匿名使用者
匿名使用者 發問時間: 社會與文化語言 · 8 年前

A CSMA/CD QUESTION

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. In this protocol, if one host sending a message collides with someone, the host will wait a random number of slot-time before trying to re-send the message. The random waiting slot time is calculated by binary exponential back-off algorithm. Now, please explain how the binary exponential back-off algorithm works? Besides, if the host experiences the second collision, what would be the range of the possible number of slot-time for this host to wait before the third trial?

4 個解答

評分
  • 8 年前
    最佳解答

    Collision in multiple access medium probably is non-issue nowadays, especially most layer 2 devices are store and forward. This design makes collision impossible.

    2012-02-28 01:59:34 補充:

    Now, please explain how the binary exponential back-off algorithm works?

    Answer:

    When a colision is detected, the sending device who detects the colision shall wait for a random amount of time then restart the transmission procedure. The binary exponential back-off algorithm is to double the window size of the "possible" random wait. See also the details below.

    Besides, if the host experiences the second collision, what would be the range of the possible number of slot-time for this host to wait before the third trial?

    Answer:

    binary exponential back-off algorithm is AKA truncated binary exponential backoff. It uses time slot t and randomly choose a backoff time between 0 through 2^c-1 time slots for collision c. For example, after collision 0 (ie, no collision), the random wait time is 0 time slot. After collision 1, random backoff is between 0 and 1 slot. After collision 2, backoff is 0..3, collision 3, backoff at 0..7.

    However, if you have collisions this bad, your random access domain is probably too big. That means you need to reduce the size of your access domain.

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  • 匿名使用者
    6 年前

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  • 阿昌
    Lv 7
    8 年前

    CSMA/ CD(載波偵聽多路訪問/衝突檢測)是在以太網網絡中使用,以確保在任何一個時間只有一個網絡節點上網絡線傳輸的協議。在這個協議中,如果一台主機發送消息與他人串通,主機將試圖重新發送消息之前等待的時間槽的隨機數。計算二進制指數回退算法的隨機等待時間槽。現在,請解釋如何二進制指數回退算法的工作嗎?此外,如果主機遇到的第二次碰撞,將是這之前等待第三次試驗的主機盡可能多的時間槽範圍?

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