Data Transmission Modes

There are three modes of data transmission that corresponds to the three types
of circuits available.
Simplex, Half – Duplex and Full – Duplex.

1. Simplex: -

• Simplex communications imply a simple method of communicating.
• In simplex communications mode, there is a one-way
communication transmission.
• Television transmission is good example of simplex communications.
The main transmitter sends out a signal, but it does not expect a
reply as the receiving units cannot issue a reply back to the
transmitter.

2. Half – Duplex: -

• In half – duplex mode, both units communicate over the same
medium, but only one unit can send at a time.
• While one is in send mode, the other unit is in receiving mode. It is
like two polite people talking to each other – one talk, the other
listens, but neither one talks at the same time.
• Thus, a half – duplex line can alternately send and receive data. It
requires two wires.

3. Full – Duplex: -

• In a half – duplex system, the line must be “Turned Around” each time the
direction is reversed.
• This involves a special switching circuit and requires a small amount of
time.

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