Transmission modes: in which channel type is data permitted to flow in only one direction (no return path for reverse transmission)?

Introduction / Context:
Communication links are classified by directionality: simplex, half-duplex, and full-duplex. Network engineers must select the appropriate mode based on application needs and physical medium constraints. Understanding these terms is foundational to data communications and networking exams.

Given Data / Assumptions:

• “Only one direction” implies no reverse channel is available for data.
• The alternatives include standard duplexing modes.
• Terminology should align with conventional definitions.

Concept / Approach:
A simplex channel carries signals in one direction only (e.g., broadcast radio to a receiver, keyboard to CPU). Half-duplex allows both directions but not simultaneously (push-to-talk radios). Full-duplex permits simultaneous two-way transmission (telephone). “Dumb channel” is not a standard technical term for directionality and serves here as a distractor.

Step-by-Step Solution:

Verification / Alternative check:
Any data communications reference defines directionality exactly in this way; examples align with the simplex/half-duplex/full-duplex taxonomy.

Why Other Options Are Wrong:
Half-duplex and full-duplex allow reverse transmission; “dumb channel” lacks formal meaning in this context; “None” is incorrect because “simplex” is correct.

Common Pitfalls:
Confusing “simplex” with “single wire” (some full-duplex can run on a single twisted pair with echo cancellation) or assuming half-duplex equals one-way (it is two-way but not concurrent).

Final Answer:
simplex channel