Final answer:
The network segment where only one device can communicate at a time is called a half-duplex system, similar to the operation of walkie-talkies, as opposed to full-duplex, simplex, or multiplex systems.
Step-by-step explanation:
The network segment where only one device can communicate at a time is known as a half-duplex system. In a half-duplex network, each communication channel is alternately used for transmitting and receiving signals, but not simultaneously. For example, a traditional walkie-talkie operates on a half-duplex system where one person talks while the other listens, and they must take turns speaking.
Contrasting this is the full-duplex system where communication can occur in both directions at the same time, such as in a telephone conversation. Simplex communication is one-directional, meaning signals only travel in one direction from sender to receiver with no return path (like a television broadcast), and multiplex refers to the ability to send multiple signals over a single communication channel using various techniques, not the limitation on device communication.