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.).

In all of these technologies, we have bandwidth (or a communications channel) available in both directions.

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

Each direction has their 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.

Most modern forms of communication that 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 out using Half-Duplex communications (for 10BASE-T, etc.)  However, once Ethernet moved on to faster speeds and started to use switching technology, then it started supporting Full-Duplex communications as well.

Other forms of Communication types include:

• Simplex Communication and
• 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.

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

In both of these 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 sort of 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 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 does support communication in the other direction as well.

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).

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:

• Simplex Communication and
• Full-Duplex Communication

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What is Simplex Communication?

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

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

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

ITU (International Telecommunication Union) does define Simplex Communication as a communication channel that operates in one direction at a time, but that may be 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 includes:

• Half-Duplex Communication, and
• Full-Duplex Communication

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