There are three main types of data communication in a computer network, categorized by the direction of signal flow between two devices: simplex, half-duplex, and full-duplex.
1. Simplex Communication
Simplex communication is a one-way communication method. The communication is unidirectional; only one of the two devices sends data, while the other only receives.
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Characteristics:
- Unidirectional data flow
- One device acts as the transmitter, the other as the receiver
- No acknowledgment or response is sent back to the transmitter
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Example:
- Radio broadcasting: A radio station transmits signals, and your radio receiver picks them up. The receiver cannot transmit back to the station.
- Television broadcasting: Similar to radio, the TV station transmits, and your TV receives.
- Keyboard to computer: While technically the computer can send signals to the keyboard (e.g., to control LEDs), the primary data flow is from the keyboard to the computer.
2. Half-Duplex Communication
Half-duplex communication allows data transmission in both directions, but only one device can transmit at a time. After one device finishes transmitting, the other can then transmit.
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Characteristics:
- Bidirectional data flow, but not simultaneously
- Devices take turns transmitting and receiving
- Requires a mechanism to indicate when a device is finished transmitting
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Example:
- Walkie-talkies: Users must press a button to talk and release it to listen. Only one person can speak at a time.
- Citizen Band (CB) radios: Similar to walkie-talkies, only one user can transmit at a time.
- Early Ethernet hubs (though mostly obsolete now): Devices connected to a hub share the same collision domain, meaning only one device can transmit at a time to avoid data collisions.
3. Full-Duplex Communication
Full-duplex communication enables simultaneous data transmission in both directions between two devices. Both devices can send and receive data at the same time, effectively doubling the bandwidth.
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Characteristics:
- Bidirectional data flow simultaneously
- Devices can transmit and receive data concurrently
- Improved efficiency and throughput compared to half-duplex
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Example:
- Modern Ethernet switches: Unlike hubs, switches create dedicated point-to-point connections between devices, allowing for full-duplex communication.
- Telephone conversations: Both parties can speak and listen at the same time.
- Modern Network Cards (NICs): They can send and receive data at the same time.
| Communication Type | Direction of Data Flow | Simultaneous Transmission | Example |
|---|---|---|---|
| Simplex | One-way | No | Radio broadcasting |
| Half-Duplex | Two-way | No | Walkie-talkie |
| Full-Duplex | Two-way | Yes | Telephone conversation, Ethernet switch |
