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The 1-persistent CSMA protocol

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• 1-persistent CSMA:

  • The 1-persistent CSMA protocol:

    If channel is busy, then keep sensing until the channel becomes idle As soon as the channel becomes idles, transmit the message in the next slot (I call the 1-persistent method: the stalker :))

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  • Flow chart:

    Explanation:

    If the node senses that the carrier is idle: the node transmits the message in the next slot After transmitting the message, the CSMA protocol terminates ! (Don't wait for ACK !) Graphically: If the node senses that the carrier is busy, then: The node wait until the current transmission ends then transmits the message in the next slot Graphically:

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  • Rationele of the 1-persistent CSMA:

    1-persistent CSMA is an "optimistic" protocol "I senses the channel is busy, and I believe that the system is lightly loaded I.e.: I think that I'm the only one out there that is waiting to transmit.... Graphically: So there will not be a collision after the current transmission is done:

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  • Note:

    If there are 2 or more nodes waiting for the current transmission to end, the 1-persistent CSMA protocol will always result in a collision:

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• Strength and weakness of 1-persistent CSMA

  • Strength of the 1-persistent CSMA protocol:

    Performs very well in lightly loaded systems - I.e., when there are few nodes that have messages to transmit 1-persistent CSMA will not waste any slots with a random wait period:

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  • Weakness of the 1-persistent CSMA protocol:

    1-persistent CSMA will guarantee a collision when multiple nodes are waiting (I.e., the performance will be poor under heavy load)