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[4] [5] Carrier-sense multiple access with collision detection CSMA/CD is used to improve CSMA performance by terminating transmission as soon as a collision is detected, thus shortening the time required before a retry can be attempted. CSMA/CD is used by Ethernet. Carrier-sense multiple access with collision avoidance
CSMA/CD was used in now-obsolete shared-medium Ethernet variants (10BASE5, 10BASE2), and in the early versions of twisted-pair Ethernet, which used repeater hubs. Modern Ethernet networks, built with switches and full-duplex connections, no longer need to use CSMA/CD, because each Ethernet segment, or collision domain, is now isolated. CSMA/CD ...
Carrier-sense multiple access with collision avoidance (CSMA/CA) in computer networking, is a network multiple access method in which carrier sensing is used, but nodes attempt to avoid collisions by beginning transmission only after the channel is sensed to be "idle". [1] [2] When they do transmit, nodes transmit their packet data in its entirety.
Source: [1] Node D is unaware of the ongoing data transfer between node A and node B. Node D has data to send to node C, which is in the transmission range of node B. D initiates the process by sending an RTS frame to node C. Node C has already deferred its transmission until the completion of the current data transfer between node A and node B (to avoid co-channel interference at node B).
It is at least twice the time it takes for an electronic pulse (OSI Layer 1 - Physical) to travel the length of the maximum theoretical distance between two nodes. In CSMA/CD networks such as Ethernet , the slot time is an upper limit on the acquisition of the medium, a limit on the length of a packet fragment generated by a collision, and the ...
The article states that in non-persistent CSMA the station "senses the medium continually until it becomes idle". This is a perfect description for 1-persistent CSMA, a very greedy type of CSMA. In non-persistent CSMA the node checks the medium at a moment T1 and if it finds it busy it checks again after a random time interval dT.
Since bit errors are very rare in wired networks, Ethernet does not provide flow control or automatic repeat request (ARQ), meaning that incorrect packets are detected but only cancelled, not retransmitted (except in case of collisions detected by the CSMA/CD MAC layer protocol). Instead, retransmissions rely on higher-layer protocols.
By connecting each device directly to a port on the switch, either each port on a switch becomes its own collision domain (in the case of half-duplex links), or the possibility of collisions is eliminated in the case of full-duplex links. For Gigabit Ethernet and faster, no hubs or repeaters exist and all devices require full-duplex links.