Ethernet

Ethernet is the standard technology used to connect nodes on wired networks. All network technologies need protocols, which are sets of rules or conventions used to send and receive data between nodes. Ethernet uses the Transmission Control Protocol/Internet Protocol (TCP/IP), and together they are used by most networks, including the Internet.

The Ethernet protocol defines a standard approach that all connected devices must use when sending and receiving data. Devices divide a stream of data into shorter pieces called frames. Each frame contains the source, destination addresses, and error-checking data so that damaged frames can be detected, discarded, and lost frames can be retransmitted. The addresses uniquely identify nodes, so no two Ethernet devices on the same network can have the same address.

With multiple (in the case of the Internet, millions) devices attempting to communicate with each other over a shared wire, there needs to be a way to ensure data is not lost or garbled during transmission. The Ethernet protocol implements a protocol known as CSMA/CD (Carrier Sense Multiple Access with Collision Detection).

The term Multiple Access refers to the fact that when one network node transmits, all the nodes on the network receive the transmission. Carrier Sense refers to the fact that before a node begins to transfer, it listens to the medium to determine whether another node is in communication. If the medium is quiet (no other nodes are transmitting), the node recognizes that this is an appropriate time to transfer.

CSMA works well to regulate communication between nodes. But an additional rule is required to handle some scenarios. Multiple nodes wanting to transmit may do so simultaneously after detecting a silence on the medium. If that happens, then a collision will occur, and data could be lost or corrupted.

Ethernet nodes also listen on the medium while in transition to ensure that they are the only node transmitting at that time. If the nodes hear their transmission returning in a garbled form, as would happen when some other node had begun to communicate its message at the same time, then they know that a collision occurred. When nodes detect a collision, they stop transmitting and wait a random amount of time or attempt to continue with the detection of silence on the medium.

Full-duplex is a data communications term that refers to the ability of devices on a network to send and receive data simultaneously. The other option is half-duplex, which means that a node can either send or receive data at a point in time. Ethernet networks are full-duplex, whereas wireless networks are half-duplex.