Full-Duplex
Full-duplex allows simultaneous bidirectional communication – both endpoints can send and receive at the same time. Modern switched Ethernet is full-duplex, eliminating collisions entirely. A 1 Gbps full-duplex link provides 1 Gbps in each direction simultaneously (2 Gbps aggregate).
Definition
Full-duplex enables simultaneous two-way communication. Each endpoint has dedicated transmit and receive paths – there is no contention for the medium. Switched Ethernet provides full-duplex by giving each port a dedicated collision domain. A device connected to a switch port can transmit at full line rate while simultaneously receiving at full line rate. CSMA/CD is disabled in full-duplex mode because collisions are impossible with dedicated paths. TCP connections benefit from full-duplex links because ACKs flow back simultaneously with data in the forward direction – neither direction waits for the other. Telephone circuits are full-duplex (both parties speak simultaneously). Contrast with half-duplex WiFi where the radio alternates between transmit and receive. Full-duplex WiFi is an active research area but not commercially deployed as of 2026.
Examples
- –ethtool -s eth0 duplex full – force full-duplex
- –A full-duplex 10GbE link: 10 Gbps TX + 10 Gbps RX = 20 Gbps aggregate
- –Auto-negotiation settles on full-duplex when both endpoints support it
Related Protocols
Related Terms
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.
Throughput
Throughput is the actual data transfer rate achieved on a network connection, measured in bits per second. Throughput is always less than bandwidth due to protocol overhead, congestion, packet loss, and retransmissions. TCP throughput is bounded by: min(rwnd, cwnd) / RTT.