The Ethernet System

Half-Duplex and Full-Duplex Modes

Previously, before the emergence of Ethernet switches, half-duplex mode is the typical operation for Ethernet devices.

In half-duplex mode:

• Multiple computers communicate over a single Ethernet channel via the CSMA/CD MAC protocol .
• A station (ie., the networked device) first listens to the channel, and if the channel is idle, the station transmits its data (Ethernet frames).
• Only one station can send data over the Ethernet channel at any given time.
• Data transmission rate: 10 Mb/s or 100 Mb/s

Nowadays, full-duplex mode is widely adopted by Ethernet devices and is typically enabled through the Auto-Negotiation protocol.

In full-duplex mode:

• Each station connected to a switch port does not share the Ethernet channel bandwidth on that link with any other computer.
• Devices can send and receive data simultaneously.

The Four Basic Elements of Ethernet

• The Ethernet frame — A standardized set of bits

• The Media Access Control protocol (MAC) — A set of rules embedded in each Ethernet interface that allow Ethernet stations to access the Ethernet channel, in either half-duplex or full-duplex mode

• The signaling components — Standardized electronic devices that send and receive signals over an Ethernet channel

• The physical medium — The cables and other hardware used to carry the digital Ethernet signals between computers attached to the network