Interesting reading on this topic:
Reference Guides to Half-Duplex Ethernet http://www.ethermanage.com/ethernet/quickref.html
The Quick Reference Guides to Half-Duplex Ethernet describe the configuration guidelines for the original, and now obsolete, half-duplex Ethernet system that was in wide use until the full-duplex Ethernet standard was developed in the late 1990s.
The Quick Reference Guides to Half-Duplex Ethernet contain the official half-duplex mode configuration rules for 10 and 100 Mbps Ethernet systems based on repeater hubs. Half-duplex Ethernet is another name for the original Ethernet mode of operation which uses the CSMA/CD media access protocol. Multiple segments of half-duplex Ethernet cables are linked together with repeater hubs, which serve to maintain the half-duplex signaling and timing specifications.
Also included in these Quick Reference Guides to Half-Duplex Ethernet are the configuration rules for combining segments of half-duplex Ethernet with repeater hubs. This makes it possible to verify the configuration of any half-duplex mode Ethernet system, to make sure that it meets the official timing guidelines and that it will operate correctly.
Full-duplex Ethernet is based on switching hubs and does not use the half-duplex coliision detection system. Therefore, full-duplex Ethernet links do not depend on the maintenance of round trip signal timing and other guidelines described in these Quick Reference configuration guides. Modern Ethernet systems are based on full-duplex Ethernet segments linked together with Ethernet switches, also known as switching hubs/
To repeat, the half-duplex Ethernet system described in these Quick Reference Guides is obsolete. These Quick Reference Guides to Half-Duplex Ethernet are maintained here for historical reference only.