What is Full-Duplex Communication?

This post briefly defines Full-Duplex Communication. It also highlights differences between Full-Duplex and Half-Duplex Communication.


What is Full-Duplex Communication?

We define Full-Duplex Communication as communication occurring in both directions simultaneously.

Some Communications Literature will use the abbreviation FDX to denote Full-Duplex Communication.

A couple of examples of Full-Duplex Communications would be Cellular Phones and much of modern internet-based communication services (e.g., Video Communication via Skype, Face-Time, etc.).

Two women demonstrating Full-Duplex communications via cell phones.
Isolated portrait of two teenage girls with cell phones

We have the bandwidth (or a communications channel) available in these technologies in both directions.

Unlike Half-Duplex Communication, there is no means (or need) to control access to a single communications channel.

Each direction has its own communications channel and can communicate freely, at will, or whenever data is available.

An Analogy for Full-Duplex Communications

We can think of Full-Duplex Communications as being just like a two-way street on the roadways.

A Freeway is a good analogy to Full-Duplex Communications

Most modern forms of communication we use today (e.g., cell phones or tablets engaging in video conferencing, or just communicating with websites – for gaming, social media, etc.) all use Full-Duplex Communications.

In the old days, Ethernet started using Half-Duplex communications (for 10BASE-T, etc.)  However, once Ethernet moved on to faster speeds and began to use switching technology, it started supporting Full-Duplex communications.

Other forms of Communication types include:

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What is Half-Duplex Communication?

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


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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What is Simplex Communication?

This post briefly defines the term: Simplex Communication.


What is Simplex Communication?

We define simplex communication as communication that only operates in one direction.

Simplex is One Way or One Direction Communication

A couple of obvious examples of Simplex Communication would be Radio or Television Broadcasting.

Satellite Dish receives One-Way Communication (or Broadcasts) from Radio/TV Stations
Satellite dish on the modern building roof corner with blue sky in the background.

Unless you count being able to place a phone call to your Radio or TV Station, you can’t usually send traffic back to the Radio or TV Station transmitter.

ITU (International Telecommunication Union) defines Simplex Communication as a communication channel that operates in one direction at a time but maybe reversible (communication can occur in the opposite direction).

I would argue that ITU’s definition is that for Half-Duplex Communication.

Other basic terms for communications include:

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