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?
- prisoner26535Lv 79 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?
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?
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.
- 匿名使用者7 年前
- 阿昌Lv 79 年前