A twisted-pair or optical fiber segment connects only two nodes. Furthermore, the following are true:
A system connected to two twisted-pair fibers can send data on one pair and receive data on the other pair.
A fiber optic adapter connects to two optical fibers. Data is sent on one fiber and received on the other.
The most popular types of cable used for Ethernet clearly have the potential for full-duplex communication.
Stations that are connected to a hub form a CSMA/CD collision domain. The hub repeats bits onto every segment, and only one signal can be in transit at any given time.
However, it is perfectly feasible to send and receive at the same time when stations are connected to a switch. Some vendors realized ...