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Carrier Sense Multiple Access/Collision Detection.
Posted by sagitraz
www.freepatentsonline.com/7047319.html
Posted by crouse
CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is the method Ethernet uses to deal with collisions. When a host wants to transmit, it first listens to the wire to see if anyone else is transmitting at that moment. If it is clear, it can transmit; if not, it will wait for the host that is transmitting to stop. Sometimes, two hosts decide at the same instant that the wire is clear, and collide with each other. When this happens, the hosts that were involved with the collision send a special jam signal that advises everyone on that segment of the collision. Then all the hosts wait for a random period of time before they check the wire and try transmitting again. This wait time is tiny—a few millionths of a second—and is determined by the backoff algorithm. (The backoff algorithm is the mathematical equation a host runs to come up with the random number.) The theory is that if each host waits a different amount of time, the wire should be clear for all of them when they decide to transmit again. Any Ethernet segment that uses coaxial cable (10-BASE 2, 10-BASE 5) or a hub with twisted-pair cabling is a collision environment.
Posted by thomas
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