collisions are expected in the protocol design.

    If too many nodes are transmitting on an Ethernet network, the number of collisions can rise to an unacceptable level. This can reduce the amount of available bandwidth on an Ethernet network because so much bandwidth is lost in retransmission.

    Ethernet switches greatly reduce the already minor difficulties experienced with the CSMA/CD protocol.

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    19 comments
    1. Zahid

      25 January, 2012 at 4:55 pm

      Please tell me how a node listens to the medium that its free or not? or take it as ..how a node detects a carrier on the ethernet wire ? Please reply soon.

      Reply
    2. aanchal

      24 January, 2012 at 1:52 pm

      i also need more information……

      Reply
    3. prateek

      30 October, 2011 at 9:58 am

      great
      but i need more deeply information
       

      Reply
    4. Mukesh Joshi

      29 September, 2011 at 8:25 am

      The explanation was in very simple words but was very good.
      Thanks

      Reply
    5. matacha

      16 September, 2011 at 6:32 pm

      unless CSMA/CA, CSMA/CD sends signals after collision had occured. What are other differences?

      Reply
    6. saikrishnan

      6 September, 2011 at 11:43 am

      thanks…
      that was quite easy to understand ! 

      Reply
    7. kd & Ph

      2 August, 2011 at 6:25 pm

      thanks dude good explanation
       

      Reply
    8. samuel

      26 May, 2011 at 12:23 pm

      good but differentiate with cs ma/ca

      Reply
    9. Andy

      14 May, 2011 at 5:42 am

      Thanxx…a lot it was easy to understand!!!!

      Reply
    10. arindam bhattacharjee

      12 May, 2011 at 8:38 am

      Thanx a lot for sharing

      Reply
    11. amit

      10 April, 2011 at 1:51 pm

      it is very simple explain

      Reply
    12. subardhan

      1 March, 2011 at 2:05 am

      good explanation , very helpful thanks…..

      Reply
    13. Murugesh_CIT_India

      13 December, 2010 at 1:51 pm

      good but further more detail is required… for ex: how does the station listens to the channel and how does it know the channel is busy or used… and what kind of jamming error is woken

      Reply
    14. Dhaval Vithalani

      12 November, 2010 at 4:09 am

      it is really too helpfool…Thanks a lot..

      Reply
    15. Suvadip

      3 November, 2010 at 6:17 pm

      its really helpful man, thanks a lot. 😆 😆 😆

      Reply
    16. Tan Cong

      2 November, 2010 at 3:09 pm

      It’s really good. Thanks 🙂

      Reply
    17. Dang Nguyen

      28 October, 2010 at 7:10 am

      great, thanks! 😉

      Reply
    18. shakil

      2 October, 2010 at 4:45 am

      I understood it clearly. Thank u for the explanation.

      Reply
    19. jason polydor

      15 August, 2010 at 11:50 am

      Its a simple explanation, very instructive. thanks

      Reply
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