Duplex modes: which communication mode supports two-way traffic, but only one direction can transmit at a time (i.e., turn-taking rather than simultaneous transmission)?

Introduction / Context:
Duplex terminology describes whether endpoints can send and receive simultaneously. Choosing the correct mode is essential when designing serial links, radios, and shared media systems. The question asks for the mode that permits bidirectional communication, but not at the same instant—transmissions must alternate direction.

Given Data / Assumptions:

• Two endpoints need two-way communication.
• Only one direction can be active at any instant.
• We are naming the mode, not a specific protocol.

Concept / Approach:
Half-duplex allows both endpoints to transmit and receive, but not simultaneously. Classic examples include push-to-talk radios and older Ethernet hubs during collision recovery. Simplex allows one-way only (e.g., broadcast TV). Full-duplex allows simultaneous two-way transmission (e.g., modern switched Ethernet). “Three-quarters duplex” is not standard terminology.

Step-by-Step Solution:

Verification / Alternative check:
RS-485 multidrop and many radio systems demonstrate half-duplex behavior: devices take turns transmitting while all others listen.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing hardware capability with configured link behavior; some links can operate either half- or full-duplex.

Final Answer:
Half-duplex.