<P> As a correctly set up CSMA / CD network link should not have late collisions, the usual possible causes are full - duplex / half - duplex mismatch, exceeded Ethernet cable length limits, or defective hardware such as incorrect cabling, non-compliant number of hubs in the network, or a bad NIC . </P> <P> The channel capture effect is a phenomenon where one user of a shared medium "captures" the medium for a significant time . During this period (usually 16 frames), other users are denied use of the medium . This effect was first seen in networks using CSMA / CD on Ethernet . Because of this effect, the most data - intense connection dominates the multiple - access wireless channel . This happens in Ethernet links because of the way nodes "back off" from the link and attempt to re-access it . In the Ethernet protocol, when a communication collision happens (when two users of the medium try to send at the same time), each user waits for a random period of time before re-accessing the link . However, a user will wait ("back off") for a random amount of time proportional to the number of times it has successively tried to access the link . The channel capture effect happens when one user continues to "win" the link . </P> <P> For example, user A and user B both try to access a quiet link at the same time . Since they detect a collision, user A waits for a random time between 0 and 1 time units and so does user B. Let's say user A chooses a lower back - off time . User A then begins to use the link and B allows it to finish sending its frame . If user A still has more to send, then user A and user B will cause another data collision . A will once again choose a random back - off time between 0 and 1, but user B will choose a back - off time between 0 and 3--because this is his second time colliding in a row . Chances are A will "win" this one again . If this continues, A will most likely win all the collision battles, and after 16 collisions (the number of tries before a user backs down for an extended period of time), user A will have "captured" the channel . </P> <P> The ability of one node to capture the entire medium is decreased as the number of nodes increases . This is because as the number of nodes increases, there is a higher probability that one of the "other" nodes will have a lower back - off time than the capturing node . </P>

What does csma/cd do how does it work