What is Half-Duplex Communication?

This post briefly defines the term: Half-Duplex Communication.

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What is Half-Duplex Communication?

We define Half-Duplex Communication as communication occurring in both directions but in only one direction at a time.

Some Communications Literature will use the abbreviation HDX to denote Half-Duplex Communication.

Some examples of Half-Duplex Communications systems would be Speakerphones or Walkie-Talkies.

A speakerphone is an example of Half-Duplex Communication

In both examples, legible communication can only flow if only one side is talking and the other direction (or side) is silent.

Controlling the Communication

In Half-Duplex Communication systems, there must be some control (or protocol) that decides which side (or direction) gets to transmit their information or data at a given time.

In the case of speakerphones or walkie-talkies, there needs to be some agreement (or understanding) among human beings (on both ends of the connection) on who gets to speak and when.

For electronic or automatic half-duplex systems, electronic circuitry controls which side gets to communicate or use the “channel,” when and for how long.

We will typically use Half-Duplex Communication to:

  • Support bi-directional communication, and
  • Conserve bandwidth (both directions use the same channel or bandwidth).

What are the Differences between Simplex and Half-Duplex Communication?

Half-Duplex communication is similar to Simplex Communication in that communication can only occur in one direction at a time.

However, Half-Duplex communication is different from Simplex Communication in that it also supports communication in the other direction.

It just doesn’t support bi-directional communication simultaneously.  That would be Full-Duplex Communication.

Another Example?

A good analogy for Half-Duplex Communication would be with a road construction scenario.  Consider the case where there is only one lane available to two-way traffic (over a bridge – for example).

Road Construction is an example of Half-Duplex Communication

In this case, traffic controller personnel (with signs) would be deciding and controlling which direction gets to use the available lane.  In the meantime, traffic in the other direction has to wait until they get the “go ahead” from the traffic controllers.

Other forms of Communication types include:

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Author: Darrell Smith

Darrell Smith has more than 30 years of experience as an Electrical Engineer. He has about 20 years of experience as an Applications Engineer and the remainder of his time was spent in Hardware Design and Product Marketing. He will now be sharing his wealth of knowledge on this blog.

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