The CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. Each stations in half-duplex Ethernet network follows the access rules by CSMA/CD. If two or more stations in a collision domain begins transmitting at the same time, collisions occur, rendering frames as garbage. To prevent future collisions, each station must be capable of detecting the occurrence of collision and must wait (idle) for a random length of time (determined by a Back-off algorithm) before retransmitting the frame. Full-duplex transmission allows simultaneous two-way transmission over point-to-point links without collision but in this case, we are being asked about Half-duplex. ÐHalf-duplex transmission has no need to reschedule frame retransmission because of CSMA/CD access methodÓ contradicts the explanation about CSMA/CD. (http://docwiki.cisco.com/wiki/EthernetTechnologies#Half-DuplexTransmission-TheCSMA.2FCDAccess_Method)