Overview
Full duplex and half duplex describe how a communication link handles data flowing in both directions. A full duplex link sends and receives at the same time over independent paths, while a half duplex link shares a single channel and must alternate between sending and receiving. The distinction determines whether devices collide, how much of the link’s bandwidth is usable, and how much delay is added when a device switches from listening to talking.
Comparison Diagram
Comparison Table
| Aspect | Full Duplex | Half Duplex |
|---|---|---|
| Data flow direction | Both directions simultaneously | One direction at a time, alternating |
| Physical channel requirement | Separate transmit and receive paths (or divided by frequency/time) | Single shared channel used by all parties |
| Collision handling | No collisions possible; each direction has its own path | Collisions possible if two devices transmit at once; needs arbitration (e.g. CSMA/CD) |
| Turnaround delay | None; a device can send and receive without waiting | Present; a device must wait for the channel to free up before switching |
| Effective throughput | Up to full bandwidth in each direction concurrently | Bandwidth shared across time, so effective throughput drops under contention |
| Hardware/protocol complexity | Requires dedicated transceivers or duplexing scheme (FDD/TDD) | Simpler transceiver; relies on a media-access protocol to coordinate turns |
| Common examples | Switched Ethernet (twisted pair), telephone calls, fiber links | Walkie-talkies, old hub-based Ethernet, CB radio, shared Wi-Fi channel |
Key Differences
- Full duplex relies on separate paths for send and receive, while half duplex forces both directions onto one shared medium
- Half duplex needs a media-access protocol like CSMA/CD to prevent two devices transmitting at once
- Switching directions in half duplex introduces turnaround delay that full duplex never has
- Full duplex effectively doubles usable capacity per link compared to a half duplex link of the same rated speed
When to Use Each
Full Duplex
- Modern switched Ethernet: Point-to-point switch links use full duplex so both ends can send and receive at line rate with zero collisions.
- Voice and video calls: Real-time two-way conversation needs simultaneous talk and listen, which full duplex provides natively.
- High-throughput server links: Data center and storage links use full duplex to maximize aggregate throughput on each connection.
Half Duplex
- Legacy shared-medium LANs: Old hub-based Ethernet or coax segments only have one physical channel, so devices must take turns transmitting.
- Two-way radio communication: Walkie-talkies and CB radios use a single RF channel, requiring users to press-to-talk and release to listen.
- Contended wireless spectrum: Wi-Fi devices on the same channel behave half duplex at the medium level since only one can transmit without collision at a time.