What is Ethernet?

Ethernet is a packet-switched LAN technology introduced by Xerox PARC in the early 1970s. Ethernet was designed to be a shared bus technology where multiple hosts are connected to a shared communication medium. All hosts connected to an Ethernet receive every transmission, making it possible to broadcast a packet to all hosts at the same time.

Ethernet uses a distributed access control scheme called Carrier Sense Multiple Access with Collision Detect (CSMA/CD). Multiple machines can access an Ethernet at the same time. Each machine senses whether a carrier wave is present to determine whether the network is idle before it sends a packet. Only when the network is not busy sending another message can transmission start.

In the early days of LAN technology, an Ethernet speed of 10 million bits per second (10 Mbps) (10Base-T) was quite sufficient. However, with the dramatic increase in CPU speed and advances in network technology, a 10 Mbps Ethernet became an obvious bottleneck.

Fast Ethernet uses twisted-pair wiring, was later introduced with the speed of 100 Mbps (100Base-T). Dual-speed Ethernet (10/100 Ethernet) was also introduced to accommodate both 10 and 100 Mbps connections.

By late 1990, demand has increased for even higher speed Ethernet. Therefore Gigabit Ethernet was introduced. Gigabit Ethernet (1000Base-T) extended the Ethernet technology to a bit rate of 1 gigabit per second (1 Gbps).

Each computer connected to an Ethernet network is assigned a unique 48-bit address known as its Ethernet address. Ethernet manufacturers assign unique Ethernet addresses as they produce hardware interfaces. The Ethernet address, which is also called a media access (MAC) address, is fixed in a machine-readable form on the host interface hardware.

The address can specify the physical address of one network interface, the network broadcast address, or a multicast. In addition to its MAC address, an interface must recognize a broadcast address (all 1s) and the group addresses in the case of multicast. The Ethernet interface hardware is usually given the set of addresses to recognize by the operating system during boot time.

The host interface hardware, which receives a copy of every packet that passes by, will use the destination address to determine the packets that should be passed to the host. Other packets addressed to other hosts will be ignored.