Half-Duplex
Half-duplex allows communication in both directions but only one direction at a time. Walkie-talkies are half-duplex – one party talks while the other listens. Original Ethernet hubs were half-duplex with CSMA/CD collision detection. Modern switched Ethernet is full-duplex. WiFi remains half-duplex on each channel.
Definition
Half-duplex communication permits transmission in both directions but not simultaneously. When one device transmits, the other must wait. Early shared Ethernet (10BASE-T hubs) operated in half-duplex – all devices shared the collision domain and used CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to arbitrate access. Collisions forced both parties to back off and retry. WiFi (802.11) is inherently half-duplex on each frequency channel because the radio cannot transmit and receive simultaneously on the same frequency. This means WiFi throughput is roughly half of the link rate for bidirectional traffic. CSMA/CA (Collision Avoidance) with RTS/CTS handshakes manages WiFi medium access. The half-duplex nature of WiFi is why wired Ethernet consistently outperforms WiFi for latency-sensitive applications even when WiFi link rates appear higher.
Examples
- –ethtool eth0 | grep Duplex – shows current duplex mode
- –WiFi: 802.11ax 2.4GHz channel is half-duplex (one direction at a time)
- –Duplex mismatch: one end full, other half = 50%+ packet loss and late collisions